diff --git a/Cabal-syntax/Cabal-syntax.cabal b/Cabal-syntax/Cabal-syntax.cabal
index dd3137786e2..1d651252b45 100644
--- a/Cabal-syntax/Cabal-syntax.cabal
+++ b/Cabal-syntax/Cabal-syntax.cabal
@@ -107,6 +107,7 @@ library
     Distribution.Parsec.FieldLineStream
     Distribution.Parsec.Position
     Distribution.Parsec.Warning
+    Distribution.Parsec.Source
     Distribution.Pretty
     Distribution.SPDX
     Distribution.SPDX.License
diff --git a/Cabal-syntax/src/Distribution/FieldGrammar.hs b/Cabal-syntax/src/Distribution/FieldGrammar.hs
index e41dd6350c2..78739a37cfa 100644
--- a/Cabal-syntax/src/Distribution/FieldGrammar.hs
+++ b/Cabal-syntax/src/Distribution/FieldGrammar.hs
@@ -15,6 +15,7 @@ module Distribution.FieldGrammar
   , ParsecFieldGrammar
   , ParsecFieldGrammar'
   , parseFieldGrammar
+  , parseFieldGrammarCheckingStanzas
   , fieldGrammarKnownFieldList
   , PrettyFieldGrammar
   , PrettyFieldGrammar'
@@ -65,6 +66,20 @@ x ^^^ f = f x
 data PS ann = PS (Fields ann) [Section ann] [[Section ann]]
 
 -- | Partition field list into field map and groups of sections.
+-- Groups sections between fields. This means that the following snippet contains
+-- two section groups:
+--
+-- @
+-- -- first group
+-- some-section
+--     field: value
+-- another-section
+--     field: value
+-- foo: bar
+-- -- second group
+-- yet-another-section
+--     field: value
+-- @
 partitionFields :: [Field ann] -> (Fields ann, [[Section ann]])
 partitionFields = finalize . foldl' f (PS mempty mempty mempty)
   where
diff --git a/Cabal-syntax/src/Distribution/FieldGrammar/Parsec.hs b/Cabal-syntax/src/Distribution/FieldGrammar/Parsec.hs
index 4721aa4ad08..461a76cdd44 100644
--- a/Cabal-syntax/src/Distribution/FieldGrammar/Parsec.hs
+++ b/Cabal-syntax/src/Distribution/FieldGrammar/Parsec.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE DeriveFunctor #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 
 -- | This module provides a 'FieldGrammarParser', one way to parse
@@ -54,6 +55,7 @@
 module Distribution.FieldGrammar.Parsec
   ( ParsecFieldGrammar
   , parseFieldGrammar
+  , parseFieldGrammarCheckingStanzas
   , fieldGrammarKnownFieldList
 
     -- * Auxiliary
@@ -112,24 +114,35 @@ data Section ann = MkSection !(Name ann) [SectionArg ann] [Field ann]
 data ParsecFieldGrammar s a = ParsecFG
   { fieldGrammarKnownFields :: !(Set FieldName)
   , fieldGrammarKnownPrefixes :: !(Set FieldName)
-  , fieldGrammarParser :: !(CabalSpecVersion -> Fields Position -> ParseResult a)
+  , fieldGrammarParser :: forall src. (CabalSpecVersion -> Fields Position -> ParseResult src a)
   }
   deriving (Functor)
 
-parseFieldGrammar :: CabalSpecVersion -> Fields Position -> ParsecFieldGrammar s a -> ParseResult a
+parseFieldGrammar :: CabalSpecVersion -> Fields Position -> ParsecFieldGrammar s a -> ParseResult src a
 parseFieldGrammar v fields grammar = do
-  for_ (Map.toList (Map.filterWithKey isUnknownField fields)) $ \(name, nfields) ->
+  for_ (Map.toList (Map.filterWithKey (isUnknownField grammar) fields)) $ \(name, nfields) ->
     for_ nfields $ \(MkNamelessField pos _) ->
       parseWarning pos PWTUnknownField $ "Unknown field: " ++ show name
   -- TODO: fields allowed in this section
 
   -- parse
   fieldGrammarParser grammar v fields
-  where
-    isUnknownField k _ =
-      not $
-        k `Set.member` fieldGrammarKnownFields grammar
-          || any (`BS.isPrefixOf` k) (fieldGrammarKnownPrefixes grammar)
+
+isUnknownField :: ParsecFieldGrammar s a -> FieldName -> [NamelessField Position] -> Bool
+isUnknownField grammar k _ =
+  not $
+    k `Set.member` fieldGrammarKnownFields grammar
+      || any (`BS.isPrefixOf` k) (fieldGrammarKnownPrefixes grammar)
+
+-- | Parse a ParsecFieldGrammar and check for fields that should be stanzas.
+parseFieldGrammarCheckingStanzas :: CabalSpecVersion -> Fields Position -> ParsecFieldGrammar s a -> Set BS.ByteString -> ParseResult src a
+parseFieldGrammarCheckingStanzas v fields grammar sections = do
+  for_ (Map.toList (Map.filterWithKey (isUnknownField grammar) fields)) $ \(name, nfields) ->
+    for_ nfields $ \(MkNamelessField pos _) ->
+      if name `Set.member` sections
+        then parseFailure pos $ "'" ++ fromUTF8BS name ++ "' is a stanza, not a field. Remove the trailing ':' to parse a stanza."
+        else parseWarning pos PWTUnknownField $ "Unknown field: " ++ show name
+  fieldGrammarParser grammar v fields
 
 fieldGrammarKnownFieldList :: ParsecFieldGrammar s a -> [FieldName]
 fieldGrammarKnownFieldList = Set.toList . fieldGrammarKnownFields
@@ -145,7 +158,7 @@ instance Applicative (ParsecFieldGrammar s) where
       (\v fields -> f'' v fields <*> x'' v fields)
   {-# INLINE (<*>) #-}
 
-warnMultipleSingularFields :: FieldName -> [NamelessField Position] -> ParseResult ()
+warnMultipleSingularFields :: FieldName -> [NamelessField Position] -> ParseResult src ()
 warnMultipleSingularFields _ [] = pure ()
 warnMultipleSingularFields fn (x : xs) = do
   let pos = namelessFieldAnn x
@@ -349,7 +362,7 @@ instance FieldGrammar Parsec ParsecFieldGrammar where
 -- Parsec
 -------------------------------------------------------------------------------
 
-runFieldParser' :: [Position] -> ParsecParser a -> CabalSpecVersion -> FieldLineStream -> ParseResult a
+runFieldParser' :: [Position] -> ParsecParser a -> CabalSpecVersion -> FieldLineStream -> ParseResult src a
 runFieldParser' inputPoss p v str = case P.runParser p' [] "<field>" str of
   Right (pok, ws) -> do
     traverse_ (\(PWarning t pos w) -> parseWarning (mapPosition pos) t w) ws
@@ -378,7 +391,7 @@ runFieldParser' inputPoss p v str = case P.runParser p' [] "<field>" str of
         go n (Position row col : _) | n <= 0 = Position row (col + pcol - 1)
         go n (_ : ps) = go (n - 1) ps
 
-runFieldParser :: Position -> ParsecParser a -> CabalSpecVersion -> [FieldLine Position] -> ParseResult a
+runFieldParser :: Position -> ParsecParser a -> CabalSpecVersion -> [FieldLine Position] -> ParseResult src a
 runFieldParser pp p v ls = runFieldParser' poss p v (fieldLinesToStream ls)
   where
     poss = map (\(FieldLine pos _) -> pos) ls ++ [pp] -- add "default" position
diff --git a/Cabal-syntax/src/Distribution/Fields.hs b/Cabal-syntax/src/Distribution/Fields.hs
index 4688bf547d9..9aabb9ff7fe 100644
--- a/Cabal-syntax/src/Distribution/Fields.hs
+++ b/Cabal-syntax/src/Distribution/Fields.hs
@@ -25,11 +25,16 @@ module Distribution.Fields
     -- ** Warnings
   , PWarnType (..)
   , PWarning (..)
+  , PWarningWithSource (..)
+  , PSource (..)
   , showPWarning
+  , showPWarningWithSource
 
     -- ** Errors
   , PError (..)
+  , PErrorWithSource (..)
   , showPError
+  , showPErrorWithSource
 
     -- * Pretty printing
   , CommentPosition (..)
diff --git a/Cabal-syntax/src/Distribution/Fields/ConfVar.hs b/Cabal-syntax/src/Distribution/Fields/ConfVar.hs
index 760e2335143..e5878db3df7 100644
--- a/Cabal-syntax/src/Distribution/Fields/ConfVar.hs
+++ b/Cabal-syntax/src/Distribution/Fields/ConfVar.hs
@@ -4,11 +4,12 @@ module Distribution.Fields.ConfVar (parseConditionConfVar, parseConditionConfVar
 
 import Distribution.Compat.CharParsing (char, integral)
 import Distribution.Compat.Prelude
-import Distribution.Fields.Field (Field (..), SectionArg (..))
+import Distribution.Fields.Field (Field (..), SectionArg (..), sectionArgAnn)
 import Distribution.Fields.ParseResult
 import Distribution.Fields.Parser (readFields)
-import Distribution.Parsec (Parsec (..), Position (..), runParsecParser)
+import Distribution.Parsec (Parsec (..), runParsecParser)
 import Distribution.Parsec.FieldLineStream (fieldLineStreamFromBS)
+import Distribution.Parsec.Position
 import Distribution.Types.Condition
 import Distribution.Types.ConfVar (ConfVar (..))
 import Distribution.Version
@@ -40,10 +41,10 @@ parseConditionConfVarFromClause x =
 
 -- | Parse @'Condition' 'ConfVar'@ from section arguments provided by parsec
 -- based outline parser.
-parseConditionConfVar :: [SectionArg Position] -> ParseResult (Condition ConfVar)
-parseConditionConfVar args =
+parseConditionConfVar :: Position -> [SectionArg Position] -> ParseResult src (Condition ConfVar)
+parseConditionConfVar start_pos args =
   -- The name of the input file is irrelevant, as we reformat the error message.
-  case P.runParser (parser <* P.eof) () "<condition>" args of
+  case P.runParser (P.setPosition startPos >> parser <* P.eof) () "<condition>" args of
     Right x -> pure x
     Left err -> do
       -- Mangle the position to the actual one
@@ -59,7 +60,10 @@ parseConditionConfVar args =
               (P.errorMessages err)
       parseFailure epos msg
       pure $ Lit True
+  where
+    startPos = P.newPos "<condition>" (positionRow start_pos) (positionCol start_pos)
 
+-- | Parser for 'Condition' 'ConfVar'
 type Parser = P.Parsec [SectionArg Position] ()
 
 sepByNonEmpty :: Parser a -> Parser sep -> Parser (NonEmpty a)
@@ -132,6 +136,7 @@ parser = condOr
         | s == "false" -> Just False
       _ -> Nothing
 
+    string :: B8.ByteString -> Parser ()
     string s = tokenPrim $ \t -> case t of
       SecArgName _ s' | s == s' -> Just ()
       _ -> Nothing
@@ -142,9 +147,12 @@ parser = condOr
 
     parens = P.between (oper "(") (oper ")")
 
+    tokenPrim :: (SectionArg Position -> Maybe a) -> Parser a
     tokenPrim = P.tokenPrim prettySectionArg updatePosition
-    -- TODO: check where the errors are reported
-    updatePosition x _ _ = x
+    updatePosition :: P.SourcePos -> SectionArg Position -> [SectionArg Position] -> P.SourcePos
+    updatePosition x s _ =
+      let Position line col = sectionArgAnn s
+       in P.setSourceLine (P.setSourceColumn x col) (line)
     prettySectionArg = show
 
     fromParsec :: Parsec a => Parser a
diff --git a/Cabal-syntax/src/Distribution/Fields/ParseResult.hs b/Cabal-syntax/src/Distribution/Fields/ParseResult.hs
index 912ea7fb02f..6c2dbe5e552 100644
--- a/Cabal-syntax/src/Distribution/Fields/ParseResult.hs
+++ b/Cabal-syntax/src/Distribution/Fields/ParseResult.hs
@@ -6,6 +6,8 @@
 module Distribution.Fields.ParseResult
   ( ParseResult
   , runParseResult
+  , PSource (..)
+  , CabalFileSource (..)
   , recoverWith
   , parseWarning
   , parseWarnings
@@ -15,131 +17,160 @@ module Distribution.Fields.ParseResult
   , getCabalSpecVersion
   , setCabalSpecVersion
   , withoutWarnings
+  , liftParseResult
+  , withSource
   ) where
 
 import Distribution.Compat.Prelude
-import Distribution.Parsec.Error (PError (..))
+import Distribution.Parsec.Error (PError (..), PErrorWithSource (..))
 import Distribution.Parsec.Position (Position (..), zeroPos)
-import Distribution.Parsec.Warning (PWarnType (..), PWarning (..))
+import Distribution.Parsec.Source
+import Distribution.Parsec.Warning
 import Distribution.Version (Version)
 
 -- | A monad with failure and accumulating errors and warnings.
-newtype ParseResult a = PR
+newtype ParseResult src a = PR
   { unPR
       :: forall r
-       . PRState
-      -> (PRState -> r) -- failure, but we were able to recover a new-style spec-version declaration
-      -> (PRState -> a -> r) -- success
+       . PRState src
+      -> PRContext src
+      -> (PRState src -> r) -- failure, but we were able to recover a new-style spec-version declaration
+      -> (PRState src -> a -> r) -- success
       -> r
   }
 
+data PRContext src = PRContext
+  { prContextSource :: PSource src
+  -- ^ The file we are parsing, if known. This field is parametric because we
+  -- use the same parser for cabal files and project files.
+  }
+
 -- Note: we have version here, as we could get any version.
-data PRState = PRState ![PWarning] ![PError] !(Maybe Version)
+data PRState src = PRState ![PWarningWithSource src] ![PErrorWithSource src] !(Maybe Version)
 
-emptyPRState :: PRState
+emptyPRState :: PRState src
 emptyPRState = PRState [] [] Nothing
 
 -- | Forget 'ParseResult's warnings.
 --
 -- @since 3.4.0.0
-withoutWarnings :: ParseResult a -> ParseResult a
-withoutWarnings m = PR $ \s failure success ->
-  unPR m s failure $ \ !s1 -> success (s1 `withWarningsOf` s)
+withoutWarnings :: ParseResult src a -> ParseResult src a
+withoutWarnings m = PR $ \s ctx failure success ->
+  unPR m s ctx failure $ \ !s1 -> success (s1 `withWarningsOf` s)
   where
     withWarningsOf (PRState _ e v) (PRState w _ _) = PRState w e v
 
 -- | Destruct a 'ParseResult' into the emitted warnings and either
 -- a successful value or
 -- list of errors and possibly recovered a spec-version declaration.
-runParseResult :: ParseResult a -> ([PWarning], Either (Maybe Version, NonEmpty PError) a)
-runParseResult pr = unPR pr emptyPRState failure success
+runParseResult :: ParseResult src a -> ([PWarningWithSource src], Either (Maybe Version, NonEmpty (PErrorWithSource src)) a)
+runParseResult pr = unPR pr emptyPRState initialCtx failure success
   where
-    failure (PRState warns [] v) = (warns, Left (v, PError zeroPos "panic" :| []))
+    initialCtx = PRContext PUnknownSource
+
+    failure (PRState warns [] v) = (warns, Left (v, PErrorWithSource PUnknownSource (PError zeroPos "panic") :| []))
     failure (PRState warns (err : errs) v) = (warns, Left (v, err :| errs))
 
     success (PRState warns [] _) x = (warns, Right x)
     -- If there are any errors, don't return the result
     success (PRState warns (err : errs) v) _ = (warns, Left (v, err :| errs))
 
-instance Functor ParseResult where
-  fmap f (PR pr) = PR $ \ !s failure success ->
-    pr s failure $ \ !s' a ->
+-- | Chain parsing operations that involve 'IO' actions.
+liftParseResult :: (a -> IO (ParseResult src b)) -> ParseResult src a -> IO (ParseResult src b)
+liftParseResult f pr = unPR pr emptyPRState initialCtx failure success
+  where
+    initialCtx = PRContext PUnknownSource
+
+    failure s = return $ PR $ \s' _ctx failure' _ -> failure' (concatPRState s s')
+    success s a = do
+      pr' <- f a
+      return $ PR $ \s' ctx failure' success' -> unPR pr' (concatPRState s s') ctx failure' success'
+    concatPRState (PRState warnings errors version) (PRState warnings' errors' version') =
+      (PRState (warnings ++ warnings') (toList errors ++ errors') (version <|> version'))
+
+withSource :: src -> ParseResult src a -> ParseResult src a
+withSource source (PR pr) = PR $ \s ctx failure success ->
+  pr s (ctx{prContextSource = PKnownSource source}) failure success
+
+instance Functor (ParseResult src) where
+  fmap f (PR pr) = PR $ \ !s fp failure success ->
+    pr s fp failure $ \ !s' a ->
       success s' (f a)
   {-# INLINE fmap #-}
 
-instance Applicative ParseResult where
-  pure x = PR $ \ !s _ success -> success s x
+instance Applicative (ParseResult src) where
+  pure x = PR $ \ !s _ _ success -> success s x
   {-# INLINE pure #-}
 
-  f <*> x = PR $ \ !s0 failure success ->
-    unPR f s0 failure $ \ !s1 f' ->
-      unPR x s1 failure $ \ !s2 x' ->
+  f <*> x = PR $ \ !s0 fp failure success ->
+    unPR f s0 fp failure $ \ !s1 f' ->
+      unPR x s1 fp failure $ \ !s2 x' ->
         success s2 (f' x')
   {-# INLINE (<*>) #-}
 
-  x *> y = PR $ \ !s0 failure success ->
-    unPR x s0 failure $ \ !s1 _ ->
-      unPR y s1 failure success
+  x *> y = PR $ \ !s0 fp failure success ->
+    unPR x s0 fp failure $ \ !s1 _ ->
+      unPR y s1 fp failure success
   {-# INLINE (*>) #-}
 
-  x <* y = PR $ \ !s0 failure success ->
-    unPR x s0 failure $ \ !s1 x' ->
-      unPR y s1 failure $ \ !s2 _ ->
+  x <* y = PR $ \ !s0 fp failure success ->
+    unPR x s0 fp failure $ \ !s1 x' ->
+      unPR y s1 fp failure $ \ !s2 _ ->
         success s2 x'
   {-# INLINE (<*) #-}
 
-instance Monad ParseResult where
+instance Monad (ParseResult src) where
   return = pure
   (>>) = (*>)
 
-  m >>= k = PR $ \ !s failure success ->
-    unPR m s failure $ \ !s' a ->
-      unPR (k a) s' failure success
+  m >>= k = PR $ \ !s fp failure success ->
+    unPR m s fp failure $ \ !s' a ->
+      unPR (k a) s' fp failure success
   {-# INLINE (>>=) #-}
 
 -- | "Recover" the parse result, so we can proceed parsing.
 -- 'runParseResult' will still result in 'Nothing', if there are recorded errors.
-recoverWith :: ParseResult a -> a -> ParseResult a
-recoverWith (PR pr) x = PR $ \ !s _failure success ->
-  pr s (\ !s' -> success s' x) success
+recoverWith :: ParseResult src a -> a -> ParseResult src a
+recoverWith (PR pr) x = PR $ \ !s fp _failure success ->
+  pr s fp (\ !s' -> success s' x) success
 
 -- | Set cabal spec version.
-setCabalSpecVersion :: Maybe Version -> ParseResult ()
-setCabalSpecVersion v = PR $ \(PRState warns errs _) _failure success ->
+setCabalSpecVersion :: Maybe Version -> ParseResult src ()
+setCabalSpecVersion v = PR $ \(PRState warns errs _) _fp _failure success ->
   success (PRState warns errs v) ()
 
 -- | Get cabal spec version.
-getCabalSpecVersion :: ParseResult (Maybe Version)
-getCabalSpecVersion = PR $ \s@(PRState _ _ v) _failure success ->
+getCabalSpecVersion :: ParseResult src (Maybe Version)
+getCabalSpecVersion = PR $ \s@(PRState _ _ v) _fp _failure success ->
   success s v
 
 -- | Add a warning. This doesn't fail the parsing process.
-parseWarning :: Position -> PWarnType -> String -> ParseResult ()
-parseWarning pos t msg = PR $ \(PRState warns errs v) _failure success ->
-  success (PRState (PWarning t pos msg : warns) errs v) ()
+parseWarning :: Position -> PWarnType -> String -> ParseResult src ()
+parseWarning pos t msg = PR $ \(PRState warns errs v) ctx _failure success ->
+  success (PRState (PWarningWithSource (prContextSource ctx) (PWarning t pos msg) : warns) errs v) ()
 
 -- | Add multiple warnings at once.
-parseWarnings :: [PWarning] -> ParseResult ()
-parseWarnings newWarns = PR $ \(PRState warns errs v) _failure success ->
-  success (PRState (newWarns ++ warns) errs v) ()
+parseWarnings :: [PWarning] -> ParseResult src ()
+parseWarnings newWarns = PR $ \(PRState warns errs v) ctx _failure success ->
+  success (PRState (map (PWarningWithSource (prContextSource ctx)) newWarns ++ warns) errs v) ()
 
 -- | Add an error, but not fail the parser yet.
 --
 -- For fatal failure use 'parseFatalFailure'
-parseFailure :: Position -> String -> ParseResult ()
-parseFailure pos msg = PR $ \(PRState warns errs v) _failure success ->
-  success (PRState warns (PError pos msg : errs) v) ()
+parseFailure :: Position -> String -> ParseResult src ()
+parseFailure pos msg = PR $ \(PRState warns errs v) ctx _failure success ->
+  success (PRState warns (PErrorWithSource (prContextSource ctx) (PError pos msg) : errs) v) ()
 
 -- | Add an fatal error.
-parseFatalFailure :: Position -> String -> ParseResult a
-parseFatalFailure pos msg = PR $ \(PRState warns errs v) failure _success ->
-  failure (PRState warns (PError pos msg : errs) v)
+parseFatalFailure :: Position -> String -> ParseResult src a
+parseFatalFailure pos msg = PR $ \(PRState warns errs v) ctx failure _success ->
+  failure (PRState warns (PErrorWithSource (prContextSource ctx) (PError pos msg) : errs) v)
 
 -- | A 'mzero'.
-parseFatalFailure' :: ParseResult a
+parseFatalFailure' :: ParseResult src a
 parseFatalFailure' = PR pr
   where
-    pr (PRState warns [] v) failure _success = failure (PRState warns [err] v)
-    pr s failure _success = failure s
+    pr (PRState warns [] v) _ctx failure _success = failure (PRState warns [err] v)
+    pr s _ctx failure _success = failure s
 
-    err = PError zeroPos "Unknown fatal error"
+    err = PErrorWithSource PUnknownSource (PError zeroPos "Unknown fatal error")
diff --git a/Cabal-syntax/src/Distribution/InstalledPackageInfo.hs b/Cabal-syntax/src/Distribution/InstalledPackageInfo.hs
index 2c15d678335..350b9fee757 100644
--- a/Cabal-syntax/src/Distribution/InstalledPackageInfo.hs
+++ b/Cabal-syntax/src/Distribution/InstalledPackageInfo.hs
@@ -47,9 +47,11 @@ import Distribution.Backpack
 import Distribution.CabalSpecVersion (cabalSpecLatest)
 import Distribution.FieldGrammar
 import Distribution.FieldGrammar.FieldDescrs
+import Distribution.Fields.ParseResult
 import Distribution.Fields.Pretty
 import Distribution.ModuleName
 import Distribution.Package hiding (installedUnitId)
+import Distribution.Parsec.Source
 import Distribution.Types.ComponentName
 import Distribution.Utils.Generic (toUTF8BS)
 
@@ -98,18 +100,18 @@ parseInstalledPackageInfo
 parseInstalledPackageInfo s = case P.readFields s of
   Left err -> Left (show err :| [])
   Right fs -> case partitionFields fs of
-    (fs', _) -> case P.runParseResult $ parseFieldGrammar cabalSpecLatest fs' ipiFieldGrammar of
+    (fs', _) -> case P.runParseResult $ withSource PInstalledPackageInfo $ parseFieldGrammar cabalSpecLatest fs' ipiFieldGrammar of
       (ws, Right x) -> x `deepseq` Right (ws', x)
         where
           ws' =
-            [ P.showPWarning "" w
-            | w@(P.PWarning wt _ _) <- ws
+            [ P.showPWarningWithSource (fmap renderInstalledPackageInfoSource w)
+            | w@(P.PWarningWithSource _ (P.PWarning wt _ _)) <- ws
             , -- filter out warnings about experimental features
             wt /= P.PWTExperimental
             ]
       (_, Left (_, errs)) -> Left errs'
         where
-          errs' = fmap (P.showPError "") errs
+          errs' = fmap (P.showPErrorWithSource . fmap renderInstalledPackageInfoSource) errs
 
 -- -----------------------------------------------------------------------------
 -- Pretty-printing
diff --git a/Cabal-syntax/src/Distribution/PackageDescription/FieldGrammar.hs b/Cabal-syntax/src/Distribution/PackageDescription/FieldGrammar.hs
index 0b04b446c04..24861389b8f 100644
--- a/Cabal-syntax/src/Distribution/PackageDescription/FieldGrammar.hs
+++ b/Cabal-syntax/src/Distribution/PackageDescription/FieldGrammar.hs
@@ -361,7 +361,7 @@ testSuiteFieldGrammar =
     <*> monoidalFieldAla "code-generators" (alaList' CommaFSep Token) testStanzaCodeGenerators
       ^^^ availableSince CabalSpecV3_8 []
 
-validateTestSuite :: CabalSpecVersion -> Position -> TestSuiteStanza -> ParseResult TestSuite
+validateTestSuite :: CabalSpecVersion -> Position -> TestSuiteStanza -> ParseResult src TestSuite
 validateTestSuite cabalSpecVersion pos stanza = case testSuiteType of
   Nothing -> pure basicTestSuite
   Just tt@(TestTypeUnknown _ _) ->
@@ -503,7 +503,7 @@ benchmarkFieldGrammar =
     <*> optionalField "benchmark-module" benchmarkStanzaBenchmarkModule
     <*> blurFieldGrammar benchmarkStanzaBuildInfo buildInfoFieldGrammar
 
-validateBenchmark :: CabalSpecVersion -> Position -> BenchmarkStanza -> ParseResult Benchmark
+validateBenchmark :: CabalSpecVersion -> Position -> BenchmarkStanza -> ParseResult src Benchmark
 validateBenchmark cabalSpecVersion pos stanza = case benchmarkStanzaType of
   Nothing ->
     pure
diff --git a/Cabal-syntax/src/Distribution/PackageDescription/Parsec.hs b/Cabal-syntax/src/Distribution/PackageDescription/Parsec.hs
index 92256c98be5..c7e327ddb7f 100644
--- a/Cabal-syntax/src/Distribution/PackageDescription/Parsec.hs
+++ b/Cabal-syntax/src/Distribution/PackageDescription/Parsec.hs
@@ -20,6 +20,8 @@ module Distribution.PackageDescription.Parsec
     -- ** Parsing
   , ParseResult
   , runParseResult
+  , PSource (..)
+  , withSource
 
     -- * New-style spec-version
   , scanSpecVersion
@@ -38,7 +40,7 @@ import Distribution.Compat.Lens
 import Distribution.FieldGrammar
 import Distribution.FieldGrammar.Parsec (NamelessField (..))
 import Distribution.Fields.ConfVar (parseConditionConfVar)
-import Distribution.Fields.Field (FieldName, getName)
+import Distribution.Fields.Field (FieldName, getName, sectionArgAnn)
 import Distribution.Fields.LexerMonad (LexWarning, toPWarnings)
 import Distribution.Fields.ParseResult
 import Distribution.Fields.Parser
@@ -48,7 +50,7 @@ import Distribution.PackageDescription.FieldGrammar
 import Distribution.PackageDescription.Quirks (patchQuirks)
 import Distribution.Parsec (parsec, simpleParsecBS)
 import Distribution.Parsec.FieldLineStream (fieldLineStreamFromBS)
-import Distribution.Parsec.Position (Position (..), zeroPos)
+import Distribution.Parsec.Position (Position (..), incPos, zeroPos)
 import Distribution.Parsec.Warning (PWarnType (..))
 import Distribution.Pretty (prettyShow)
 import Distribution.Utils.Generic (breakMaybe, fromUTF8BS, toUTF8BS, unfoldrM, validateUTF8)
@@ -74,7 +76,7 @@ import qualified Text.Parsec as P
 --
 -- In Cabal 1.2 the syntax for package descriptions was changed to a format
 -- with sections and possibly indented property descriptions.
-parseGenericPackageDescription :: BS.ByteString -> ParseResult GenericPackageDescription
+parseGenericPackageDescription :: BS.ByteString -> ParseResult src GenericPackageDescription
 parseGenericPackageDescription bs = do
   -- set scanned version
   setCabalSpecVersion ver
@@ -122,7 +124,7 @@ fieldlinesToBS :: [FieldLine ann] -> BS.ByteString
 fieldlinesToBS = BS.intercalate "\n" . map (\(FieldLine _ bs) -> bs)
 
 -- Monad in which sections are parsed
-type SectionParser = StateT SectionS ParseResult
+type SectionParser src = StateT SectionS (ParseResult src)
 
 -- | State of section parser
 data SectionS = SectionS
@@ -150,7 +152,7 @@ parseGenericPackageDescription'
   -> [LexWarning]
   -> Maybe Int
   -> [Field Position]
-  -> ParseResult GenericPackageDescription
+  -> ParseResult src GenericPackageDescription
 parseGenericPackageDescription' scannedVer lexWarnings utf8WarnPos fs = do
   parseWarnings (toPWarnings lexWarnings)
   for_ utf8WarnPos $ \pos ->
@@ -220,7 +222,7 @@ parseGenericPackageDescription' scannedVer lexWarnings utf8WarnPos fs = do
     newSyntaxVersion :: CabalSpecVersion
     newSyntaxVersion = CabalSpecV1_2
 
-    maybeWarnCabalVersion :: Syntax -> PackageDescription -> ParseResult ()
+    maybeWarnCabalVersion :: Syntax -> PackageDescription -> ParseResult src ()
     maybeWarnCabalVersion syntax pkg
       | syntax == NewSyntax && specVersion pkg < newSyntaxVersion =
           parseWarning zeroPos PWTNewSyntax $
@@ -238,7 +240,7 @@ parseGenericPackageDescription' scannedVer lexWarnings utf8WarnPos fs = do
 cabalFormatVersionsDesc :: String
 cabalFormatVersionsDesc = "Current cabal-version values are listed at https://cabal.readthedocs.io/en/stable/file-format-changelog.html."
 
-goSections :: CabalSpecVersion -> [Field Position] -> SectionParser ()
+goSections :: CabalSpecVersion -> [Field Position] -> SectionParser src ()
 goSections specVer = traverse_ process
   where
     process (Field (Name pos name) _) =
@@ -261,10 +263,10 @@ goSections specVer = traverse_ process
       -> Map String CondTreeBuildInfo
       -- \^ common stanzas
       -> [Field Position]
-      -> ParseResult (CondTree ConfVar [Dependency] a)
+      -> ParseResult src (CondTree ConfVar [Dependency] a)
     parseCondTree' = parseCondTreeWithCommonStanzas specVer
 
-    parseSection :: Name Position -> [SectionArg Position] -> [Field Position] -> SectionParser ()
+    parseSection :: Name Position -> [SectionArg Position] -> [Field Position] -> SectionParser src ()
     parseSection (Name pos name) args fields
       | hasCommonStanzas == NoCommonStanzas
       , name == "common" = lift $ do
@@ -413,10 +415,10 @@ goSections specVer = traverse_ process
             parseWarning pos PWTUnknownSection $
               "Ignoring section: " ++ show name
 
-parseName :: Position -> [SectionArg Position] -> SectionParser String
+parseName :: Position -> [SectionArg Position] -> SectionParser src String
 parseName pos args = fromUTF8BS <$> parseNameBS pos args
 
-parseNameBS :: Position -> [SectionArg Position] -> SectionParser BS.ByteString
+parseNameBS :: Position -> [SectionArg Position] -> SectionParser src BS.ByteString
 -- TODO: use strict parser
 parseNameBS pos args = case args of
   [SecArgName _pos secName] ->
@@ -431,7 +433,7 @@ parseNameBS pos args = case args of
     lift $ parseFailure pos $ "Invalid name " ++ show args
     pure ""
 
-parseCommonName :: Position -> [SectionArg Position] -> ParseResult String
+parseCommonName :: Position -> [SectionArg Position] -> ParseResult src String
 parseCommonName pos args = case args of
   [SecArgName _pos secName] ->
     pure $ fromUTF8BS secName
@@ -446,7 +448,7 @@ parseCommonName pos args = case args of
     pure ""
 
 -- TODO: avoid conversion to 'String'.
-parseUnqualComponentName :: Position -> [SectionArg Position] -> SectionParser UnqualComponentName
+parseUnqualComponentName :: Position -> [SectionArg Position] -> SectionParser src UnqualComponentName
 parseUnqualComponentName pos args = mkUnqualComponentName <$> parseName pos args
 
 -- | Parse a non-recursive list of fields.
@@ -455,18 +457,18 @@ parseFields
   -> [Field Position]
   -- ^ fields to be parsed
   -> ParsecFieldGrammar' a
-  -> ParseResult a
+  -> ParseResult src a
 parseFields v fields grammar = do
   let (fs0, ss) = partitionFields fields
   traverse_ (traverse_ warnInvalidSubsection) ss
   parseFieldGrammar v fs0 grammar
 
-warnInvalidSubsection :: Section Position -> ParseResult ()
+warnInvalidSubsection :: Section Position -> ParseResult src ()
 warnInvalidSubsection (MkSection (Name pos name) _ _) =
   void $ parseFailure pos $ "invalid subsection " ++ show name
 
 parseCondTree
-  :: forall a
+  :: forall src a
    . L.HasBuildInfo a
   => CabalSpecVersion
   -> HasElif
@@ -480,7 +482,7 @@ parseCondTree
   -> (a -> [Dependency])
   -- ^ condition extractor
   -> [Field Position]
-  -> ParseResult (CondTree ConfVar [Dependency] a)
+  -> ParseResult src (CondTree ConfVar [Dependency] a)
 parseCondTree v hasElif grammar commonStanzas fromBuildInfo cond = go
   where
     go fields0 = do
@@ -494,10 +496,10 @@ parseCondTree v hasElif grammar commonStanzas fromBuildInfo cond = go
       branches <- concat <$> traverse parseIfs ss
       return $ endo $ CondNode x (cond x) branches
 
-    parseIfs :: [Section Position] -> ParseResult [CondBranch ConfVar [Dependency] a]
+    parseIfs :: [Section Position] -> ParseResult src [CondBranch ConfVar [Dependency] a]
     parseIfs [] = return []
-    parseIfs (MkSection (Name _ name) test fields : sections) | name == "if" = do
-      test' <- parseConditionConfVar test
+    parseIfs (MkSection (Name pos name) test fields : sections) | name == "if" = do
+      test' <- parseConditionConfVar (startOfSection (incPos 2 pos) test) test
       fields' <- go fields
       (elseFields, sections') <- parseElseIfs sections
       return (CondBranch test' fields' elseFields : sections')
@@ -507,7 +509,7 @@ parseCondTree v hasElif grammar commonStanzas fromBuildInfo cond = go
 
     parseElseIfs
       :: [Section Position]
-      -> ParseResult (Maybe (CondTree ConfVar [Dependency] a), [CondBranch ConfVar [Dependency] a])
+      -> ParseResult src (Maybe (CondTree ConfVar [Dependency] a), [CondBranch ConfVar [Dependency] a])
     parseElseIfs [] = return (Nothing, [])
     parseElseIfs (MkSection (Name pos name) args fields : sections) | name == "else" = do
       unless (null args) $
@@ -516,10 +518,10 @@ parseCondTree v hasElif grammar commonStanzas fromBuildInfo cond = go
       elseFields <- go fields
       sections' <- parseIfs sections
       return (Just elseFields, sections')
-    parseElseIfs (MkSection (Name _ name) test fields : sections)
+    parseElseIfs (MkSection (Name pos name) test fields : sections)
       | hasElif == HasElif
       , name == "elif" = do
-          test' <- parseConditionConfVar test
+          test' <- parseConditionConfVar (startOfSection (incPos 4 pos) test) test
           fields' <- go fields
           (elseFields, sections') <- parseElseIfs sections
           -- we parse an empty 'Fields', to get empty value for a node
@@ -530,6 +532,12 @@ parseCondTree v hasElif grammar commonStanzas fromBuildInfo cond = go
       (,) Nothing <$> parseIfs sections
     parseElseIfs sections = (,) Nothing <$> parseIfs sections
 
+startOfSection :: Position -> [SectionArg Position] -> Position
+-- The case where we have no args is the start of the section
+startOfSection defaultPos [] = defaultPos
+-- Otherwise the start of the section is the position of the first argument.
+startOfSection _ (cond : _) = sectionArgAnn cond
+
 {- Note [Accumulating parser]
 
 Note: Outdated a bit
@@ -618,7 +626,7 @@ instance FromBuildInfo BenchmarkStanza where
   fromBuildInfo' _ bi = BenchmarkStanza Nothing Nothing Nothing bi
 
 parseCondTreeWithCommonStanzas
-  :: forall a
+  :: forall src a
    . L.HasBuildInfo a
   => CabalSpecVersion
   -> ParsecFieldGrammar' a
@@ -628,7 +636,7 @@ parseCondTreeWithCommonStanzas
   -> Map String CondTreeBuildInfo
   -- ^ common stanzas
   -> [Field Position]
-  -> ParseResult (CondTree ConfVar [Dependency] a)
+  -> ParseResult src (CondTree ConfVar [Dependency] a)
 parseCondTreeWithCommonStanzas v grammar fromBuildInfo commonStanzas fields = do
   (fields', endo) <- processImports v fromBuildInfo commonStanzas fields
   x <- parseCondTree v hasElif grammar commonStanzas fromBuildInfo (view L.targetBuildDepends) fields'
@@ -637,7 +645,7 @@ parseCondTreeWithCommonStanzas v grammar fromBuildInfo commonStanzas fields = do
     hasElif = specHasElif v
 
 processImports
-  :: forall a
+  :: forall src a
    . L.HasBuildInfo a
   => CabalSpecVersion
   -> (BuildInfo -> a)
@@ -645,7 +653,7 @@ processImports
   -> Map String CondTreeBuildInfo
   -- ^ common stanzas
   -> [Field Position]
-  -> ParseResult ([Field Position], CondTree ConfVar [Dependency] a -> CondTree ConfVar [Dependency] a)
+  -> ParseResult src ([Field Position], CondTree ConfVar [Dependency] a -> CondTree ConfVar [Dependency] a)
 processImports v fromBuildInfo commonStanzas = go []
   where
     hasCommonStanzas = specHasCommonStanzas v
@@ -677,7 +685,7 @@ processImports v fromBuildInfo commonStanzas = go []
       pure $ (fields', \x -> foldr (mergeCommonStanza fromBuildInfo) x acc)
 
 -- | Warn on "import" fields, also map to Maybe, so erroneous fields can be filtered
-warnImport :: CabalSpecVersion -> Field Position -> ParseResult (Maybe (Field Position))
+warnImport :: CabalSpecVersion -> Field Position -> ParseResult src (Maybe (Field Position))
 warnImport v (Field (Name pos name) _) | name == "import" = do
   if specHasCommonStanzas v == NoCommonStanzas
     then parseWarning pos PWTUnknownField "Unknown field: import. You should set cabal-version: 2.2 or larger to use common stanzas"
@@ -731,7 +739,7 @@ onAllBranches p = go mempty
 --
 -- * don't use undefined flags (very bad)
 -- * define flags which are unused (just bad)
-checkForUndefinedFlags :: GenericPackageDescription -> ParseResult ()
+checkForUndefinedFlags :: GenericPackageDescription -> ParseResult src ()
 checkForUndefinedFlags gpd = do
   let definedFlags, usedFlags :: Set.Set FlagName
       definedFlags = toSetOf (L.genPackageFlags . traverse . getting flagName) gpd
@@ -748,7 +756,7 @@ checkForUndefinedFlags gpd = do
 
 -- | Since @cabal-version: 1.24@ one can specify @custom-setup@.
 -- Let us require it.
-checkForUndefinedCustomSetup :: GenericPackageDescription -> ParseResult ()
+checkForUndefinedCustomSetup :: GenericPackageDescription -> ParseResult src ()
 checkForUndefinedCustomSetup gpd = do
   let pd = packageDescription gpd
   let csv = specVersion pd
@@ -923,7 +931,7 @@ libFieldNames = fieldGrammarKnownFieldList (libraryFieldGrammar LMainLibName)
 -- Supplementary build information
 -------------------------------------------------------------------------------
 
-parseHookedBuildInfo :: BS.ByteString -> ParseResult HookedBuildInfo
+parseHookedBuildInfo :: BS.ByteString -> ParseResult src HookedBuildInfo
 parseHookedBuildInfo bs = case readFields' bs of
   Right (fs, lexWarnings) -> do
     parseHookedBuildInfo' lexWarnings fs
@@ -933,7 +941,7 @@ parseHookedBuildInfo bs = case readFields' bs of
 parseHookedBuildInfo'
   :: [LexWarning]
   -> [Field Position]
-  -> ParseResult HookedBuildInfo
+  -> ParseResult src HookedBuildInfo
 parseHookedBuildInfo' lexWarnings fs = do
   parseWarnings (toPWarnings lexWarnings)
   (mLibFields, exes) <- stanzas fs
@@ -941,24 +949,24 @@ parseHookedBuildInfo' lexWarnings fs = do
   biExes <- traverse parseExe exes
   return (mLib, biExes)
   where
-    parseLib :: Fields Position -> ParseResult (Maybe BuildInfo)
+    parseLib :: Fields Position -> ParseResult src (Maybe BuildInfo)
     parseLib fields
       | Map.null fields = pure Nothing
       | otherwise = Just <$> parseFieldGrammar cabalSpecLatest fields buildInfoFieldGrammar
 
-    parseExe :: (UnqualComponentName, Fields Position) -> ParseResult (UnqualComponentName, BuildInfo)
+    parseExe :: (UnqualComponentName, Fields Position) -> ParseResult src (UnqualComponentName, BuildInfo)
     parseExe (n, fields) = do
       bi <- parseFieldGrammar cabalSpecLatest fields buildInfoFieldGrammar
       pure (n, bi)
 
-    stanzas :: [Field Position] -> ParseResult (Fields Position, [(UnqualComponentName, Fields Position)])
+    stanzas :: [Field Position] -> ParseResult src (Fields Position, [(UnqualComponentName, Fields Position)])
     stanzas fields = do
       let (hdr0, exes0) = breakMaybe isExecutableField fields
       hdr <- toFields hdr0
       exes <- unfoldrM (traverse toExe) exes0
       pure (hdr, exes)
 
-    toFields :: [Field Position] -> ParseResult (Fields Position)
+    toFields :: [Field Position] -> ParseResult src (Fields Position)
     toFields fields = do
       let (fields', ss) = partitionFields fields
       traverse_ (traverse_ warnInvalidSubsection) ss
@@ -966,7 +974,7 @@ parseHookedBuildInfo' lexWarnings fs = do
 
     toExe
       :: ([FieldLine Position], [Field Position])
-      -> ParseResult ((UnqualComponentName, Fields Position), Maybe ([FieldLine Position], [Field Position]))
+      -> ParseResult src ((UnqualComponentName, Fields Position), Maybe ([FieldLine Position], [Field Position]))
     toExe (fss, fields) = do
       name <- runFieldParser zeroPos parsec cabalSpecLatest fss
       let (hdr0, rest) = breakMaybe isExecutableField fields
diff --git a/Cabal-syntax/src/Distribution/Parsec.hs b/Cabal-syntax/src/Distribution/Parsec.hs
index d0197616fd6..a3f695bc95b 100644
--- a/Cabal-syntax/src/Distribution/Parsec.hs
+++ b/Cabal-syntax/src/Distribution/Parsec.hs
@@ -24,11 +24,16 @@ module Distribution.Parsec
     -- ** Warnings
   , PWarnType (..)
   , PWarning (..)
+  , PWarningWithSource (..)
+  , PSource (..)
   , showPWarning
+  , showPWarningWithSource
 
     -- ** Errors
   , PError (..)
+  , PErrorWithSource (..)
   , showPError
+  , showPErrorWithSource
 
     -- * Position
   , Position (..)
@@ -58,10 +63,12 @@ import Data.Char (digitToInt, intToDigit)
 import Data.List (transpose)
 import Distribution.CabalSpecVersion
 import Distribution.Compat.Prelude
-import Distribution.Parsec.Error (PError (..), showPError)
+import Distribution.Parsec.Error (PError (..), PErrorWithSource (..), showPError, showPErrorWithSource)
+
+import Data.Monoid (Last (..))
 import Distribution.Parsec.FieldLineStream (FieldLineStream, fieldLineStreamFromBS, fieldLineStreamFromString)
 import Distribution.Parsec.Position (Position (..), incPos, retPos, showPos, zeroPos)
-import Distribution.Parsec.Warning (PWarnType (..), PWarning (..), showPWarning)
+import Distribution.Parsec.Warning
 import Numeric (showIntAtBase)
 import Prelude ()
 
@@ -255,6 +262,12 @@ instance Parsec Bool where
           caseWarning =
             "Boolean values are case sensitive, use 'True' or 'False'."
 
+instance Parsec a => Parsec (Last a) where
+  parsec = parsecLast
+
+parsecLast :: (Parsec a, CabalParsing m) => m (Last a)
+parsecLast = (Last . Just <$> parsec) <|> pure mempty
+
 -- | @[^ ,]@
 parsecToken :: CabalParsing m => m String
 parsecToken = parsecHaskellString <|> ((P.munch1 (\x -> not (isSpace x) && x /= ',') P.<?> "identifier") >>= checkNotDoubleDash)
diff --git a/Cabal-syntax/src/Distribution/Parsec/Error.hs b/Cabal-syntax/src/Distribution/Parsec/Error.hs
index 46114c3ea98..8c1d7326b33 100644
--- a/Cabal-syntax/src/Distribution/Parsec/Error.hs
+++ b/Cabal-syntax/src/Distribution/Parsec/Error.hs
@@ -1,22 +1,34 @@
+{-# LANGUAGE DeriveFunctor #-}
 {-# LANGUAGE DeriveGeneric #-}
 
 module Distribution.Parsec.Error
   ( PError (..)
+  , PErrorWithSource (..)
   , showPError
+  , showPErrorWithSource
   ) where
 
 import Distribution.Compat.Prelude
 import Distribution.Parsec.Position
+import Distribution.Parsec.Source
+import Distribution.Parsec.Warning -- TODO: Move PSource into own module
 import System.FilePath (normalise)
 import Prelude ()
 
 -- | Parser error.
-data PError = PError Position String
+data PError = PError {perrorPosition :: Position, perrorMessage :: String}
   deriving (Show, Generic)
 
+data PErrorWithSource src = PErrorWithSource {perrorSource :: !(PSource src), perror :: !PError}
+  deriving (Show, Generic, Functor)
+
 instance Binary PError
 instance NFData PError where rnf = genericRnf
 
 showPError :: FilePath -> PError -> String
 showPError fpath (PError pos msg) =
   normalise fpath ++ ":" ++ showPos pos ++ ": " ++ msg
+
+showPErrorWithSource :: PErrorWithSource String -> String
+showPErrorWithSource (PErrorWithSource source (PError pos msg)) =
+  showPError (showPSourceAsFilePath source) (PError pos msg)
diff --git a/Cabal-syntax/src/Distribution/Parsec/Source.hs b/Cabal-syntax/src/Distribution/Parsec/Source.hs
new file mode 100644
index 00000000000..5d662679680
--- /dev/null
+++ b/Cabal-syntax/src/Distribution/Parsec/Source.hs
@@ -0,0 +1,45 @@
+{-# LANGUAGE DeriveFunctor #-}
+{-# LANGUAGE DeriveGeneric #-}
+
+module Distribution.Parsec.Source
+  ( PSource (..)
+  , CabalFileSource (..)
+  , InstalledPackageInfoSource (..)
+  , renderCabalFileSource
+  , renderInstalledPackageInfoSource
+  ) where
+
+import qualified Data.ByteString as BS
+import Distribution.Compat.Prelude
+import Prelude ()
+
+-- | The source of a parse error
+data PSource src
+  = PKnownSource src
+  | PUnknownSource
+  deriving (Ord, Show, Generic, Functor)
+
+newtype CabalFileSource
+  = PCabalFile (FilePath, BS.ByteString)
+  deriving (Ord, Show, Generic)
+
+data InstalledPackageInfoSource
+  = PInstalledPackageInfo
+  deriving (Eq, Ord, Show, Generic)
+
+renderCabalFileSource :: CabalFileSource -> String
+renderCabalFileSource (PCabalFile (path, _)) = path
+
+renderInstalledPackageInfoSource :: InstalledPackageInfoSource -> String
+renderInstalledPackageInfoSource PInstalledPackageInfo = ""
+
+instance Eq CabalFileSource where
+  PCabalFile (path, _) == PCabalFile (path', _) = path == path'
+
+instance Eq src => Eq (PSource src) where
+  PKnownSource src == PKnownSource src' = src == src'
+  PUnknownSource == PUnknownSource = True
+  _ == _ = False
+
+instance Binary src => Binary (PSource src)
+instance NFData src => NFData (PSource src) where rnf = genericRnf
diff --git a/Cabal-syntax/src/Distribution/Parsec/Warning.hs b/Cabal-syntax/src/Distribution/Parsec/Warning.hs
index ce7ffc4d6e9..65b1471b054 100644
--- a/Cabal-syntax/src/Distribution/Parsec/Warning.hs
+++ b/Cabal-syntax/src/Distribution/Parsec/Warning.hs
@@ -1,13 +1,19 @@
+{-# LANGUAGE DeriveFunctor #-}
 {-# LANGUAGE DeriveGeneric #-}
 
 module Distribution.Parsec.Warning
   ( PWarning (..)
+  , PWarningWithSource (..)
+  , PSource (..)
+  , showPSourceAsFilePath
   , PWarnType (..)
   , showPWarning
+  , showPWarningWithSource
   ) where
 
 import Distribution.Compat.Prelude
 import Distribution.Parsec.Position
+import Distribution.Parsec.Source
 import System.FilePath (normalise)
 import Prelude ()
 
@@ -67,12 +73,25 @@ instance Binary PWarnType
 instance NFData PWarnType where rnf = genericRnf
 
 -- | Parser warning.
-data PWarning = PWarning !PWarnType !Position String
+data PWarning = PWarning {pwarningType :: !PWarnType, pwarningPosition :: !Position, pwarningMessage :: !String}
   deriving (Eq, Ord, Show, Generic)
 
+data PWarningWithSource src = PWarningWithSource {pwarningSource :: !(PSource src), pwarning :: !PWarning}
+  deriving (Eq, Ord, Show, Generic, Functor)
+
 instance Binary PWarning
 instance NFData PWarning where rnf = genericRnf
 
 showPWarning :: FilePath -> PWarning -> String
 showPWarning fpath (PWarning _ pos msg) =
   normalise fpath ++ ":" ++ showPos pos ++ ": " ++ msg
+
+showPWarningWithSource :: PWarningWithSource String -> String
+showPWarningWithSource (PWarningWithSource source pwarn) =
+  showPWarning (showPSourceAsFilePath source) pwarn
+
+showPSourceAsFilePath :: PSource String -> String
+showPSourceAsFilePath source =
+  case source of
+    PKnownSource src -> src
+    PUnknownSource -> "???"
diff --git a/Cabal-tests/tests/CheckTests.hs b/Cabal-tests/tests/CheckTests.hs
index aa2f1e9b041..dfc716f6e33 100644
--- a/Cabal-tests/tests/CheckTests.hs
+++ b/Cabal-tests/tests/CheckTests.hs
@@ -6,10 +6,11 @@ import Test.Tasty
 import Test.Tasty.Golden.Advanced (goldenTest)
 
 import Data.Algorithm.Diff                    (PolyDiff (..), getGroupedDiff)
-import Distribution.Fields                    (runParseResult)
+import Distribution.Fields.ParseResult
 import Distribution.PackageDescription.Check  (checkPackage)
 import Distribution.PackageDescription.Parsec (parseGenericPackageDescription)
 import Distribution.Parsec
+import Distribution.Parsec.Source
 import Distribution.Utils.Generic             (fromUTF8BS, toUTF8BS)
 import System.Directory                       (setCurrentDirectory)
 import System.Environment                     (getArgs, withArgs)
@@ -62,16 +63,16 @@ checkTests = testGroup "regressions"
 checkTest :: FilePath -> TestTree
 checkTest fp = cabalGoldenTest fp correct $ do
     contents <- BS.readFile input
-    let res =  parseGenericPackageDescription contents
+    let res =  withSource (PCabalFile (fp, contents)) $ parseGenericPackageDescription contents
     let (ws, x) = runParseResult res
 
     return $ toUTF8BS $ case x of
         Right gpd      ->
             -- Note: parser warnings are reported by `cabal check`, but not by
             -- D.PD.Check functionality.
-            unlines (map (showPWarning fp) ws) ++
+            unlines (map (showPWarningWithSource . fmap renderCabalFileSource) ws) ++
             unlines (map show (checkPackage gpd))
-        Left (_, errs) -> unlines $ map (("ERROR: " ++) . showPError fp) $ NE.toList errs
+        Left (_, errs) -> unlines $ map (("ERROR: " ++) . showPErrorWithSource . fmap renderCabalFileSource) $ NE.toList errs
   where
     input = "tests" </> "ParserTests" </> "regressions" </> fp
     correct = replaceExtension input "check"
diff --git a/Cabal-tests/tests/HackageTests.hs b/Cabal-tests/tests/HackageTests.hs
index dbad37c30f4..1265c6cb13e 100644
--- a/Cabal-tests/tests/HackageTests.hs
+++ b/Cabal-tests/tests/HackageTests.hs
@@ -24,6 +24,8 @@ import Distribution.PackageDescription.Check       (PackageCheck (..), checkPack
 import Distribution.PackageDescription.PrettyPrint (showGenericPackageDescription)
 import Distribution.PackageDescription.Quirks      (patchQuirks)
 import Distribution.Simple.Utils                   (fromUTF8BS, toUTF8BS)
+import Distribution.Fields.ParseResult
+import Distribution.Parsec.Source
 import Numeric                                     (showFFloat)
 import System.Directory                            (getXdgDirectory, XdgDirectory(XdgCache, XdgConfig), getAppUserDataDirectory, doesDirectoryExist)
 import System.Environment                          (lookupEnv)
@@ -152,7 +154,7 @@ readFieldTest fpath bs = case Parsec.readFields bs' of
 parseParsecTest :: Bool -> FilePath -> B.ByteString -> IO ParsecResult
 parseParsecTest keepGoing fpath bs = do
     let (warnings, result) = Parsec.runParseResult $
-                             Parsec.parseGenericPackageDescription bs
+                             withSource (PCabalFile (fpath, bs)) $ Parsec.parseGenericPackageDescription bs
 
     let w | null warnings = 0
           | otherwise     = 1
@@ -163,10 +165,10 @@ parseParsecTest keepGoing fpath bs = do
             return (ParsecResult 1 w 0)
 
         Left (_, errors) | keepGoing -> do
-            traverse_ (putStrLn . Parsec.showPError fpath) errors
+            traverse_ (putStrLn . Parsec.showPErrorWithSource . fmap renderCabalFileSource) errors
             return (ParsecResult 1 w 1)
                          | otherwise -> do
-            traverse_ (putStrLn . Parsec.showPError fpath) errors
+            traverse_ (putStrLn . Parsec.showPErrorWithSource . fmap renderCabalFileSource) errors
             exitFailure
 
 -- | A hook to make queries on Hackage
@@ -197,7 +199,7 @@ instance NFData ParsecResult where
 parseCheckTest :: FilePath -> B.ByteString -> IO CheckResult
 parseCheckTest fpath bs = do
     let (warnings, parsec) = Parsec.runParseResult $
-                             Parsec.parseGenericPackageDescription bs
+                             withSource (PCabalFile (fpath, bs)) $ Parsec.parseGenericPackageDescription bs
     case parsec of
         Right gpd -> do
             let checks = checkPackage gpd
@@ -210,7 +212,7 @@ parseCheckTest fpath bs = do
             -- one for file, many checks
             return (CheckResult 1 (w warnings) 0 0 0 0 0 0 <> foldMap toCheckResult checks)
         Left (_, errors) -> do
-            traverse_ (putStrLn . Parsec.showPError fpath) errors
+            traverse_ (putStrLn . Parsec.showPErrorWithSource . fmap renderCabalFileSource) errors
             exitFailure
 
 -- checkCppFlags :: BuildInfo -> IO BuildInfo
@@ -304,7 +306,7 @@ roundtripTest testFieldsTransform fpath bs = do
 {- FOURMOLU_DISABLE -}
     parse phase c = do
         let (_, x') = Parsec.runParseResult $
-                      Parsec.parseGenericPackageDescription c
+                      withSource (PCabalFile (fpath, c)) $ Parsec.parseGenericPackageDescription c
         case x' of
             Right gpd -> pure gpd
             Left (_, errs) -> do
diff --git a/Cabal-tests/tests/NoThunks.hs b/Cabal-tests/tests/NoThunks.hs
index 6a81475dc03..a53d404dd1e 100644
--- a/Cabal-tests/tests/NoThunks.hs
+++ b/Cabal-tests/tests/NoThunks.hs
@@ -21,7 +21,8 @@ import Distribution.Compat.NonEmptySet        (NonEmptySet)
 import Distribution.Compiler                  (CompilerFlavor, PerCompilerFlavor)
 import Distribution.Fields                    (runParseResult)
 import Distribution.ModuleName                (ModuleName)
-import Distribution.PackageDescription.Parsec (parseGenericPackageDescription)
+import Distribution.PackageDescription.Parsec (parseGenericPackageDescription, withSource)
+import Distribution.Parsec.Source
 import Distribution.SPDX                      (License, LicenseExceptionId, LicenseExpression, LicenseId, LicenseRef, SimpleLicenseExpression)
 import Distribution.System                    (Arch, OS)
 import Distribution.Utils.Path                (SymbolicPathX)
@@ -45,7 +46,7 @@ main = defaultMain $ testGroup "nothunks"
 noThunksParse :: IO ()
 noThunksParse = do
     bs <- BS.readFile "Cabal/Cabal.cabal" <|> BS.readFile "../Cabal/Cabal.cabal"
-    let res = parseGenericPackageDescription bs
+    let res = withSource (PCabalFile ("Cabal.cabal", bs)) $ parseGenericPackageDescription bs
     gpd <- either (assertFailure . show) return $ snd $
         runParseResult res
 
diff --git a/Cabal-tests/tests/ParserTests.hs b/Cabal-tests/tests/ParserTests.hs
index 3990f19fc79..8368ed19451 100644
--- a/Cabal-tests/tests/ParserTests.hs
+++ b/Cabal-tests/tests/ParserTests.hs
@@ -13,16 +13,18 @@ import Test.Tasty.HUnit
 import Control.Monad                               (unless, void)
 import Data.Algorithm.Diff                         (PolyDiff (..), getGroupedDiff)
 import Data.Maybe                                  (isNothing)
-import Distribution.Fields                         (runParseResult)
+import Distribution.Fields                         (pwarning)
 import Distribution.PackageDescription             (GenericPackageDescription)
 import Distribution.PackageDescription.Parsec      (parseGenericPackageDescription)
 import Distribution.PackageDescription.PrettyPrint (showGenericPackageDescription)
-import Distribution.Parsec                         (PWarnType (..), PWarning (..), showPError, showPWarning)
+import Distribution.Parsec                         (PWarnType (..), PWarning (..), showPErrorWithSource, showPWarningWithSource)
 import Distribution.Pretty                         (prettyShow)
+import Distribution.Fields.ParseResult
 import Distribution.Utils.Generic                  (fromUTF8BS, toUTF8BS)
 import System.Directory                            (setCurrentDirectory)
 import System.Environment                          (getArgs, withArgs)
 import System.FilePath                             (replaceExtension, (</>))
+import Distribution.Parsec.Source
 
 import qualified Data.ByteString       as BS
 import qualified Data.ByteString.Char8 as BS8
@@ -79,12 +81,12 @@ warningTest :: PWarnType -> FilePath -> TestTree
 warningTest wt fp = testCase (show wt) $ do
     contents <- BS.readFile $ "tests" </> "ParserTests" </> "warnings" </> fp
 
-    let res =  parseGenericPackageDescription contents
+    let res =  withSource (PCabalFile (fp, contents)) $ parseGenericPackageDescription contents
     let (warns, x) = runParseResult res
 
     assertBool ("should parse successfully: " ++ show x) $ isRight x
 
-    case warns of
+    case map pwarning warns of
         [PWarning wt' _ _] -> assertEqual "warning type" wt wt'
         []                 -> assertFailure "got no warnings"
         _                  -> assertFailure $ "got multiple warnings: " ++ show warns
@@ -135,7 +137,7 @@ errorTests = testGroup "errors"
 errorTest :: FilePath -> TestTree
 errorTest fp = cabalGoldenTest fp correct $ do
     contents <- BS.readFile input
-    let res =  parseGenericPackageDescription contents
+    let res =  withSource (PCabalFile (fp, contents)) $ parseGenericPackageDescription contents
     let (_, x) = runParseResult res
 
     return $ toUTF8BS $ case x of
@@ -143,7 +145,7 @@ errorTest fp = cabalGoldenTest fp correct $ do
             "UNEXPECTED SUCCESS\n" ++
             showGenericPackageDescription gpd
         Left (v, errs) ->
-            unlines $ ("VERSION: " ++ show v) : map (showPError fp) (NE.toList errs)
+            unlines $ ("VERSION: " ++ show v) : map (showPErrorWithSource . fmap renderCabalFileSource) (NE.toList errs)
   where
     input = "tests" </> "ParserTests" </> "errors" </> fp
     correct = replaceExtension input "errors"
@@ -212,18 +214,18 @@ regressionTest fp = testGroup fp
 formatGoldenTest :: FilePath -> TestTree
 formatGoldenTest fp = cabalGoldenTest "format" correct $ do
     contents <- BS.readFile input
-    let res = parseGenericPackageDescription contents
+    let res = withSource (PCabalFile (fp, contents)) $ parseGenericPackageDescription contents
     let (warns, x) = runParseResult res
 
     return $ toUTF8BS $ case x of
         Right gpd ->
-            unlines (map (showPWarning fp) warns)
+            unlines (map (showPWarningWithSource . fmap renderCabalFileSource) warns)
             ++ showGenericPackageDescription gpd
         Left (csv, errs) ->
             unlines $
                 "ERROR" :
                 maybe "unknown-version" prettyShow csv :
-                map (showPError fp) (NE.toList errs)
+                map (showPErrorWithSource . fmap renderCabalFileSource) (NE.toList errs)
   where
     input = "tests" </> "ParserTests" </> "regressions" </> fp
     correct = replaceExtension input "format"
@@ -232,11 +234,11 @@ formatGoldenTest fp = cabalGoldenTest "format" correct $ do
 treeDiffGoldenTest :: FilePath -> TestTree
 treeDiffGoldenTest fp = ediffGolden goldenTest "expr" exprFile $ do
     contents <- BS.readFile input
-    let res =  parseGenericPackageDescription contents
+    let res = withSource (PCabalFile (fp, contents)) $ parseGenericPackageDescription contents
     let (_, x) = runParseResult res
     case x of
         Right gpd      -> pure (toExpr gpd)
-        Left (_, errs) -> fail $ unlines $ "ERROR" : map (showPError fp) (NE.toList errs)
+        Left (_, errs) -> fail $ unlines $ "ERROR" : map (showPErrorWithSource . fmap renderCabalFileSource) (NE.toList errs)
   where
     input = "tests" </> "ParserTests" </> "regressions" </> fp
     exprFile = replaceExtension input "expr"
@@ -269,11 +271,11 @@ formatRoundTripTest fp = testCase "roundtrip" $ do
   where
     parse :: BS.ByteString -> IO GenericPackageDescription
     parse c = do
-        let (_, x') = runParseResult $ parseGenericPackageDescription c
+        let (_, x') = runParseResult $ withSource (PCabalFile (fp, c)) $ parseGenericPackageDescription c
         case x' of
             Right gpd      -> pure gpd
             Left (_, errs) -> do
-                void $ assertFailure $ unlines (map (showPError fp) $ NE.toList errs)
+                void $ assertFailure $ unlines (map (showPErrorWithSource . fmap renderCabalFileSource) $ NE.toList errs)
                 fail "failure"
     input = "tests" </> "ParserTests" </> "regressions" </> fp
 {- FOURMOLU_ENABLE -}
diff --git a/Cabal/src/Distribution/Simple/Compiler.hs b/Cabal/src/Distribution/Simple/Compiler.hs
index 6c81b50f891..543ff1e0083 100644
--- a/Cabal/src/Distribution/Simple/Compiler.hs
+++ b/Cabal/src/Distribution/Simple/Compiler.hs
@@ -50,6 +50,7 @@ module Distribution.Simple.Compiler
   , interpretPackageDBStack
   , coercePackageDB
   , coercePackageDBStack
+  , readPackageDb
 
     -- * Support for optimisation levels
   , OptimisationLevel (..)
@@ -93,7 +94,9 @@ module Distribution.Simple.Compiler
   , showProfDetailLevel
   ) where
 
+import Distribution.Compat.CharParsing
 import Distribution.Compat.Prelude
+import Distribution.Parsec
 import Distribution.Pretty
 import Prelude ()
 
@@ -104,6 +107,7 @@ import Distribution.Version
 
 import Language.Haskell.Extension
 
+import Data.Bool (bool)
 import qualified Data.Map as Map (lookup)
 import System.Directory (canonicalizePath)
 
@@ -203,6 +207,15 @@ data PackageDBX fp
 instance Binary fp => Binary (PackageDBX fp)
 instance Structured fp => Structured (PackageDBX fp)
 
+-- | Parse a PackageDB stack entry
+--
+-- @since 3.7.0.0
+readPackageDb :: String -> Maybe PackageDB
+readPackageDb "clear" = Nothing
+readPackageDb "global" = Just GlobalPackageDB
+readPackageDb "user" = Just UserPackageDB
+readPackageDb other = Just (SpecificPackageDB (makeSymbolicPath other))
+
 -- | We typically get packages from several databases, and stack them
 -- together. This type lets us be explicit about that stacking. For example
 -- typical stacks include:
@@ -294,20 +307,36 @@ data OptimisationLevel
 instance Binary OptimisationLevel
 instance Structured OptimisationLevel
 
+instance Parsec OptimisationLevel where
+  parsec = parsecOptimisationLevel
+
+parsecOptimisationLevel :: CabalParsing m => m OptimisationLevel
+parsecOptimisationLevel = boolParser <|> intParser
+  where
+    boolParser = bool NoOptimisation NormalOptimisation <$> parsec
+    intParser = intToOptimisationLevel <$> integral
+
 flagToOptimisationLevel :: Maybe String -> OptimisationLevel
 flagToOptimisationLevel Nothing = NormalOptimisation
 flagToOptimisationLevel (Just s) = case reads s of
-  [(i, "")]
-    | i >= fromEnum (minBound :: OptimisationLevel)
-        && i <= fromEnum (maxBound :: OptimisationLevel) ->
-        toEnum i
-    | otherwise ->
-        error $
-          "Bad optimisation level: "
-            ++ show i
-            ++ ". Valid values are 0..2"
+  [(i, "")] -> intToOptimisationLevel i
   _ -> error $ "Can't parse optimisation level " ++ s
 
+intToOptimisationLevel :: Int -> OptimisationLevel
+intToOptimisationLevel i
+  | i >= minLevel && i <= maxLevel = toEnum i
+  | otherwise =
+      error $
+        "Bad optimisation level: "
+          ++ show i
+          ++ ". Valid values are "
+          ++ show minLevel
+          ++ ".."
+          ++ show maxLevel
+  where
+    minLevel = fromEnum (minBound :: OptimisationLevel)
+    maxLevel = fromEnum (maxBound :: OptimisationLevel)
+
 -- ------------------------------------------------------------
 
 -- * Debug info levels
@@ -327,6 +356,12 @@ data DebugInfoLevel
 instance Binary DebugInfoLevel
 instance Structured DebugInfoLevel
 
+instance Parsec DebugInfoLevel where
+  parsec = parsecDebugInfoLevel
+
+parsecDebugInfoLevel :: CabalParsing m => m DebugInfoLevel
+parsecDebugInfoLevel = flagToDebugInfoLevel . pure <$> parsecToken
+
 flagToDebugInfoLevel :: Maybe String -> DebugInfoLevel
 flagToDebugInfoLevel Nothing = NormalDebugInfo
 flagToDebugInfoLevel (Just s) = case reads s of
@@ -574,6 +609,12 @@ data ProfDetailLevel
 instance Binary ProfDetailLevel
 instance Structured ProfDetailLevel
 
+instance Parsec ProfDetailLevel where
+  parsec = parsecProfDetailLevel
+
+parsecProfDetailLevel :: CabalParsing m => m ProfDetailLevel
+parsecProfDetailLevel = flagToProfDetailLevel <$> parsecToken
+
 flagToProfDetailLevel :: String -> ProfDetailLevel
 flagToProfDetailLevel "" = ProfDetailDefault
 flagToProfDetailLevel s =
diff --git a/Cabal/src/Distribution/Simple/InstallDirs.hs b/Cabal/src/Distribution/Simple/InstallDirs.hs
index 41143ea36ee..818b9273bfd 100644
--- a/Cabal/src/Distribution/Simple/InstallDirs.hs
+++ b/Cabal/src/Distribution/Simple/InstallDirs.hs
@@ -2,6 +2,7 @@
 {-# LANGUAGE DeriveFunctor #-}
 {-# LANGUAGE DeriveGeneric #-}
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE RankNTypes #-}
 
 -----------------------------------------------------------------------------
@@ -44,6 +45,7 @@ module Distribution.Simple.InstallDirs
   , compilerTemplateEnv
   , packageTemplateEnv
   , abiTemplateEnv
+  , installDirsGrammar
   , installDirsTemplateEnv
   ) where
 
@@ -51,9 +53,13 @@ import Distribution.Compat.Prelude
 import Prelude ()
 
 import Distribution.Compat.Environment (lookupEnv)
+import Distribution.Compat.Lens (Lens')
 import Distribution.Compiler
+import Distribution.FieldGrammar
 import Distribution.Package
+import Distribution.Parsec
 import Distribution.Pretty
+import Distribution.Simple.Flag
 import Distribution.Simple.InstallDirs.Internal
 import Distribution.System
 
@@ -506,6 +512,12 @@ instance Read PathTemplate where
     , (template, "") <- reads path
     ]
 
+instance Parsec PathTemplate where
+  parsec = parsecPathTemplate
+
+parsecPathTemplate :: CabalParsing m => m PathTemplate
+parsecPathTemplate = toPathTemplate <$> parsecFilePath
+
 -- ---------------------------------------------------------------------------
 -- Internal utilities
 
@@ -552,3 +564,81 @@ foreign import CALLCONV unsafe "shlobj.h SHGetFolderPathW"
                               -> Prelude.IO CInt
 #endif
 {- FOURMOLU_ENABLE -}
+
+-- ---------------------------------------------------------------------------
+-- FieldGrammar
+
+installDirsGrammar :: ParsecFieldGrammar' (InstallDirs (Flag PathTemplate))
+installDirsGrammar =
+  InstallDirs
+    <$> optionalFieldDef "prefix" installDirsPrefixLens mempty
+    <*> optionalFieldDef "bindir" installDirsBindirLens mempty
+    <*> optionalFieldDef "libdir" installDirsLibdirLens mempty
+    <*> optionalFieldDef "libsubdir" installDirsLibsubdirLens mempty
+    <*> optionalFieldDef "dynlibdir" installDirsDynlibdirLens mempty
+    <*> pure NoFlag -- flibdir
+    <*> optionalFieldDef "libexecdir" installDirsLibexecdirLens mempty
+    <*> optionalFieldDef "libexecsubdir" installDirsLibexecsubdirLens mempty
+    <*> pure NoFlag -- includedir
+    <*> optionalFieldDef "datadir" installDirsDatadirLens mempty
+    <*> optionalFieldDef "datasubdir" installDirsDatasubdirLens mempty
+    <*> optionalFieldDef "docdir" installDirsDocdirLens mempty
+    <*> pure NoFlag -- mandir
+    <*> optionalFieldDef "htmldir" installDirsHtmldirLens mempty
+    <*> optionalFieldDef "haddockdir" installDirsHaddockdirLens mempty
+    <*> optionalFieldDef "sysconfdir" installDirsSysconfdirLens mempty
+
+-- ---------------------------------------------------------------------------
+-- Lenses
+
+installDirsPrefixLens :: Lens' (InstallDirs a) a
+installDirsPrefixLens f c = fmap (\x -> c{prefix = x}) (f (prefix c))
+{-# INLINEABLE installDirsPrefixLens #-}
+
+installDirsBindirLens :: Lens' (InstallDirs a) a
+installDirsBindirLens f c = fmap (\x -> c{bindir = x}) (f (bindir c))
+{-# INLINEABLE installDirsBindirLens #-}
+
+installDirsLibdirLens :: Lens' (InstallDirs a) a
+installDirsLibdirLens f c = fmap (\x -> c{libdir = x}) (f (libdir c))
+{-# INLINEABLE installDirsLibdirLens #-}
+
+installDirsLibsubdirLens :: Lens' (InstallDirs a) a
+installDirsLibsubdirLens f c = fmap (\x -> c{libsubdir = x}) (f (libsubdir c))
+{-# INLINEABLE installDirsLibsubdirLens #-}
+
+installDirsDynlibdirLens :: Lens' (InstallDirs a) a
+installDirsDynlibdirLens f c = fmap (\x -> c{dynlibdir = x}) (f (dynlibdir c))
+{-# INLINEABLE installDirsDynlibdirLens #-}
+
+installDirsLibexecdirLens :: Lens' (InstallDirs a) a
+installDirsLibexecdirLens f c = fmap (\x -> c{libexecdir = x}) (f (libexecdir c))
+{-# INLINEABLE installDirsLibexecdirLens #-}
+
+installDirsLibexecsubdirLens :: Lens' (InstallDirs a) a
+installDirsLibexecsubdirLens f c = fmap (\x -> c{libexecsubdir = x}) (f (libexecsubdir c))
+{-# INLINEABLE installDirsLibexecsubdirLens #-}
+
+installDirsDatadirLens :: Lens' (InstallDirs a) a
+installDirsDatadirLens f c = fmap (\x -> c{datadir = x}) (f (datadir c))
+{-# INLINEABLE installDirsDatadirLens #-}
+
+installDirsDatasubdirLens :: Lens' (InstallDirs a) a
+installDirsDatasubdirLens f c = fmap (\x -> c{datasubdir = x}) (f (datasubdir c))
+{-# INLINEABLE installDirsDatasubdirLens #-}
+
+installDirsDocdirLens :: Lens' (InstallDirs a) a
+installDirsDocdirLens f c = fmap (\x -> c{docdir = x}) (f (docdir c))
+{-# INLINEABLE installDirsDocdirLens #-}
+
+installDirsHtmldirLens :: Lens' (InstallDirs a) a
+installDirsHtmldirLens f c = fmap (\x -> c{htmldir = x}) (f (htmldir c))
+{-# INLINEABLE installDirsHtmldirLens #-}
+
+installDirsHaddockdirLens :: Lens' (InstallDirs a) a
+installDirsHaddockdirLens f c = fmap (\x -> c{haddockdir = x}) (f (haddockdir c))
+{-# INLINEABLE installDirsHaddockdirLens #-}
+
+installDirsSysconfdirLens :: Lens' (InstallDirs a) a
+installDirsSysconfdirLens f c = fmap (\x -> c{sysconfdir = x}) (f (sysconfdir c))
+{-# INLINEABLE installDirsSysconfdirLens #-}
diff --git a/Cabal/src/Distribution/Simple/PackageDescription.hs b/Cabal/src/Distribution/Simple/PackageDescription.hs
index d0ee9d9f86b..e0f1806d6a1 100644
--- a/Cabal/src/Distribution/Simple/PackageDescription.hs
+++ b/Cabal/src/Distribution/Simple/PackageDescription.hs
@@ -18,6 +18,8 @@ module Distribution.Simple.PackageDescription
 
     -- * Utility Parsing function
   , parseString
+  , readAndParseFile
+  , flattenDups
   ) where
 
 import Distribution.Compat.Prelude
@@ -31,11 +33,13 @@ import Distribution.PackageDescription.Parsec
   ( parseGenericPackageDescription
   , parseHookedBuildInfo
   )
-import Distribution.Parsec.Error (showPError)
+import Distribution.Parsec.Error (showPErrorWithSource)
+import Distribution.Parsec.Source
 import Distribution.Parsec.Warning
   ( PWarnType (PWTExperimental)
   , PWarning (..)
-  , showPWarning
+  , PWarningWithSource (..)
+  , showPWarningWithSource
   )
 import Distribution.Simple.Errors
 import Distribution.Simple.Utils (dieWithException, equating, warn)
@@ -70,7 +74,7 @@ readHookedBuildInfo =
 --
 -- Argument order is chosen to encourage partial application.
 readAndParseFile
-  :: (BS.ByteString -> ParseResult a)
+  :: (BS.ByteString -> ParseResult CabalFileSource a)
   -- ^ File contents to final value parser
   -> Verbosity
   -- ^ Verbosity level
@@ -90,7 +94,7 @@ readAndParseFile parser verbosity mbWorkDir fpath = do
   parseString parser verbosity upath bs
 
 parseString
-  :: (BS.ByteString -> ParseResult a)
+  :: (BS.ByteString -> ParseResult CabalFileSource a)
   -- ^ File contents to final value parser
   -> Verbosity
   -- ^ Verbosity level
@@ -99,38 +103,41 @@ parseString
   -> BS.ByteString
   -> IO a
 parseString parser verbosity name bs = do
-  let (warnings, result) = runParseResult (parser bs)
-  traverse_ (warn verbosity . showPWarning name) (flattenDups verbosity warnings)
+  let (warnings, result) = runParseResult $ withSource (PCabalFile (name, bs)) (parser bs)
+  traverse_ (warn verbosity . showPWarningWithSource . fmap renderCabalFileSource) (flattenDups verbosity warnings)
   case result of
     Right x -> return x
     Left (_, errors) -> do
-      traverse_ (warn verbosity . showPError name) errors
+      traverse_ (warn verbosity . showPErrorWithSource . fmap renderCabalFileSource) errors
       dieWithException verbosity $ FailedParsing name
 
 -- | Collapse duplicate experimental feature warnings into single warning, with
 -- a count of further sites
-flattenDups :: Verbosity -> [PWarning] -> [PWarning]
+flattenDups :: Verbosity -> [PWarningWithSource src] -> [PWarningWithSource src]
 flattenDups verbosity ws
   | verbosity <= normal = rest ++ experimentals
   | otherwise = ws -- show all instances
   where
-    (exps, rest) = partition (\(PWarning w _ _) -> w == PWTExperimental) ws
+    (exps, rest) = partition (\(PWarningWithSource _ (PWarning w _ _)) -> w == PWTExperimental) ws
     experimentals =
       concatMap flatCount
-        . groupBy (equating warningStr)
-        . sortBy (comparing warningStr)
+        . groupBy (equating (warningStr . pwarning))
+        . sortBy (comparing (warningStr . pwarning))
         $ exps
 
     warningStr (PWarning _ _ w) = w
 
     -- flatten if we have 3 or more examples
-    flatCount :: [PWarning] -> [PWarning]
+    flatCount :: [PWarningWithSource src] -> [PWarningWithSource src]
     flatCount w@[] = w
     flatCount w@[_] = w
     flatCount w@[_, _] = w
-    flatCount (PWarning t pos w : xs) =
-      [ PWarning
-          t
-          pos
-          (w <> printf " (and %d more occurrences)" (length xs))
+    flatCount (PWarningWithSource source (PWarning t pos w) : xs) =
+      [ PWarningWithSource
+          source
+          ( PWarning
+              t
+              pos
+              (w <> printf " (and %d more occurrences)" (length xs))
+          )
       ]
diff --git a/Cabal/src/Distribution/Simple/Setup/Config.hs b/Cabal/src/Distribution/Simple/Setup/Config.hs
index 729b466b4da..67945bd4d43 100644
--- a/Cabal/src/Distribution/Simple/Setup/Config.hs
+++ b/Cabal/src/Distribution/Simple/Setup/Config.hs
@@ -890,15 +890,6 @@ configureOptions showOrParseArgs =
 readPackageDbList :: String -> [Maybe PackageDB]
 readPackageDbList str = [readPackageDb str]
 
--- | Parse a PackageDB stack entry
---
--- @since 3.7.0.0
-readPackageDb :: String -> Maybe PackageDB
-readPackageDb "clear" = Nothing
-readPackageDb "global" = Just GlobalPackageDB
-readPackageDb "user" = Just UserPackageDB
-readPackageDb other = Just (SpecificPackageDB (makeSymbolicPath other))
-
 showPackageDbList :: [Maybe PackageDB] -> [String]
 showPackageDbList = map showPackageDb
 
diff --git a/Cabal/src/Distribution/Types/DumpBuildInfo.hs b/Cabal/src/Distribution/Types/DumpBuildInfo.hs
index 99020febc35..0e9cb8ce8d5 100644
--- a/Cabal/src/Distribution/Types/DumpBuildInfo.hs
+++ b/Cabal/src/Distribution/Types/DumpBuildInfo.hs
@@ -5,6 +5,7 @@ module Distribution.Types.DumpBuildInfo
   ) where
 
 import Distribution.Compat.Prelude
+import Distribution.Parsec
 
 data DumpBuildInfo
   = NoDumpBuildInfo
@@ -13,3 +14,12 @@ data DumpBuildInfo
 
 instance Binary DumpBuildInfo
 instance Structured DumpBuildInfo
+
+instance Parsec DumpBuildInfo where
+  parsec = parsecDumpBuildInfo
+
+parsecDumpBuildInfo :: CabalParsing m => m DumpBuildInfo
+parsecDumpBuildInfo = boolToDumpBuildInfo <$> parsec
+
+boolToDumpBuildInfo :: Bool -> DumpBuildInfo
+boolToDumpBuildInfo bool = if bool then DumpBuildInfo else NoDumpBuildInfo
diff --git a/cabal-install-solver/src/Distribution/Solver/Types/ProjectConfigPath.hs b/cabal-install-solver/src/Distribution/Solver/Types/ProjectConfigPath.hs
index be6ded8cff2..257ba808aaa 100644
--- a/cabal-install-solver/src/Distribution/Solver/Types/ProjectConfigPath.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Types/ProjectConfigPath.hs
@@ -9,9 +9,11 @@ module Distribution.Solver.Types.ProjectConfigPath
     , nullProjectConfigPath
     , consProjectConfigPath
     , unconsProjectConfigPath
+    , currentProjectConfigPath
 
     -- * Messages
     , docProjectConfigPath
+    , docProjectImportedBy
     , docProjectConfigFiles
     , cyclicalImportMsg
     , untrimmedUriImportMsg
@@ -131,6 +133,13 @@ docProjectConfigPath (ProjectConfigPath (p :| [])) = quoteUntrimmed p
 docProjectConfigPath (ProjectConfigPath (p :| ps)) = vcat $ quoteUntrimmed p :
     [ text " " <+> text "imported by:" <+> quoteUntrimmed l | l <- ps ]
 
+-- | Render the paths which imports this config.
+docProjectImportedBy :: ProjectConfigPath -> Doc
+docProjectImportedBy (ProjectConfigPath (_ :| [])) = text ""
+docProjectImportedBy (ProjectConfigPath (_ :| ps)) = vcat $
+    [ text " " <+> text "imported by:" <+> quoteUntrimmed l | l <- ps ]
+
+
 -- | If the path has leading or trailing spaces then show it quoted.
 quoteUntrimmed :: FilePath -> Doc
 quoteUntrimmed s = if trim s /= s then quotes (text s) else text s
@@ -237,6 +246,9 @@ consProjectConfigPath p ps = ProjectConfigPath (p <| coerce ps)
 unconsProjectConfigPath :: ProjectConfigPath -> (FilePath, Maybe ProjectConfigPath)
 unconsProjectConfigPath ps = fmap ProjectConfigPath <$> NE.uncons (coerce ps)
 
+currentProjectConfigPath :: ProjectConfigPath -> FilePath
+currentProjectConfigPath (ProjectConfigPath (p :| _)) = p
+
 -- | Make paths relative to the directory of the root of the project, not
 -- relative to the file they were imported from.
 makeRelativeConfigPath :: FilePath -> ProjectConfigPath -> ProjectConfigPath
diff --git a/cabal-install-solver/src/Distribution/Solver/Types/Settings.hs b/cabal-install-solver/src/Distribution/Solver/Types/Settings.hs
index 4b7fe65b769..306c0c12185 100644
--- a/cabal-install-solver/src/Distribution/Solver/Types/Settings.hs
+++ b/cabal-install-solver/src/Distribution/Solver/Types/Settings.hs
@@ -105,3 +105,26 @@ instance Parsec OnlyConstrained where
     , P.string "none" >> return OnlyConstrainedNone
     ]
 
+instance Parsec ReorderGoals where
+  parsec = ReorderGoals <$> parsec
+
+instance Parsec CountConflicts where
+  parsec = CountConflicts <$> parsec
+
+instance Parsec FineGrainedConflicts where
+  parsec = FineGrainedConflicts <$> parsec
+
+instance Parsec MinimizeConflictSet where
+  parsec = MinimizeConflictSet <$> parsec
+
+instance Parsec StrongFlags where
+  parsec = StrongFlags <$> parsec
+
+instance Parsec AllowBootLibInstalls where
+  parsec = AllowBootLibInstalls <$> parsec
+
+instance Parsec PreferOldest where
+  parsec = PreferOldest <$> parsec
+
+instance Parsec IndependentGoals where
+  parsec = IndependentGoals <$> parsec
diff --git a/cabal-install/cabal-install.cabal b/cabal-install/cabal-install.cabal
index 8ace48c0a55..a8c97dab7fc 100644
--- a/cabal-install/cabal-install.cabal
+++ b/cabal-install/cabal-install.cabal
@@ -44,6 +44,11 @@ flag git-rev
   default: False
   manual: True
 
+flag legacy-comparison
+  description: Enable comparison between the new and legacy cabal.project parser
+  default: False
+  manual: True
+
 common warnings
     ghc-options:
       -Wall
@@ -131,6 +136,7 @@ library
         Distribution.Client.Dependency.Types
         Distribution.Client.DistDirLayout
         Distribution.Client.Errors
+        Distribution.Client.Errors.Parser
         Distribution.Client.Fetch
         Distribution.Client.FetchUtils
         Distribution.Client.FileMonitor
@@ -177,7 +183,10 @@ library
         Distribution.Client.ProjectBuilding.PackageFileMonitor
         Distribution.Client.ProjectBuilding.Types
         Distribution.Client.ProjectConfig
+        Distribution.Client.ProjectConfig.FieldGrammar
         Distribution.Client.ProjectConfig.Legacy
+        Distribution.Client.ProjectConfig.Lens
+        Distribution.Client.ProjectConfig.Parsec
         Distribution.Client.ProjectConfig.Types
         Distribution.Client.ProjectFlags
         Distribution.Client.ProjectOrchestration
@@ -225,6 +234,7 @@ library
         Distribution.Client.Upload
         Distribution.Client.Utils
         Distribution.Client.Utils.Json
+        Distribution.Client.Utils.Newtypes
         Distribution.Client.Utils.Parsec
         Distribution.Client.VCS
         Distribution.Client.Version
@@ -290,6 +300,9 @@ library
       build-depends: githash ^>= 0.1.7.0
       cpp-options: -DGIT_REV
 
+    if flag(legacy-comparison)
+      cpp-options: -DLEGACY_COMPARISON
+
 executable cabal
     import: warnings, base-dep
     main-is: Main.hs
@@ -378,6 +391,26 @@ test-suite unit-tests
       , tree-diff
       , QuickCheck >= 2.14.3 && <2.17
 
+-- Tests for the project file parser
+test-suite parser-tests
+    import: warnings, base-dep, cabal-dep, cabal-syntax-dep, cabal-install-solver-dep
+    default-language: Haskell2010
+    ghc-options: -rtsopts -threaded
+
+    type: exitcode-stdio-1.0
+    main-is: Tests.hs
+    hs-source-dirs: parser-tests
+    build-depends:
+      , cabal-install
+      , containers
+      , directory
+      , filepath
+      , network-uri >= 2.6.2.0 && <2.7
+      , tasty >= 1.2.3 && <1.6
+      , tasty-hunit >= 0.10
+    other-modules:
+      Tests.ParserTests
+
 -- Tests to run with a limited stack and heap size
 -- The test suite name must be keep short cause a longer one
 -- could make the build generating paths which exceeds the windows
diff --git a/cabal-install/parser-tests/Tests.hs b/cabal-install/parser-tests/Tests.hs
new file mode 100644
index 00000000000..f5655ad5389
--- /dev/null
+++ b/cabal-install/parser-tests/Tests.hs
@@ -0,0 +1,7 @@
+module Main where
+
+import Test.Tasty (defaultMain)
+import Tests.ParserTests (parserTests)
+
+main :: IO ()
+main = defaultMain parserTests
diff --git a/cabal-install/parser-tests/Tests/ParserTests.hs b/cabal-install/parser-tests/Tests/ParserTests.hs
new file mode 100644
index 00000000000..d9ab2f5247f
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/ParserTests.hs
@@ -0,0 +1,624 @@
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE RecordWildCards #-}
+
+-- | Tests for the project file parser
+module Tests.ParserTests (parserTests) where
+
+import Control.Monad.IO.Class
+  ( MonadIO (liftIO)
+  )
+import Data.Either (fromRight)
+import qualified Data.Map as Map
+import Data.Maybe (fromJust)
+import qualified Data.Set as Set
+import Distribution.Client.BuildReports.Types (ReportLevel (..))
+import Distribution.Client.CmdInstall.ClientInstallFlags (ClientInstallFlags (..))
+import Distribution.Client.Dependency.Types (PreSolver (..))
+import Distribution.Client.DistDirLayout
+import Distribution.Client.HttpUtils
+import Distribution.Client.IndexUtils.ActiveRepos (ActiveRepoEntry (..), ActiveRepos (..), CombineStrategy (..))
+import Distribution.Client.IndexUtils.IndexState (RepoIndexState (..), headTotalIndexState, insertIndexState)
+import Distribution.Client.ProjectConfig
+import Distribution.Client.RebuildMonad (runRebuild)
+import Distribution.Client.Targets (readUserConstraint)
+import Distribution.Client.Types.AllowNewer (AllowNewer (..), AllowOlder (..), RelaxDepMod (..), RelaxDepScope (..), RelaxDepSubject (..), RelaxDeps (..), RelaxedDep (..))
+import Distribution.Client.Types.InstallMethod (InstallMethod (..))
+import Distribution.Client.Types.OverwritePolicy (OverwritePolicy (..))
+import Distribution.Client.Types.Repo (LocalRepo (..), RemoteRepo (..), asPosixPath)
+import Distribution.Client.Types.RepoName (RepoName (..))
+import Distribution.Client.Types.SourceRepo
+import Distribution.Client.Types.WriteGhcEnvironmentFilesPolicy (WriteGhcEnvironmentFilesPolicy (..))
+import Distribution.Compat.Prelude
+import Distribution.Compiler (CompilerFlavor (..))
+import Distribution.Parsec (simpleParsec)
+import Distribution.Simple.Compiler (DebugInfoLevel (..), OptimisationLevel (..), PackageDBX (..), ProfDetailLevel (..))
+import Distribution.Simple.Flag
+import Distribution.Simple.InstallDirs (InstallDirs (..), toPathTemplate)
+import Distribution.Simple.Setup (DumpBuildInfo (..), HaddockTarget (..), TestShowDetails (..))
+import Distribution.Solver.Types.ConstraintSource (ConstraintSource (..))
+import Distribution.Solver.Types.ProjectConfigPath (ProjectConfigPath (..))
+import Distribution.Solver.Types.Settings
+  ( AllowBootLibInstalls (..)
+  , CountConflicts (..)
+  , FineGrainedConflicts (..)
+  , IndependentGoals (..)
+  , MinimizeConflictSet (..)
+  , OnlyConstrained (..)
+  , PreferOldest (..)
+  , ReorderGoals (..)
+  , StrongFlags (..)
+  )
+import Distribution.System (OS (..), buildOS)
+import Distribution.Types.CondTree (CondTree (..))
+import Distribution.Types.Flag (mkFlagAssignment)
+import Distribution.Types.PackageId (PackageIdentifier (..))
+import Distribution.Types.PackageName
+import Distribution.Types.PackageVersionConstraint (PackageVersionConstraint (..))
+import Distribution.Types.SourceRepo (KnownRepoType (..), RepoType (..))
+import Distribution.Types.Version (mkVersion)
+import Distribution.Types.VersionRange.Internal (VersionRange (..))
+import Distribution.Utils.NubList
+import Distribution.Verbosity
+import Network.URI (parseURI)
+import System.Directory (canonicalizePath, doesFileExist)
+import System.FilePath ((</>))
+import Prelude ()
+
+import Test.Tasty (TestTree, testGroup)
+import Test.Tasty.HUnit (Assertion, assertBool, assertEqual, testCase)
+
+parserTests :: TestTree
+parserTests =
+  testGroup
+    "project files parsec tests"
+    [ testCase "read packages" testPackages
+    , testCase "read optional-packages" testOptionalPackages
+    , testCase "read extra-packages" testExtraPackages
+    , testCase "read source-repository-package" testSourceRepoList
+    , testCase "read project-config-build-only" testProjectConfigBuildOnly
+    , testCase "read project-config-shared" testProjectConfigShared
+    , testCase "read install-dirs" testInstallDirs
+    , testCase "read remote-repos" testRemoteRepos
+    , testCase "read local-no-index-repos" testLocalNoIndexRepos
+    , testCase "set explicit provenance" testProjectConfigProvenance
+    , testCase "read project-config-local-packages" testProjectConfigLocalPackages
+    , testCase "read project-config-all-packages" testProjectConfigAllPackages
+    , testCase "read project-config-specific-packages" testProjectConfigSpecificPackages
+    , testCase "test projectConfigAllPackages concatenation" testAllPackagesConcat
+    , testCase "test projectConfigSpecificPackages concatenation" testSpecificPackagesConcat
+    , testCase "test program-locations concatenation" testProgramLocationsConcat
+    , testCase "test program-options concatenation" testProgramOptionsConcat
+    , testCase "test allow-newer and allow-older concatenation" testRelaxDepsConcat
+    , testCase "test library-coverage overwrites coverage" testLibraryCoverage
+    , testCase "test haddock-all flag" testHaddockAll
+    , testCase "test override haddock-all: True" testHaddockAllOverwriteTrue
+    , testCase "test override haddock-all: False" testHaddockAllOverwriteFalse
+    ]
+
+testPackages :: Assertion
+testPackages = do
+  let expected = [".", "packages/packages.cabal"]
+  (config, legacy) <- readConfigDefault "packages"
+  assertConfigEquals expected config legacy (projectPackages . condTreeData)
+
+testOptionalPackages :: Assertion
+testOptionalPackages = do
+  let expected = [".", "packages/packages.cabal"]
+  (config, legacy) <- readConfigDefault "optional-packages"
+  assertConfigEquals expected config legacy (projectPackagesOptional . condTreeData)
+
+testSourceRepoList :: Assertion
+testSourceRepoList = do
+  (config, legacy) <- readConfigDefault "source-repository-packages"
+  assertConfigEquals expected config legacy (projectPackagesRepo . condTreeData)
+  where
+    expected =
+      [ SourceRepositoryPackage
+          { srpType = KnownRepoType Git
+          , srpLocation = "https://example.com/Project.git"
+          , srpTag = Just "1234"
+          , srpBranch = Nothing
+          , srpSubdir = []
+          , srpCommand = []
+          }
+      , SourceRepositoryPackage
+          { srpType = KnownRepoType Git
+          , srpLocation = "https://example.com/example-dir/"
+          , srpTag = Just "12345"
+          , srpBranch = Nothing
+          , srpSubdir = ["subproject"]
+          , srpCommand = []
+          }
+      ]
+
+testExtraPackages :: Assertion
+testExtraPackages = do
+  (config, legacy) <- readConfigDefault "extra-packages"
+  assertConfigEquals expected config legacy (projectPackagesNamed . condTreeData)
+  where
+    expected =
+      [ PackageVersionConstraint (mkPackageName "a") (OrLaterVersion (mkVersion [0]))
+      , PackageVersionConstraint (mkPackageName "b") (IntersectVersionRanges (OrLaterVersion (mkVersion [0, 7, 3])) (EarlierVersion (mkVersion [0, 9])))
+      ]
+
+testProjectConfigBuildOnly :: Assertion
+testProjectConfigBuildOnly = do
+  (config, legacy) <- readConfigDefault "project-config-build-only"
+  assertConfigEquals expected config legacy (projectConfigBuildOnly . condTreeData)
+  where
+    expected = ProjectConfigBuildOnly{..}
+    projectConfigVerbosity = toFlag (toEnum 2)
+    projectConfigDryRun = mempty -- cli only
+    projectConfigOnlyDeps = mempty -- cli only
+    projectConfigOnlyDownload = mempty -- cli only
+    projectConfigSummaryFile = toNubList [toPathTemplate "summaryFile", toPathTemplate "summaryFile2"]
+    projectConfigLogFile = toFlag $ toPathTemplate "myLog.log"
+    projectConfigBuildReports = toFlag DetailedReports
+    projectConfigReportPlanningFailure = toFlag True
+    projectConfigSymlinkBinDir = toFlag "some-bindir"
+    projectConfigNumJobs = toFlag $ Just 4
+    projectConfigUseSemaphore = toFlag True
+    projectConfigKeepGoing = toFlag True
+    projectConfigOfflineMode = toFlag True
+    projectConfigKeepTempFiles = toFlag True
+    projectConfigHttpTransport = toFlag "wget"
+    projectConfigIgnoreExpiry = toFlag True
+    projectConfigCacheDir = toFlag "some-cache-dir"
+    projectConfigLogsDir = toFlag "logs-directory"
+    projectConfigClientInstallFlags =
+      ClientInstallFlags
+        { cinstInstallLibs = Flag True
+        , cinstEnvironmentPath = Flag "path/to/env"
+        , cinstOverwritePolicy = Flag AlwaysOverwrite
+        , cinstInstallMethod = Flag InstallMethodSymlink
+        , cinstInstalldir = Flag "path/to/installdir"
+        }
+
+testProjectConfigShared :: Assertion
+testProjectConfigShared = do
+  (config, legacy) <- readConfigDefault "project-config-shared"
+  assertConfigEquals expected config legacy (projectConfigShared . condTreeData)
+  where
+    expected = ProjectConfigShared{..}
+    projectConfigDistDir = toFlag "something"
+    projectConfigConfigFile = mempty -- cli only
+    projectConfigProjectFileParser = mempty -- cli only
+    projectConfigProjectDir = toFlag "my-project-dir"
+    projectConfigProjectFile = toFlag "my-project"
+    projectConfigIgnoreProject = toFlag False
+    projectConfigHcFlavor = toFlag GHCJS
+    projectConfigHcPath = toFlag "/some/path/to/compiler"
+    projectConfigHcPkg = toFlag "/some/path/to/ghc-pkg"
+    projectConfigHaddockIndex = toFlag $ toPathTemplate "/path/to/haddock-index"
+    projectConfigInstallDirs = mempty -- tested below in testInstallDirs
+    projectConfigPackageDBs = [Nothing, Just (SpecificPackageDB "foo"), Nothing, Just (SpecificPackageDB "bar"), Just (SpecificPackageDB "baz")]
+    projectConfigRemoteRepos = mempty -- tested below in testRemoteRepos
+    projectConfigLocalNoIndexRepos = mempty -- tested below in testLocalNoIndexRepos
+    projectConfigActiveRepos = Flag (ActiveRepos [ActiveRepo (RepoName "hackage.haskell.org") CombineStrategyMerge, ActiveRepo (RepoName "my-repository") CombineStrategyOverride])
+    projectConfigIndexState =
+      let
+        hackageState = IndexStateTime $ fromJust $ simpleParsec "2020-05-06T22:33:27Z"
+        indexState' = insertIndexState (RepoName "hackage.haskell.org") hackageState headTotalIndexState
+        headHackageState = IndexStateTime $ fromJust $ simpleParsec "2020-04-29T04:11:05Z"
+        indexState'' = insertIndexState (RepoName "head.hackage") headHackageState indexState'
+       in
+        toFlag indexState''
+    projectConfigStoreDir = toFlag "a/store/dir/path" -- cli only
+    projectConfigConstraints =
+      let
+        bar = fromRight (error "error parsing bar") $ readUserConstraint "bar == 2.1"
+        barFlags = fromRight (error "error parsing bar flags") $ readUserConstraint "bar +foo -baz"
+        source = ConstraintSourceProjectConfig $ ProjectConfigPath $ "cabal.project" :| []
+       in
+        [(bar, source), (barFlags, source)]
+    projectConfigPreferences = [PackageVersionConstraint (mkPackageName "foo") (ThisVersion (mkVersion [0, 9])), PackageVersionConstraint (mkPackageName "baz") (LaterVersion (mkVersion [2, 0]))]
+    projectConfigCabalVersion = Flag (mkVersion [1, 24, 0, 1])
+    projectConfigSolver = Flag AlwaysModular
+    projectConfigAllowOlder = Just (AllowOlder $ RelaxDepsSome [RelaxedDep RelaxDepScopeAll RelaxDepModNone (RelaxDepSubjectPkg (mkPackageName "dep")), RelaxedDep (RelaxDepScopePackageId (PackageIdentifier (mkPackageName "pkga") (mkVersion [1, 1, 2]))) RelaxDepModNone (RelaxDepSubjectPkg (mkPackageName "dep-pkg"))])
+    projectConfigAllowNewer = Just (AllowNewer $ RelaxDepsSome [RelaxedDep (RelaxDepScopePackageId (PackageIdentifier (mkPackageName "pkgb") (mkVersion [1, 2, 3]))) RelaxDepModNone (RelaxDepSubjectPkg (mkPackageName "dep-pkgb")), RelaxedDep RelaxDepScopeAll RelaxDepModNone (RelaxDepSubjectPkg (mkPackageName "importantlib"))])
+    projectConfigWriteGhcEnvironmentFilesPolicy = Flag AlwaysWriteGhcEnvironmentFiles
+    projectConfigMaxBackjumps = toFlag 42
+    projectConfigReorderGoals = Flag (ReorderGoals True)
+    projectConfigCountConflicts = Flag (CountConflicts False)
+    projectConfigFineGrainedConflicts = Flag (FineGrainedConflicts False)
+    projectConfigMinimizeConflictSet = Flag (MinimizeConflictSet True)
+    projectConfigStrongFlags = Flag (StrongFlags True)
+    projectConfigAllowBootLibInstalls = Flag (AllowBootLibInstalls True)
+    projectConfigOnlyConstrained = Flag OnlyConstrainedAll
+    projectConfigPerComponent = Flag True
+    projectConfigIndependentGoals = Flag (IndependentGoals True)
+    projectConfigPreferOldest = Flag (PreferOldest True)
+    projectConfigProgPathExtra = toNubList ["/foo/bar", "/baz/quux"]
+    projectConfigMultiRepl = toFlag True
+
+testInstallDirs :: Assertion
+testInstallDirs = do
+  (config, legacy) <- readConfigDefault "install-dirs"
+  assertConfigEquals expected config legacy (projectConfigInstallDirs . projectConfigShared . condTreeData)
+  where
+    expected =
+      InstallDirs
+        { prefix = Flag $ toPathTemplate "my/prefix-path"
+        , bindir = Flag $ toPathTemplate "bin/dir/"
+        , libdir = Flag $ toPathTemplate "lib/dir/path"
+        , libsubdir = Flag $ toPathTemplate "/lib/sub/dir"
+        , dynlibdir = Flag $ toPathTemplate "dyn/lib/dir/path"
+        , flibdir = mempty
+        , libexecdir = Flag $ toPathTemplate "lib/exec/dir/"
+        , libexecsubdir = Flag $ toPathTemplate "libexec/subdir"
+        , includedir = mempty
+        , datadir = Flag $ toPathTemplate "path/to/datadir/"
+        , datasubdir = Flag $ toPathTemplate "a/datadir/subdir"
+        , docdir = Flag $ toPathTemplate "path/to/docs"
+        , mandir = mempty
+        , htmldir = Flag $ toPathTemplate "dir/html/"
+        , haddockdir = Flag $ toPathTemplate "haddock/dir"
+        , sysconfdir = Flag $ toPathTemplate "sys/conf/dir"
+        }
+
+testRemoteRepos :: Assertion
+testRemoteRepos = do
+  (config, legacy) <- readConfigDefault "remote-repos"
+  let actualRemoteRepos = (fromNubList . projectConfigRemoteRepos . projectConfigShared . condTreeData) config
+  assertBool "Expected RemoteRepos do not match parsed values" $ compareLists expected actualRemoteRepos compareRemoteRepos
+  assertConfigEquals mempty config legacy (projectConfigLocalNoIndexRepos . projectConfigShared . condTreeData)
+  where
+    expected = [packagesRepository, morePackagesRepository, secureLocalRepository]
+    packagesRepository =
+      RemoteRepo
+        { remoteRepoName = RepoName "packages.example.org"
+        , remoteRepoURI = fromJust $ parseURI "http://packages.example.org/"
+        , remoteRepoSecure = pure True
+        , remoteRepoRootKeys = ["21", "42"]
+        , remoteRepoKeyThreshold = 2
+        , remoteRepoShouldTryHttps = False
+        }
+    morePackagesRepository =
+      RemoteRepo
+        { remoteRepoName = RepoName "more-packages.example.org"
+        , remoteRepoURI = fromJust $ parseURI "https://more-packages.example.org/"
+        , remoteRepoSecure = pure True
+        , remoteRepoRootKeys = ["foo", "bar"]
+        , remoteRepoKeyThreshold = 1
+        , remoteRepoShouldTryHttps = False
+        }
+    secureLocalRepository =
+      RemoteRepo
+        { remoteRepoName = RepoName "my-secure-local-repository"
+        , remoteRepoURI = fromJust $ parseURI "file:/path/to/secure/repo"
+        , remoteRepoSecure = pure True
+        , remoteRepoRootKeys = ["123"]
+        , remoteRepoKeyThreshold = 1
+        , remoteRepoShouldTryHttps = False
+        }
+
+testLocalNoIndexRepos :: Assertion
+testLocalNoIndexRepos = do
+  (config, legacy) <- readConfigDefault "local-no-index-repos"
+  let actualLocalRepos = (fromNubList . projectConfigLocalNoIndexRepos . projectConfigShared . condTreeData) config
+  assertBool "Expected LocalNoIndexRepos do not match parsed values" $ compareLists expected actualLocalRepos compareLocalRepos
+  assertConfigEquals mempty config legacy (projectConfigRemoteRepos . projectConfigShared . condTreeData)
+  where
+    expected = [myRepository, mySecureRepository]
+    myRepository =
+      LocalRepo
+        { localRepoName = RepoName "my-repository"
+        , localRepoPath = normalisePath "/absolute/path/to/directory"
+        , localRepoSharedCache = False
+        }
+    mySecureRepository =
+      LocalRepo
+        { localRepoName = RepoName "my-other-repository"
+        , localRepoPath = normalisePath "/another/path/to/repository"
+        , localRepoSharedCache = False
+        }
+    normalisePath path = case buildOS of
+      Windows -> asPosixPath path
+      _ -> path
+
+testProjectConfigProvenance :: Assertion
+testProjectConfigProvenance = do
+  let expected = Set.singleton (Explicit (ProjectConfigPath $ "cabal.project" :| []))
+  (config, legacy) <- readConfigDefault "empty"
+  assertConfigEquals expected config legacy (projectConfigProvenance . condTreeData)
+
+testProjectConfigLocalPackages :: Assertion
+testProjectConfigLocalPackages = do
+  (config, legacy) <- readConfigDefault "project-config-local-packages"
+  assertConfigEquals expected config legacy (projectConfigLocalPackages . condTreeData)
+  where
+    expected = PackageConfig{..}
+    packageConfigProgramPaths = MapLast $ Map.fromList [("ghc", "/tmp/bin/ghc"), ("gcc", "/tmp/bin/gcc")]
+    packageConfigProgramArgs = MapMappend $ Map.fromList [("ghc", ["-fno-state-hack", "-foo"]), ("gcc", ["-baz", "-quux"])]
+    packageConfigProgramPathExtra = toNubList ["/tmp/bin/extra", "/usr/local/bin"]
+    packageConfigFlagAssignment = mkFlagAssignment [("foo", True), ("bar", False)]
+    packageConfigVanillaLib = Flag False
+    packageConfigSharedLib = Flag True
+    packageConfigStaticLib = Flag True
+    packageConfigDynExe = Flag True
+    packageConfigFullyStaticExe = Flag True
+    packageConfigProf = Flag True
+    packageConfigProfLib = Flag True
+    packageConfigProfShared = Flag False
+    packageConfigProfExe = Flag True
+    packageConfigProfDetail = Flag ProfDetailAllFunctions
+    packageConfigProfLibDetail = Flag ProfDetailExportedFunctions
+    packageConfigConfigureArgs = ["-some-arg", "/some/path"]
+    packageConfigOptimization = Flag MaximumOptimisation
+    packageConfigProgPrefix = Flag $ toPathTemplate "another/path"
+    packageConfigProgSuffix = Flag $ toPathTemplate "and/another/path"
+    packageConfigExtraLibDirs = ["so", "many", "lib/dirs"]
+    packageConfigExtraLibDirsStatic = ["a/few", "static/lib/dirs"]
+    packageConfigExtraFrameworkDirs = ["osx/framework", "dirs"]
+    packageConfigExtraIncludeDirs = ["incredible/amount", "of", "include", "directories"]
+    packageConfigGHCiLib = Flag False
+    packageConfigSplitSections = Flag True
+    packageConfigSplitObjs = Flag True
+    packageConfigStripExes = Flag False
+    packageConfigStripLibs = Flag False
+    packageConfigTests = Flag True
+    packageConfigBenchmarks = Flag True
+    packageConfigCoverage = Flag True
+    packageConfigRelocatable = Flag True
+    packageConfigDebugInfo = Flag MaximalDebugInfo
+    packageConfigDumpBuildInfo = Flag DumpBuildInfo
+    packageConfigRunTests = Flag True
+    packageConfigDocumentation = Flag True
+    -- Haddock options
+    packageConfigHaddockHoogle = Flag True
+    packageConfigHaddockHtml = Flag False
+    packageConfigHaddockHtmlLocation = Flag "http://hackage.haskell.org/packages/archive/$pkg/latest/doc/html"
+    packageConfigHaddockForeignLibs = Flag True
+    packageConfigHaddockExecutables = Flag True
+    packageConfigHaddockTestSuites = Flag True
+    packageConfigHaddockBenchmarks = Flag True
+    packageConfigHaddockInternal = Flag True
+    packageConfigHaddockCss = Flag "some/path/to/file.css"
+    packageConfigHaddockLinkedSource = Flag True
+    packageConfigHaddockQuickJump = Flag True
+    packageConfigHaddockHscolourCss = Flag "another/path/to/hscolour.css"
+    packageConfigHaddockContents = Flag $ toPathTemplate "https://example.com/$pkg/contents"
+    packageConfigHaddockIndex = Flag $ toPathTemplate "separately-generated/HTML/index"
+    packageConfigHaddockBaseUrl = Flag "https://example.com/haddock-base-url"
+    packageConfigHaddockResourcesDir = Flag "/haddock/static"
+    packageConfigHaddockOutputDir = Flag "/haddock/output"
+    packageConfigHaddockUseUnicode = Flag False
+    packageConfigHaddockForHackage = Flag ForHackage
+    packageConfigTestHumanLog = Flag $ toPathTemplate "human-log.log"
+    packageConfigTestMachineLog = Flag $ toPathTemplate "machine.log"
+    packageConfigTestShowDetails = Flag Streaming
+    packageConfigTestKeepTix = Flag True
+    packageConfigTestWrapper = Flag "/test-wrapper-path/"
+    packageConfigTestFailWhenNoTestSuites = Flag True
+    packageConfigTestTestOptions = [toPathTemplate "--some-option", toPathTemplate "42"]
+    packageConfigBenchmarkOptions = [toPathTemplate "--some-benchmark-option", toPathTemplate "--another-option"]
+
+testProjectConfigAllPackages :: Assertion
+testProjectConfigAllPackages = do
+  (config, legacy) <- readConfigDefault "project-config-all-packages"
+  assertConfigEquals expected config legacy (projectConfigAllPackages . condTreeData)
+  where
+    expected :: PackageConfig
+    expected =
+      mempty
+        { packageConfigProfDetail = Flag ProfDetailAllFunctions
+        , packageConfigProfLibDetail = Flag ProfDetailExportedFunctions
+        }
+
+testProjectConfigSpecificPackages :: Assertion
+testProjectConfigSpecificPackages = do
+  (config, legacy) <- readConfigDefault "project-config-specific-packages"
+  assertConfigEquals expected config legacy (projectConfigSpecificPackage . condTreeData)
+  where
+    expected = MapMappend $ Map.fromList [("foo", expectedFoo), ("bar", expectedBar), ("baz", expectedBaz)]
+    expectedFoo :: PackageConfig
+    expectedFoo =
+      mempty
+        { packageConfigProfDetail = Flag ProfDetailAllFunctions
+        , packageConfigProfLibDetail = Flag ProfDetailExportedFunctions
+        , packageConfigVanillaLib = Flag True
+        }
+    expectedBar :: PackageConfig
+    expectedBar =
+      mempty
+        { packageConfigProfDetail = Flag ProfDetailTopLate
+        , packageConfigProfLibDetail = Flag ProfDetailNone
+        , packageConfigProgPrefix = Flag $ toPathTemplate "prefix/path"
+        }
+    expectedBaz :: PackageConfig
+    expectedBaz =
+      mempty
+        { packageConfigSharedLib = Flag True
+        }
+
+testAllPackagesConcat :: Assertion
+testAllPackagesConcat = do
+  (config, legacy) <- readConfigDefault "all-packages-concat"
+  assertConfigEquals expected config legacy (projectConfigAllPackages . condTreeData)
+  where
+    expected :: PackageConfig
+    expected =
+      mempty
+        { packageConfigSharedLib = Flag True
+        , packageConfigStaticLib = Flag True
+        , packageConfigProgramArgs =
+            MapMappend $
+              Map.fromList
+                [ ("ghc", ["-fwarn-tabs", "-optc-fno-builtin-malloc", "-Wall", "-optc-fno-builtin-realloc", "-fwrite-ide-info"])
+                ]
+        }
+
+testSpecificPackagesConcat :: Assertion
+testSpecificPackagesConcat = do
+  (config, legacy) <- readConfigDefault "specific-packages-concat"
+  assertConfigEquals expected config legacy (projectConfigSpecificPackage . condTreeData)
+  where
+    expected = MapMappend $ Map.fromList [("foo", expectedFoo)]
+    expectedFoo :: PackageConfig
+    expectedFoo =
+      mempty
+        { packageConfigSharedLib = Flag True
+        , packageConfigStaticLib = Flag True
+        , packageConfigProgramArgs = MapMappend $ Map.fromList [("ghc", ["-fno-state-hack", "-threaded"])]
+        }
+
+testProgramLocationsConcat :: Assertion
+testProgramLocationsConcat = do
+  (config, legacy) <- readConfigDefault "program-locations-concat"
+  assertConfigEquals expected config legacy (projectConfigLocalPackages . condTreeData)
+  where
+    expected :: PackageConfig
+    expected =
+      mempty
+        { packageConfigProgramPaths = MapLast $ Map.fromList [("gcc", "/tmp/bin/gcc"), ("ghc", "/tmp/bin/ghc")]
+        }
+
+testProgramOptionsConcat :: Assertion
+testProgramOptionsConcat = do
+  (config, legacy) <- readConfigDefault "program-options-concat"
+  assertConfigEquals expected config legacy (projectConfigLocalPackages . condTreeData)
+  where
+    expected :: PackageConfig
+    expected =
+      mempty
+        { packageConfigProgramArgs =
+            MapMappend $
+              Map.fromList
+                [ ("ghc", ["-threaded", "-Wall", "-fno-state-hack"])
+                , ("gcc", ["-baz", "-foo", "-bar"])
+                , ("haddock", ["--optghc=-optP -P"])
+                , ("ld", ["-Wl,--gc-sections"])
+                ]
+        }
+
+testRelaxDepsConcat :: Assertion
+testRelaxDepsConcat = do
+  (config, legacy) <- readConfigDefault "relax-deps-concat"
+  assertConfigEquals expectedAllowNewer config legacy (projectConfigAllowNewer . projectConfigShared . condTreeData)
+  assertConfigEquals expectedAllowOlder config legacy (projectConfigAllowOlder . projectConfigShared . condTreeData)
+  where
+    expectedAllowNewer :: Maybe AllowNewer
+    expectedAllowNewer =
+      pure $
+        AllowNewer $
+          RelaxDepsSome
+            [ RelaxedDep (RelaxDepScopePackageId (PackageIdentifier (mkPackageName "cassava") (mkVersion [0, 5, 2, 0]))) RelaxDepModNone (RelaxDepSubjectPkg (mkPackageName "base"))
+            , RelaxedDep (RelaxDepScopePackageId (PackageIdentifier (mkPackageName "vector-th-unbox") (mkVersion [0, 2, 1, 7]))) RelaxDepModNone (RelaxDepSubjectPkg (mkPackageName "base"))
+            , RelaxedDep (RelaxDepScopePackageId (PackageIdentifier (mkPackageName "vector-th-unbox") (mkVersion [0, 2, 1, 7]))) RelaxDepModNone (RelaxDepSubjectPkg (mkPackageName "template-haskell"))
+            ]
+    expectedAllowOlder :: Maybe AllowOlder
+    expectedAllowOlder =
+      pure $
+        AllowOlder $
+          RelaxDepsSome
+            [ RelaxedDep (RelaxDepScopePackageId (PackageIdentifier (mkPackageName "mtl") (mkVersion [2, 3, 1]))) RelaxDepModNone (RelaxDepSubjectPkg (mkPackageName "base"))
+            , RelaxedDep (RelaxDepScopePackageId (PackageIdentifier (mkPackageName "aeson") (mkVersion [2, 2, 3, 0]))) RelaxDepModNone (RelaxDepSubjectPkg (mkPackageName "bytestring"))
+            , RelaxedDep (RelaxDepScopePackageId (PackageIdentifier (mkPackageName "containers") (mkVersion [0, 7]))) RelaxDepModNone (RelaxDepSubjectPkg (mkPackageName "array"))
+            ]
+
+-- | Tests that if both library-coverage and coverage flags are specified, library-coverage is used.
+testLibraryCoverage :: Assertion
+testLibraryCoverage = do
+  (config, legacy) <- readConfigDefault "library-coverage"
+  assertConfigEquals (Flag False) config legacy (packageConfigCoverage . projectConfigLocalPackages . condTreeData)
+
+testHaddockAll :: Assertion
+testHaddockAll = do
+  (config, legacy) <- readConfigDefault "haddock-all"
+  assertConfigEquals (Flag True) config legacy (packageConfigHaddockExecutables . projectConfigLocalPackages . condTreeData)
+  assertConfigEquals (Flag True) config legacy (packageConfigHaddockTestSuites . projectConfigLocalPackages . condTreeData)
+  assertConfigEquals (Flag True) config legacy (packageConfigHaddockBenchmarks . projectConfigLocalPackages . condTreeData)
+  assertConfigEquals (Flag True) config legacy (packageConfigHaddockForeignLibs . projectConfigLocalPackages . condTreeData)
+
+-- | Tests that an explicitly set field can override a value inherited from haddock-all.
+testHaddockAllOverwriteTrue :: Assertion
+testHaddockAllOverwriteTrue = do
+  (config, legacy) <- readConfigDefault "haddock-all-overwrite-true"
+  assertConfigEquals (Flag True) config legacy (packageConfigHaddockExecutables . projectConfigLocalPackages . condTreeData)
+  assertConfigEquals (Flag True) config legacy (packageConfigHaddockTestSuites . projectConfigLocalPackages . condTreeData)
+  assertConfigEquals (Flag True) config legacy (packageConfigHaddockBenchmarks . projectConfigLocalPackages . condTreeData)
+  assertConfigEquals (Flag False) config legacy (packageConfigHaddockForeignLibs . projectConfigLocalPackages . condTreeData)
+
+testHaddockAllOverwriteFalse :: Assertion
+testHaddockAllOverwriteFalse = do
+  (config, legacy) <- readConfigDefault "haddock-all-overwrite-false"
+  assertConfigEquals (Flag True) config legacy (packageConfigHaddockExecutables . projectConfigLocalPackages . condTreeData)
+  assertConfigEquals (Flag False) config legacy (packageConfigHaddockTestSuites . projectConfigLocalPackages . condTreeData)
+  assertConfigEquals (Flag False) config legacy (packageConfigHaddockBenchmarks . projectConfigLocalPackages . condTreeData)
+  assertConfigEquals (Flag False) config legacy (packageConfigHaddockForeignLibs . projectConfigLocalPackages . condTreeData)
+
+-------------------------------------------------------------------------------
+-- Test Utilities
+-------------------------------------------------------------------------------
+baseDir :: FilePath
+baseDir = "parser-tests" </> "Tests" </> "files"
+
+verbosity :: Verbosity
+verbosity = normal
+
+readConfigDefault :: FilePath -> IO (ProjectConfigSkeleton, ProjectConfigSkeleton)
+readConfigDefault testSubDir = readConfig testSubDir "cabal.project"
+
+readConfig :: FilePath -> FilePath -> IO (ProjectConfigSkeleton, ProjectConfigSkeleton)
+readConfig testSubDir projectFileName = do
+  (TestDir testRootFp projectConfigFp distDirLayout) <- testDirInfo testSubDir projectFileName
+  exists <- liftIO $ doesFileExist projectConfigFp
+  assertBool ("projectConfig does not exist: " <> projectConfigFp) exists
+  httpTransport <- liftIO $ configureTransport verbosity [] Nothing
+  let extensionName = ""
+      extensionDescription = ""
+  parsec <-
+    liftIO $
+      runRebuild testRootFp $
+        readProjectFileSkeletonParsec verbosity httpTransport distDirLayout extensionName extensionDescription
+  legacy <-
+    liftIO $
+      runRebuild testRootFp $
+        readProjectFileSkeletonLegacy verbosity httpTransport distDirLayout extensionName extensionDescription
+  return (parsec, legacy)
+
+assertConfigEquals :: (Eq a, Show a) => a -> ProjectConfigSkeleton -> ProjectConfigSkeleton -> (ProjectConfigSkeleton -> a) -> Assertion
+assertConfigEquals expected config configLegacy access = do
+  assertEqual "Expectation does not match result of Legacy parser" expected actualLegacy
+  assertEqual "Parsed Config does not match expected" expected actual
+  where
+    actual = access config
+    actualLegacy = access configLegacy
+
+-- | Represents the directory structure and associated file paths for a test
+data TestDir = TestDir
+  { _testDirTestRootFp :: FilePath
+  -- ^ Every test has a root directory in ./files/<test-title>
+  , _testDirProjectConfigFp :: FilePath
+  -- ^ Every test has a project config in testDirTestRootFp/cabal.project
+  , _testDirDistDirLayout :: DistDirLayout
+  }
+
+testDirInfo :: FilePath -> FilePath -> IO TestDir
+testDirInfo testSubDir projectFileName = do
+  projectRootDir <- canonicalizePath (baseDir </> testSubDir)
+  let
+    projectRoot = ProjectRootExplicit projectRootDir projectFileName
+    distDirLayout = defaultDistDirLayout projectRoot Nothing Nothing
+    extensionName = ""
+    projectConfigFp = distProjectFile distDirLayout extensionName
+  return $ TestDir projectRootDir projectConfigFp distDirLayout
+
+-- | Compares two lists element-wise using a comparison function.
+compareLists :: [a] -> [a] -> (a -> a -> Bool) -> Bool
+compareLists xs ys compare' = length xs == length ys && all (uncurry compare') (zip xs ys)
+
+-- | Compares LocalRepos ignoring field 'localRepoSharedCache' because we do not parse it.
+compareLocalRepos :: LocalRepo -> LocalRepo -> Bool
+compareLocalRepos repo1 repo2 =
+  localRepoName repo1 == localRepoName repo2
+    && localRepoPath repo1 == localRepoPath repo2
+
+-- | Compares RemoteRepos ignoring field 'remoteRepoShouldTryHttps' because we do not parse it.
+compareRemoteRepos :: RemoteRepo -> RemoteRepo -> Bool
+compareRemoteRepos repo1 repo2 =
+  remoteRepoName repo1 == remoteRepoName repo2
+    && remoteRepoURI repo1 == remoteRepoURI repo2
+    && remoteRepoSecure repo1 == remoteRepoSecure repo2
+    && remoteRepoRootKeys repo1 == remoteRepoRootKeys repo2
+    && remoteRepoKeyThreshold repo1 == remoteRepoKeyThreshold repo2
diff --git a/cabal-install/parser-tests/Tests/files/all-packages-concat/cabal.project b/cabal-install/parser-tests/Tests/files/all-packages-concat/cabal.project
new file mode 100644
index 00000000000..a85e19b9868
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/files/all-packages-concat/cabal.project
@@ -0,0 +1,8 @@
+package *
+    static: True
+    ghc-options: -fwrite-ide-info
+    ghc-options: -Wall -optc-fno-builtin-realloc
+
+package *
+    shared: True
+    ghc-options: -fwarn-tabs -optc-fno-builtin-malloc
diff --git a/cabal-install/parser-tests/Tests/files/empty/cabal.project b/cabal-install/parser-tests/Tests/files/empty/cabal.project
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/cabal-install/parser-tests/Tests/files/extra-packages/cabal.project b/cabal-install/parser-tests/Tests/files/extra-packages/cabal.project
new file mode 100644
index 00000000000..13d55f2ef33
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/files/extra-packages/cabal.project
@@ -0,0 +1,3 @@
+extra-packages:
+        a
+        , b     >= 0.7.3    && < 0.9,
diff --git a/cabal-install/parser-tests/Tests/files/haddock-all-overwrite-false/cabal.project b/cabal-install/parser-tests/Tests/files/haddock-all-overwrite-false/cabal.project
new file mode 100644
index 00000000000..c0c044081b6
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/files/haddock-all-overwrite-false/cabal.project
@@ -0,0 +1,2 @@
+haddock-all: False
+haddock-executables: True
diff --git a/cabal-install/parser-tests/Tests/files/haddock-all-overwrite-true/cabal.project b/cabal-install/parser-tests/Tests/files/haddock-all-overwrite-true/cabal.project
new file mode 100644
index 00000000000..c591d86a961
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/files/haddock-all-overwrite-true/cabal.project
@@ -0,0 +1,2 @@
+haddock-all: True
+haddock-foreign-libraries: False
diff --git a/cabal-install/parser-tests/Tests/files/haddock-all/cabal.project b/cabal-install/parser-tests/Tests/files/haddock-all/cabal.project
new file mode 100644
index 00000000000..275c4539524
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/files/haddock-all/cabal.project
@@ -0,0 +1 @@
+haddock-all: True
diff --git a/cabal-install/parser-tests/Tests/files/install-dirs/cabal.project b/cabal-install/parser-tests/Tests/files/install-dirs/cabal.project
new file mode 100644
index 00000000000..e9397c1bbef
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/files/install-dirs/cabal.project
@@ -0,0 +1,13 @@
+prefix: my/prefix-path
+bindir: bin/dir/
+libdir: lib/dir/path
+libsubdir: /lib/sub/dir
+dynlibdir: dyn/lib/dir/path
+libexecdir: lib/exec/dir/
+libexecsubdir: libexec/subdir
+datadir: path/to/datadir/
+datasubdir: a/datadir/subdir
+docdir: path/to/docs
+htmldir: dir/html/
+haddockdir: haddock/dir
+sysconfdir: sys/conf/dir
diff --git a/cabal-install/parser-tests/Tests/files/library-coverage/cabal.project b/cabal-install/parser-tests/Tests/files/library-coverage/cabal.project
new file mode 100644
index 00000000000..074a06e7731
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/files/library-coverage/cabal.project
@@ -0,0 +1,2 @@
+library-coverage: False
+coverage: True
diff --git a/cabal-install/parser-tests/Tests/files/local-no-index-repos/cabal.project b/cabal-install/parser-tests/Tests/files/local-no-index-repos/cabal.project
new file mode 100644
index 00000000000..f6b42df28b6
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/files/local-no-index-repos/cabal.project
@@ -0,0 +1,5 @@
+repository my-repository
+  url: file+noindex:///absolute/path/to/directory
+
+repository my-other-repository
+  url: file+noindex:/another/path/to/repository
diff --git a/cabal-install/parser-tests/Tests/files/optional-packages/cabal.project b/cabal-install/parser-tests/Tests/files/optional-packages/cabal.project
new file mode 100644
index 00000000000..37e21016d6a
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/files/optional-packages/cabal.project
@@ -0,0 +1 @@
+optional-packages: . packages/packages.cabal
diff --git a/cabal-install/parser-tests/Tests/files/packages/cabal.project b/cabal-install/parser-tests/Tests/files/packages/cabal.project
new file mode 100644
index 00000000000..6d9d4728a55
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/files/packages/cabal.project
@@ -0,0 +1 @@
+packages: . packages/packages.cabal
diff --git a/cabal-install/parser-tests/Tests/files/program-locations-concat/cabal.project b/cabal-install/parser-tests/Tests/files/program-locations-concat/cabal.project
new file mode 100644
index 00000000000..95657d95a17
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/files/program-locations-concat/cabal.project
@@ -0,0 +1,5 @@
+program-locations
+    gcc-location: /tmp/bin/gcc
+
+program-locations
+    ghc-location: /tmp/bin/ghc
diff --git a/cabal-install/parser-tests/Tests/files/program-options-concat/cabal.project b/cabal-install/parser-tests/Tests/files/program-options-concat/cabal.project
new file mode 100644
index 00000000000..a418091c0d5
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/files/program-options-concat/cabal.project
@@ -0,0 +1,9 @@
+program-options
+    ghc-options: -fno-state-hack
+    gcc-options: -foo -bar
+    haddock-options: --optghc="-optP -P"
+
+program-options
+    ghc-options: -threaded -Wall
+    gcc-options: -baz
+    ld-options: -Wl,--gc-sections
diff --git a/cabal-install/parser-tests/Tests/files/project-config-all-packages/cabal.project b/cabal-install/parser-tests/Tests/files/project-config-all-packages/cabal.project
new file mode 100644
index 00000000000..2b336cf830c
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/files/project-config-all-packages/cabal.project
@@ -0,0 +1,3 @@
+package *
+    profiling-detail: all-functions
+    library-profiling-detail: exported-functions
diff --git a/cabal-install/parser-tests/Tests/files/project-config-build-only/cabal.project b/cabal-install/parser-tests/Tests/files/project-config-build-only/cabal.project
new file mode 100644
index 00000000000..eac06d8aadd
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/files/project-config-build-only/cabal.project
@@ -0,0 +1,22 @@
+verbose: 2
+build-summary: summaryFile, summaryFile2
+build-log: myLog.log
+remote-build-reporting: detailed
+report-planning-failure: True
+symlink-bindir: some-bindir
+jobs: 4
+semaphore: True
+keep-going: True
+offline: True
+haddock-keep-temp-files:  True
+http-transport: wget
+ignore-expiry: True
+remote-repo-cache: some-cache-dir
+logs-dir: logs-directory
+
+-- clientInstallFlags
+lib: True
+package-env: path/to/env
+overwrite-policy: always
+install-method: symlink
+installdir: path/to/installdir
diff --git a/cabal-install/parser-tests/Tests/files/project-config-local-packages/cabal.project b/cabal-install/parser-tests/Tests/files/project-config-local-packages/cabal.project
new file mode 100644
index 00000000000..77ffb93ff00
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/files/project-config-local-packages/cabal.project
@@ -0,0 +1,70 @@
+program-options
+    ghc-options: -fno-state-hack -foo
+    gcc-options: -baz -quux
+
+program-locations
+    ghc-location: /tmp/bin/ghc
+    gcc-location: /tmp/bin/gcc
+
+extra-prog-path: /tmp/bin/extra, /usr/local/bin
+flags: +foo -bar
+library-vanilla: False
+shared: True
+static: True
+executable-dynamic: True
+executable-static: True
+profiling: True
+library-profiling: True
+profiling-shared: False
+executable-profiling: True
+profiling-detail: all-functions
+library-profiling-detail: exported-functions
+configure-options: -some-arg /some/path
+optimization: 2
+program-prefix: another/path
+program-suffix: and/another/path
+extra-lib-dirs: so, many, lib/dirs
+extra-lib-dirs-static: a/few, static/lib/dirs
+extra-framework-dirs: osx/framework, dirs
+extra-include-dirs: incredible/amount, of, include, directories
+library-for-ghci: False
+split-sections: True
+split-objs: True
+executable-stripping: False
+library-stripping: False
+tests: True
+benchmarks: True
+coverage: True
+relocatable: True
+debug-info: 3
+build-info: True
+run-tests: True
+documentation: True
+haddock-hoogle: True
+haddock-html: False
+haddock-html-location: http://hackage.haskell.org/packages/archive/$pkg/latest/doc/html
+haddock-foreign-libraries: True
+haddock-executables: True
+haddock-tests: True
+haddock-benchmarks: True
+haddock-internal: True
+haddock-css: some/path/to/file.css
+haddock-hyperlink-source: True
+haddock-quickjump: True
+haddock-hscolour-css: another/path/to/hscolour.css
+haddock-contents-location: https://example.com/$pkg/contents
+haddock-index-location: separately-generated/HTML/index
+haddock-base-url: https://example.com/haddock-base-url
+haddock-resources-dir: /haddock/static
+haddock-output-dir: /haddock/output
+haddock-use-unicode: False
+haddock-for-hackage: for-hackage
+
+test-log: human-log.log
+test-machine-log: machine.log
+test-keep-tix-files: True
+test-wrapper: /test-wrapper-path/
+test-fail-when-no-test-suites: True
+test-show-details: streaming
+test-options: --some-option 42
+benchmark-options: --some-benchmark-option --another-option
diff --git a/cabal-install/parser-tests/Tests/files/project-config-shared/cabal.project b/cabal-install/parser-tests/Tests/files/project-config-shared/cabal.project
new file mode 100644
index 00000000000..90f00f96278
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/files/project-config-shared/cabal.project
@@ -0,0 +1,39 @@
+builddir: something
+project-dir: my-project-dir
+project-file: my-project
+store-dir: a/store/dir/path
+per-component: True
+independent-goals: True
+ignore-project: False
+compiler: ghcjs
+with-compiler: /some/path/to/compiler
+with-hc-pkg: /some/path/to/ghc-pkg
+doc-index-file: /path/to/haddock-index
+package-dbs: clear, foo, clear, bar, baz
+active-repositories:
+  , hackage.haskell.org
+  , my-repository:override
+index-state:
+  , hackage.haskell.org 2020-05-06T22:33:27Z
+  , head.hackage 2020-04-29T04:11:05Z
+constraints: bar == 2.1,
+             bar +foo -baz
+preferences: foo == 0.9,
+             baz > 2.0
+cabal-lib-version: 1.24.0.1
+solver: modular
+allow-older: dep, pkga-1.1.2:dep-pkg
+allow-newer: pkgb-1.2.3:dep-pkgb, importantlib
+write-ghc-environment-files: always
+max-backjumps: 42
+reorder-goals: True
+count-conflicts: False
+fine-grained-conflicts: False
+minimize-conflict-set: True
+strong-flags: True
+allow-boot-library-installs: True
+reject-unconstrained-dependencies: all
+prefer-oldest: True
+extra-prog-path: /foo/bar, /baz/quux
+extra-prog-path-shared-only: /foo/bar, /baz/quux
+multi-repl: True
diff --git a/cabal-install/parser-tests/Tests/files/project-config-specific-packages/cabal.project b/cabal-install/parser-tests/Tests/files/project-config-specific-packages/cabal.project
new file mode 100644
index 00000000000..166b5db3d68
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/files/project-config-specific-packages/cabal.project
@@ -0,0 +1,12 @@
+package foo
+    profiling-detail: all-functions
+    library-profiling-detail: exported-functions
+    library-vanilla: True
+
+package bar
+    profiling-detail: late-toplevel
+    library-profiling-detail: none
+    program-prefix: prefix/path
+
+package baz
+    shared: True
diff --git a/cabal-install/parser-tests/Tests/files/relax-deps-concat/cabal.project b/cabal-install/parser-tests/Tests/files/relax-deps-concat/cabal.project
new file mode 100644
index 00000000000..8e328432b64
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/files/relax-deps-concat/cabal.project
@@ -0,0 +1,7 @@
+-- allow-newer: parallel-3.2.2.0:base
+allow-newer: cassava-0.5.2.0:base
+allow-newer: vector-th-unbox-0.2.1.7:base
+allow-newer: vector-th-unbox-0.2.1.7:template-haskell
+
+allow-older: mtl-2.3.1:base, aeson-2.2.3.0:bytestring
+allow-older: containers-0.7:array
diff --git a/cabal-install/parser-tests/Tests/files/remote-repos/cabal.project b/cabal-install/parser-tests/Tests/files/remote-repos/cabal.project
new file mode 100644
index 00000000000..819af437b03
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/files/remote-repos/cabal.project
@@ -0,0 +1,18 @@
+repository packages.example.org
+  url: http://packages.example.org/
+  secure: True
+  root-keys: 21, 42
+  key-threshold: 2
+
+repository more-packages.example.org
+  url: https://more-packages.example.org/
+  secure: True
+  root-keys: foo
+           , bar
+  key-threshold: 1
+
+repository my-secure-local-repository
+  url: file:/path/to/secure/repo
+  secure: True
+  root-keys: 123
+  key-threshold: 1
diff --git a/cabal-install/parser-tests/Tests/files/source-repository-packages/cabal.project b/cabal-install/parser-tests/Tests/files/source-repository-packages/cabal.project
new file mode 100644
index 00000000000..1ab7d417b54
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/files/source-repository-packages/cabal.project
@@ -0,0 +1,10 @@
+source-repository-package
+    type: git
+    location: https://example.com/Project.git
+    tag: 1234
+
+source-repository-package
+    type: git
+    location: https://example.com/example-dir/
+    tag: 12345
+    subdir: subproject
diff --git a/cabal-install/parser-tests/Tests/files/specific-packages-concat/cabal.project b/cabal-install/parser-tests/Tests/files/specific-packages-concat/cabal.project
new file mode 100644
index 00000000000..94766d451fa
--- /dev/null
+++ b/cabal-install/parser-tests/Tests/files/specific-packages-concat/cabal.project
@@ -0,0 +1,7 @@
+package foo
+    static: True
+    ghc-options: -fno-state-hack
+
+package foo
+    shared: True
+    ghc-options: -threaded
diff --git a/cabal-install/src/Distribution/Client/BuildReports/Anonymous.hs b/cabal-install/src/Distribution/Client/BuildReports/Anonymous.hs
index ce1d1665327..7bc6bb8872b 100644
--- a/cabal-install/src/Distribution/Client/BuildReports/Anonymous.hs
+++ b/cabal-install/src/Distribution/Client/BuildReports/Anonymous.hs
@@ -140,10 +140,10 @@ fieldDescrs =
 
 parseBuildReport :: BS.ByteString -> Either String BuildReport
 parseBuildReport s = case snd $ runParseResult $ parseFields s of
-  Left (_, perrors) -> Left $ unlines [err | PError _ err <- toList perrors]
+  Left (_, perrors) -> Left $ unlines [err | PErrorWithSource _ (PError _ err) <- toList perrors]
   Right report -> Right report
 
-parseFields :: BS.ByteString -> ParseResult BuildReport
+parseFields :: BS.ByteString -> ParseResult src BuildReport
 parseFields input = do
   fields <- either (parseFatalFailure zeroPos . show) pure $ readFields input
   case partitionFields fields of
diff --git a/cabal-install/src/Distribution/Client/Check.hs b/cabal-install/src/Distribution/Client/Check.hs
index eb053d7e46e..6ca20139855 100644
--- a/cabal-install/src/Distribution/Client/Check.hs
+++ b/cabal-install/src/Distribution/Client/Check.hs
@@ -16,19 +16,16 @@ import Distribution.Client.Compat.Prelude
 import Prelude ()
 
 import Distribution.Client.Errors
-import Distribution.Client.Utils.Parsec (renderParseError)
+
+import Distribution.Client.Errors.Parser
+import Distribution.Fields.ParseResult
 import Distribution.PackageDescription (GenericPackageDescription)
 import Distribution.PackageDescription.Check
 import Distribution.PackageDescription.Parsec
-  ( parseGenericPackageDescription
-  , runParseResult
-  )
-import Distribution.Parsec (PWarning (..), showPError)
+import Distribution.Parsec
 import Distribution.Simple.Utils (defaultPackageDescCwd, dieWithException, notice, warn, warnError)
 import Distribution.Utils.Path (getSymbolicPath)
 
-import System.IO (hPutStr, stderr)
-
 import qualified Control.Monad as CM
 import qualified Data.ByteString as BS
 import qualified Data.Function as F
@@ -36,19 +33,17 @@ import qualified Data.List as L
 import qualified Data.List.NonEmpty as NE
 import qualified System.Directory as Dir
 
-readGenericPackageDescriptionCheck :: Verbosity -> FilePath -> IO ([PWarning], GenericPackageDescription)
+readGenericPackageDescriptionCheck :: Verbosity -> FilePath -> IO ([PWarningWithSource CabalFileSource], GenericPackageDescription)
 readGenericPackageDescriptionCheck verbosity fpath = do
   exists <- Dir.doesFileExist fpath
   unless exists $
     dieWithException verbosity $
       FileDoesntExist fpath
   bs <- BS.readFile fpath
-  let (warnings, result) = runParseResult (parseGenericPackageDescription bs)
+  let (warnings, result) = runParseResult $ withSource (PCabalFile (fpath, bs)) (parseGenericPackageDescription bs)
   case result of
-    Left (_, errors) -> do
-      traverse_ (warn verbosity . showPError fpath) errors
-      hPutStr stderr $ renderParseError fpath bs errors warnings
-      dieWithException verbosity ParseError
+    Left (mspecVersion, errors) -> do
+      dieWithException verbosity (CabalCheckParseError (CabalFileParseError fpath bs errors mspecVersion warnings))
     Right x -> return (warnings, x)
 
 -- | Checks a package for common errors. Returns @True@ if the package
@@ -65,7 +60,7 @@ check verbosity ignores = do
   pdfile <- getSymbolicPath <$> defaultPackageDescCwd verbosity
   (ws, ppd) <- readGenericPackageDescriptionCheck verbosity pdfile
   -- convert parse warnings into PackageChecks
-  let ws' = map (wrapParseWarning pdfile) ws
+  let ws' = map (wrapParseWarning pdfile . pwarning) ws
   ioChecks <- checkPackageFilesGPD verbosity ppd "."
   let packageChecksPrim = ioChecks ++ checkPackage ppd ++ ws'
       (packageChecks, unrecs) = filterPackageChecksByIdString packageChecksPrim ignores
diff --git a/cabal-install/src/Distribution/Client/CmdConfigure.hs b/cabal-install/src/Distribution/Client/CmdConfigure.hs
index 8ce26f986ad..dbaec030520 100644
--- a/cabal-install/src/Distribution/Client/CmdConfigure.hs
+++ b/cabal-install/src/Distribution/Client/CmdConfigure.hs
@@ -159,7 +159,11 @@ configureAction' flags@NixStyleFlags{..} _extraArgs globalFlags = do
               (flagToMaybe . projectConfigHttpTransport $ projectConfigBuildOnly cliConfig)
           (CondNode conf imps bs) <-
             runRebuild (distProjectRootDirectory . distDirLayout $ baseCtx) $
-              readProjectLocalExtraConfig v httpTransport (distDirLayout baseCtx)
+              readProjectLocalExtraConfig
+                v
+                (fromFlagOrDefault defaultProjectFileParser $ projectConfigProjectFileParser $ projectConfigShared cliConfig)
+                httpTransport
+                (distDirLayout baseCtx)
           when (not (null imps && null bs)) $ dieWithException v UnableToPerformInplaceUpdate
           return (baseCtx, conf <> cliConfig)
         else return (baseCtx, cliConfig)
diff --git a/cabal-install/src/Distribution/Client/CmdInstall/ClientInstallFlags.hs b/cabal-install/src/Distribution/Client/CmdInstall/ClientInstallFlags.hs
index 1be09c514a9..32077fe7b99 100644
--- a/cabal-install/src/Distribution/Client/CmdInstall/ClientInstallFlags.hs
+++ b/cabal-install/src/Distribution/Client/CmdInstall/ClientInstallFlags.hs
@@ -1,4 +1,6 @@
+{-# LANGUAGE ConstraintKinds #-}
 {-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE PatternSynonyms #-}
 
 module Distribution.Client.CmdInstall.ClientInstallFlags
@@ -6,9 +8,12 @@ module Distribution.Client.CmdInstall.ClientInstallFlags
   , ClientInstallFlags (..)
   , defaultClientInstallFlags
   , clientInstallOptions
+  , clientInstallFlagsGrammar
   ) where
 
 import Distribution.Client.Compat.Prelude
+import Distribution.Compat.Lens (Lens')
+import Distribution.FieldGrammar
 import Prelude ()
 
 import Distribution.ReadE
@@ -35,6 +40,7 @@ import Distribution.Client.Types.InstallMethod
 import Distribution.Client.Types.OverwritePolicy
   ( OverwritePolicy (..)
   )
+import Distribution.Client.Utils.Parsec
 
 import qualified Distribution.Compat.CharParsing as P
 
@@ -114,6 +120,26 @@ clientInstallOptions _ =
       $ reqArg "DIR" (succeedReadE Flag) flagToList
   ]
 
+clientInstallFlagsGrammar
+  :: ( FieldGrammar c g
+     , Applicative (g ClientInstallFlags)
+     , c (Identity (Flag Bool))
+     , c (Flag' FilePathNT FilePath)
+     , c (Identity (Flag OverwritePolicy))
+     , c (Identity (Flag InstallMethod))
+     )
+  => g ClientInstallFlags ClientInstallFlags
+clientInstallFlagsGrammar =
+  ClientInstallFlags
+    <$> optionalFieldDef "lib" cinstInstallLibsLens mempty
+    <*> ( optionalFieldDefAla "package-env" (alaFlag FilePathNT) cinstEnvironmentPathLens mempty
+            <* optionalFieldDefAla "env" (alaFlag FilePathNT) cinstEnvironmentPathLens mempty
+        )
+    <*> optionalFieldDef "overwrite-policy" cinstOverwritePolicyLens mempty
+    <*> optionalFieldDef "install-method" cinstInstallMethodLens mempty
+    <*> optionalFieldDefAla "installdir" (alaFlag FilePathNT) cinstInstalldirLens mempty
+{-# SPECIALIZE clientInstallFlagsGrammar :: ParsecFieldGrammar' ClientInstallFlags #-}
+
 parsecInstallMethod :: CabalParsing m => m InstallMethod
 parsecInstallMethod = do
   name <- P.munch1 isAlpha
@@ -121,3 +147,23 @@ parsecInstallMethod = do
     "copy" -> pure InstallMethodCopy
     "symlink" -> pure InstallMethodSymlink
     _ -> P.unexpected $ "InstallMethod: " ++ name
+
+cinstInstallLibsLens :: Lens' ClientInstallFlags (Flag Bool)
+cinstInstallLibsLens f c = fmap (\x -> c{cinstInstallLibs = x}) (f (cinstInstallLibs c))
+{-# INLINEABLE cinstInstallLibsLens #-}
+
+cinstEnvironmentPathLens :: Lens' ClientInstallFlags (Flag FilePath)
+cinstEnvironmentPathLens f c = fmap (\x -> c{cinstEnvironmentPath = x}) (f (cinstEnvironmentPath c))
+{-# INLINEABLE cinstEnvironmentPathLens #-}
+
+cinstOverwritePolicyLens :: Lens' ClientInstallFlags (Flag OverwritePolicy)
+cinstOverwritePolicyLens f c = fmap (\x -> c{cinstOverwritePolicy = x}) (f (cinstOverwritePolicy c))
+{-# INLINEABLE cinstOverwritePolicyLens #-}
+
+cinstInstallMethodLens :: Lens' ClientInstallFlags (Flag InstallMethod)
+cinstInstallMethodLens f c = fmap (\x -> c{cinstInstallMethod = x}) (f (cinstInstallMethod c))
+{-# INLINEABLE cinstInstallMethodLens #-}
+
+cinstInstalldirLens :: Lens' ClientInstallFlags (Flag FilePath)
+cinstInstalldirLens f c = fmap (\x -> c{cinstInstalldir = x}) (f (cinstInstalldir c))
+{-# INLINEABLE cinstInstalldirLens #-}
diff --git a/cabal-install/src/Distribution/Client/Config.hs b/cabal-install/src/Distribution/Client/Config.hs
index 77348dbc638..d0c3db2c32e 100644
--- a/cabal-install/src/Distribution/Client/Config.hs
+++ b/cabal-install/src/Distribution/Client/Config.hs
@@ -675,6 +675,7 @@ instance Semigroup SavedConfig where
           { flagProjectDir = combine flagProjectDir
           , flagProjectFile = combine flagProjectFile
           , flagIgnoreProject = combine flagIgnoreProject
+          , flagProjectFileParser = combine flagProjectFileParser
           }
         where
           combine = combine' savedProjectFlags
diff --git a/cabal-install/src/Distribution/Client/Errors.hs b/cabal-install/src/Distribution/Client/Errors.hs
index 06f965fd972..4270435b54f 100644
--- a/cabal-install/src/Distribution/Client/Errors.hs
+++ b/cabal-install/src/Distribution/Client/Errors.hs
@@ -37,6 +37,8 @@ import Text.PrettyPrint hiding (render, (<>))
 import qualified Text.PrettyPrint as PP
 import Text.Regex.Posix.ByteString (WrapError)
 
+import Distribution.Client.Errors.Parser
+
 data CabalInstallException
   = UnpackGet
   | NotTarballDir FilePath
@@ -61,7 +63,7 @@ data CabalInstallException
   | UnableToPerformInplaceUpdate
   | EmptyValuePagerEnvVariable
   | FileDoesntExist FilePath
-  | ParseError
+  | CabalCheckParseError CabalFileParseError
   | CabalFileNotFound FilePath
   | FindOpenProgramLocationErr String
   | PkgConfParseFailed String
@@ -187,6 +189,9 @@ data CabalInstallException
   | CmdPathAcceptsNoTargets
   | CmdPathCommandDoesn'tSupportDryRun
   | GenBoundsDoesNotSupportScript FilePath
+  | LegacyAndParsecParseResultsDiffer FilePath String String
+  | CabalFileParseFailure CabalFileParseError
+  | ProjectConfigParseFailure ProjectConfigParseError
   deriving (Show)
 
 exceptionCodeCabalInstall :: CabalInstallException -> Int
@@ -214,7 +219,7 @@ exceptionCodeCabalInstall e = case e of
   UnableToPerformInplaceUpdate{} -> 7032
   EmptyValuePagerEnvVariable{} -> 7033
   FileDoesntExist{} -> 7034
-  ParseError{} -> 7035
+  CabalCheckParseError{} -> 7035
   CabalFileNotFound{} -> 7036
   FindOpenProgramLocationErr{} -> 7037
   PkgConfParseFailed{} -> 7038
@@ -340,6 +345,9 @@ exceptionCodeCabalInstall e = case e of
   CmdPathAcceptsNoTargets{} -> 7161
   CmdPathCommandDoesn'tSupportDryRun -> 7163
   GenBoundsDoesNotSupportScript{} -> 7164
+  LegacyAndParsecParseResultsDiffer{} -> 7165
+  CabalFileParseFailure{} -> 7166
+  ProjectConfigParseFailure{} -> 7167
 
 exceptionMessageCabalInstall :: CabalInstallException -> String
 exceptionMessageCabalInstall e = case e of
@@ -378,7 +386,7 @@ exceptionMessageCabalInstall e = case e of
   UnableToPerformInplaceUpdate -> "local project file has conditional and/or import logic, unable to perform and automatic in-place update"
   EmptyValuePagerEnvVariable -> "man: empty value of the PAGER environment variable"
   FileDoesntExist fpath -> "Error Parsing: file \"" ++ fpath ++ "\" doesn't exist. Cannot continue."
-  ParseError -> "parse error"
+  CabalCheckParseError err -> renderCabalFileParseError err
   CabalFileNotFound cabalFile -> "Package .cabal file not found in the tarball: " ++ cabalFile
   FindOpenProgramLocationErr err -> err
   PkgConfParseFailed perror ->
@@ -864,6 +872,19 @@ exceptionMessageCabalInstall e = case e of
     "The 'path' command doesn't support the flag '--dry-run'."
   GenBoundsDoesNotSupportScript{} ->
     "The 'gen-bounds' command does not support script targets."
+  LegacyAndParsecParseResultsDiffer _fp legacyParsec parsec ->
+    unlines
+      [ "The legacy and parsec parsers produced different results for the project file. This is unexpected, please report this as a bug."
+      , "The legacy parser will be removed in the next major version."
+      , "Legacy parse result:"
+      , legacyParsec
+      , "Parsec parse result:"
+      , parsec
+      ]
+  CabalFileParseFailure cbfError ->
+    renderCabalFileParseError cbfError
+  ProjectConfigParseFailure pcfError ->
+    renderProjectConfigParseError pcfError
 
 instance Exception (VerboseException CabalInstallException) where
   displayException :: VerboseException CabalInstallException -> [Char]
diff --git a/cabal-install/src/Distribution/Client/Errors/Parser.hs b/cabal-install/src/Distribution/Client/Errors/Parser.hs
new file mode 100644
index 00000000000..9b917db9886
--- /dev/null
+++ b/cabal-install/src/Distribution/Client/Errors/Parser.hs
@@ -0,0 +1,294 @@
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+
+module Distribution.Client.Errors.Parser where
+
+import Distribution.Client.Compat.Prelude
+import System.FilePath (normalise)
+import Prelude ()
+
+import qualified Data.ByteString.Char8 as BS8
+import qualified Data.List.NonEmpty as NE
+import qualified Data.Map as Map
+import qualified Data.Map.Merge.Strict as Map
+import Distribution.Parsec
+import Distribution.Parsec.Source
+import Distribution.Simple.Utils (fromUTF8BS)
+import Distribution.Solver.Types.ProjectConfigPath
+import Distribution.Version (Version)
+import Text.PrettyPrint (render)
+
+-- Error when parsing a .cabal file
+
+-- | Errors reported upon failing to parse a @.cabal@ file.
+data CabalFileParseError
+  = CabalFileParseError
+      FilePath
+      -- ^ @.cabal@ file path
+      BS8.ByteString
+      -- ^ @.cabal@ file contents
+      (NonEmpty (PErrorWithSource CabalFileSource))
+      -- ^ errors
+      (Maybe Version)
+      -- ^ We might discover the spec version the package needs
+      [PWarningWithSource CabalFileSource]
+      -- ^ warnings
+
+-- | Manual instance which skips file contents
+instance Show CabalFileParseError where
+  showsPrec d (CabalFileParseError fp _ es mv ws) =
+    showParen (d > 10) $
+      showString "CabalFileParseError"
+        . showChar ' '
+        . showsPrec 11 fp
+        . showChar ' '
+        . showsPrec 11 ("" :: String)
+        . showChar ' '
+        . showsPrec 11 es
+        . showChar ' '
+        . showsPrec 11 mv
+        . showChar ' '
+        . showsPrec 11 ws
+
+instance Exception CabalFileParseError where
+  displayException = renderCabalFileParseError
+
+renderCabalFileParseError :: CabalFileParseError -> String
+renderCabalFileParseError (CabalFileParseError _filePath _contents errors _ warnings) =
+  renderParseErrorCabalFile errors warnings
+
+-- Error when parsing a project file
+
+-- | Errors reported upon failing to parse a @cabal.project@ file.
+data ProjectConfigParseError
+  = ProjectConfigParseError
+      (NonEmpty (PErrorWithSource ProjectFileSource))
+      -- ^ errors
+      [PWarningWithSource ProjectFileSource]
+      -- ^ warnings
+
+-- | Manual instance which skips file contents
+instance Show ProjectConfigParseError where
+  showsPrec d (ProjectConfigParseError es ws) =
+    showParen (d > 10) $
+      showString "ProjectConfigParseError"
+        . showChar ' '
+        . showsPrec 11 es
+        . showChar ' '
+        . showsPrec 11 ws
+
+instance Exception ProjectConfigParseError where
+  displayException = renderProjectConfigParseError
+
+renderProjectConfigParseError :: ProjectConfigParseError -> String
+renderProjectConfigParseError (ProjectConfigParseError errors warnings) =
+  renderParseError displayProjectFileSource errors warnings
+  where
+    displayProjectFileSource (ProjectFileSource (path, contents)) =
+      renderParseErrorFile "project" (currentProjectConfigPath path) (if isTopLevelConfigPath path then Nothing else Just $ render (docProjectImportedBy path)) contents
+
+data ProjectFileSource = ProjectFileSource (ProjectConfigPath, BS8.ByteString) deriving (Show, Generic)
+
+instance Eq ProjectFileSource where
+  (ProjectFileSource (path1, _)) == (ProjectFileSource (path2, _)) = path1 == path2
+
+instance Ord ProjectFileSource where
+  (ProjectFileSource (path1, _)) `compare` (ProjectFileSource (path2, _)) = path1 `compare` path2
+
+renderProjectFileSource :: ProjectFileSource -> String
+renderProjectFileSource (ProjectFileSource (path, _contents)) =
+  currentProjectConfigPath path
+
+renderParseErrorCabalFile :: NonEmpty (PErrorWithSource CabalFileSource) -> [PWarningWithSource CabalFileSource] -> String
+renderParseErrorCabalFile errors warnings =
+  renderParseError renderCabalFileSourceMsgs errors warnings
+
+-- | Render parse error highlighting the part of the input file.
+renderParseError
+  :: forall src
+   . (Ord src, Eq src)
+  => (src -> ([PError], [PWarning]) -> String)
+  -> NonEmpty (PErrorWithSource src)
+  -> [PWarningWithSource src]
+  -> String
+renderParseError display errors warnings =
+  unlines [renderParseErrorsWarnings (fmap display source) ws | (source, ws) <- joinedErrorsWarningsList]
+  where
+    mkErrorGroup :: NonEmpty (PErrorWithSource src) -> (PSource src, [PError])
+    mkErrorGroup (x :| xs) = (perrorSource x, perror x : map perror xs)
+
+    mkWarningGroup :: NonEmpty (PWarningWithSource src) -> (PSource src, [PWarning])
+    mkWarningGroup (x :| xs) = (pwarningSource x, pwarning x : map pwarning xs)
+
+    groupedErrors =
+      Map.fromListWith (++) $
+        map mkErrorGroup $
+          NE.groupBy
+            (\a b -> perrorSource a == perrorSource b)
+            errors
+    groupedWarnings =
+      Map.fromListWith (++) $
+        map mkWarningGroup $
+          NE.groupBy
+            (\a b -> pwarningSource a == pwarningSource b)
+            warnings
+
+    joinedErrorsWarnings :: Map.Map (PSource src) ([PError], [PWarning])
+    joinedErrorsWarnings = Map.merge (Map.mapMissing (\_ es -> (es, []))) (Map.mapMissing (\_ ps -> ([], ps))) (Map.zipWithMatched (\_ es ps -> (es, ps))) groupedErrors groupedWarnings
+
+    joinedErrorsWarningsList = Map.toList joinedErrorsWarnings
+
+renderParseErrorsWarnings :: PSource (([PError], [PWarning]) -> String) -> ([PError], [PWarning]) -> String
+renderParseErrorsWarnings source (errors, warnings) =
+  case source of
+    PKnownSource src -> src (errors, warnings)
+    PUnknownSource -> renderParseErrorNoFile "" errors warnings
+
+renderCabalFileSourceMsgs :: CabalFileSource -> ([PError], [PWarning]) -> String
+renderCabalFileSourceMsgs (PCabalFile (fpath, contents)) (errors, warnings) =
+  renderParseErrorFile "cabal" fpath Nothing contents (errors, warnings)
+
+renderInstalledPackageInfoSourceMsgs :: InstalledPackageInfoSource -> ([PError], [PWarning]) -> String
+renderInstalledPackageInfoSourceMsgs PInstalledPackageInfo (errors, warnings) =
+  renderParseErrorNoFile "installed package info" errors warnings
+
+renderParseErrorNoFile :: String -> [PError] -> [PWarning] -> String
+renderParseErrorNoFile herald errors warnings =
+  renderParseErrorGeneral herald Nothing Nothing (const []) errors warnings
+
+-- | Render a parse error which resulted from a file on disk
+renderParseErrorFile
+  :: String
+  -- ^ Human name for the kind of file (i.e. cabal, project "file")
+  -> FilePath
+  -- ^ Path to the file
+  -> Maybe String
+  -- ^ Provenance, any additional contextual info to print
+  -> BS8.ByteString
+  -- ^ Contents of the file
+  -> ([PError], [PWarning])
+  -> String
+renderParseErrorFile herald filepath provenance contents (errors, warnings) =
+  renderParseErrorGeneral (herald <> " file " <> filepath) (Just (filepath' <> ":")) provenance formatInput errors warnings
+  where
+    filepath' = normalise filepath
+
+    -- lines of the input file. 'lines' is taken, so they are called rows
+    -- contents, line number, whether it's empty line
+    rows :: [(String, Int, Bool)]
+    rows = zipWith f (BS8.lines contents) [1 ..]
+      where
+        f bs i = let s = fromUTF8BS bs in (s, i, isEmptyOrComment s)
+
+    rowsZipper = listToZipper rows
+
+    isEmptyOrComment :: String -> Bool
+    isEmptyOrComment s = case dropWhile (== ' ') s of
+      "" -> True -- empty
+      ('-' : '-' : _) -> True -- comment
+      _ -> False
+
+    -- format line: prepend the given line number
+    formatInput :: Position -> [String]
+    formatInput (Position row col) = case advance (row - 1) rowsZipper of
+      Zipper xs ys -> before ++ after
+        where
+          before = case span (\(_, _, b) -> b) xs of
+            (_, []) -> []
+            (zs, z : _) -> map formatInputLine $ z : reverse zs
+
+          after = case ys of
+            [] -> []
+            (z : _zs) ->
+              [ formatInputLine z -- error line
+              , "      | " ++ replicate (col - 1) ' ' ++ "^" -- pointer: ^
+              ]
+    -- do we need rows after?
+    -- ++ map formatInputLine (take 1 zs)           -- one row after
+
+    formatInputLine :: (String, Int, Bool) -> String
+    formatInputLine (str, row, _) = leftPadShow row ++ " | " ++ str
+
+    -- hopefully we don't need to work with over 99999 lines .cabal files
+    -- at that point small glitches in error messages are hopefully fine.
+    leftPadShow :: Int -> String
+    leftPadShow n = let s = show n in replicate (5 - length s) ' ' ++ s
+
+-- | A generic rendering function which can render from many sources.
+renderParseErrorGeneral
+  :: String
+  -- ^ What we were parsing when the error occurred.
+  -> Maybe String
+  -- ^ A simpler/shorter header to display when displaying each error (normally a filepath)
+  -> Maybe String
+  -- ^ Provenance, used to print additional context about what file failed (used to print the import path of a project
+  -- file which failed to parse)
+  -> (Position -> [String])
+  -- ^ Extra information to render based on the position
+  -> [PError]
+  -> [PWarning]
+  -> String
+renderParseErrorGeneral header err_header provenance extra_info errors warnings =
+  unlines $
+    [ warningsOrErrors <> " parsing" <> header' <> ":"
+    ]
+      ++ [p | Just p <- [provenance]]
+      ++ [""] -- Place a newline between the header and the errors/warnings
+      -- Place a newline between each error and warning
+      ++ intersperse "" (renderedWarnings ++ renderedErrors)
+  where
+    warningsOrErrors = case errors of
+      [] -> case warnings of
+        [_] -> "Warning"
+        _ -> "Warnings"
+      [_] -> "Error"
+      _ -> "Errors"
+
+    header' = if null header then "" else (" " <> header)
+
+    renderedErrors = map renderError (sortBy (comparing perrorPosition) errors)
+    renderedWarnings = map renderWarning (sortBy (comparing pwarningPosition) warnings)
+
+    renderErrorOrWarning :: String -> Position -> String -> String
+    renderErrorOrWarning err_type pos msg
+      -- if position is 0:0, then it doesn't make sense to show input
+      -- looks like, Parsec errors have line-feed in them
+      | pos == zeroPos = unlines (herald : map indent user_msg)
+      | otherwise = unlines (herald : map indent (user_msg ++ extra_info pos))
+      where
+        herald = renderErrorHerald pos ++ err_type ++ ":"
+        user_msg = lines (trimLF msg)
+
+    indent :: String -> String
+    indent s = replicate 2 ' ' ++ s
+
+    -- Don't render the 0:0 position
+    renderErrorHerald :: Position -> String
+    renderErrorHerald pos =
+      case (err_header, pos == zeroPos) of
+        (Nothing, True) -> ""
+        (Nothing, False) -> showPos pos ++ ": "
+        (Just herald, True) -> herald ++ " "
+        (Just herald, False) -> herald ++ showPos pos ++ ": "
+
+    renderError :: PError -> String
+    renderError (PError pos msg) = renderErrorOrWarning "error" pos msg
+
+    renderWarning :: PWarning -> String
+    renderWarning (PWarning _ pos msg) = renderErrorOrWarning "warning" pos msg
+
+    -- sometimes there are (especially trailing) newlines.
+    trimLF :: String -> String
+    trimLF = dropWhile (== '\n') . reverse . dropWhile (== '\n') . reverse
+
+data Zipper a = Zipper [a] [a]
+
+listToZipper :: [a] -> Zipper a
+listToZipper = Zipper []
+
+advance :: Int -> Zipper a -> Zipper a
+advance n z@(Zipper xs ys)
+  | n <= 0 = z
+  | otherwise = case ys of
+      [] -> z
+      (y : ys') -> advance (n - 1) $ Zipper (y : xs) ys'
diff --git a/cabal-install/src/Distribution/Client/ParseUtils.hs b/cabal-install/src/Distribution/Client/ParseUtils.hs
index 5d4bd8331a1..54d4c622976 100644
--- a/cabal-install/src/Distribution/Client/ParseUtils.hs
+++ b/cabal-install/src/Distribution/Client/ParseUtils.hs
@@ -89,9 +89,9 @@ import Distribution.FieldGrammar (parseFieldGrammar, partitionFields)
 import qualified Distribution.FieldGrammar as FG
 import qualified Distribution.Fields as F
 import Distribution.Fields.ParseResult (runParseResult)
-import Distribution.Parsec.Error (showPError)
+import Distribution.Parsec.Error (showPErrorWithSource)
 import Distribution.Parsec.Position (Position (..))
-import Distribution.Parsec.Warning (showPWarning)
+import Distribution.Parsec.Warning (showPWarningWithSource)
 import Distribution.Simple.Utils (fromUTF8BS, toUTF8BS)
 
 -------------------------
@@ -321,12 +321,12 @@ parseFieldsAndSections fieldDescrs sectionDescrs fgSectionDescrs =
                 ++ show line'
           case runParseResult $ parseFieldGrammar cabalSpecLatest fields2 grammar of
             (warnings, Right b) -> do
-              for_ warnings $ \w -> warning $ showPWarning "???" w
+              for_ warnings $ \w -> warning $ showPWarningWithSource $ w
               setter line param b a
             (warnings, Left (_, errs)) -> do
-              for_ warnings $ \w -> warning $ showPWarning "???" w
+              for_ warnings $ \w -> warning $ showPWarningWithSource $ w
               case errs of
-                err :| _errs -> fail $ showPError "???" err
+                err :| _errs -> fail $ showPErrorWithSource $ err
         Nothing -> do
           warning $
             "Unrecognized section '"
diff --git a/cabal-install/src/Distribution/Client/ProjectConfig.hs b/cabal-install/src/Distribution/Client/ProjectConfig.hs
index 5d2c3981c0e..32d8048b2b5 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig.hs
@@ -1,8 +1,10 @@
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE NamedFieldPuns #-}
 {-# LANGUAGE PatternSynonyms #-}
 {-# LANGUAGE RecordWildCards #-}
 {-# LANGUAGE TypeApplications #-}
+{-# OPTIONS_GHC -Wno-unused-matches #-}
 
 -- | Handling project configuration.
 module Distribution.Client.ProjectConfig
@@ -11,6 +13,7 @@ module Distribution.Client.ProjectConfig
   , ProjectConfigToParse (..)
   , ProjectConfigBuildOnly (..)
   , ProjectConfigShared (..)
+  , ProjectConfigSkeleton
   , ProjectConfigProvenance (..)
   , PackageConfig (..)
   , MapLast (..)
@@ -40,6 +43,12 @@ module Distribution.Client.ProjectConfig
   , readSourcePackageCabalFile
   , readSourcePackageCabalFile'
   , CabalFileParseError (..)
+  , readProjectFileSkeleton
+  , ProjectFileParser (..)
+  , readProjectFileSkeletonLegacy
+  , readProjectFileSkeletonParsec
+  , readProjectFileSkeletonFallback
+  , readProjectFileSkeletonCompare
 
     -- * Packages within projects
   , ProjectPackageLocation (..)
@@ -68,8 +77,10 @@ module Distribution.Client.ProjectConfig
   ) where
 
 import Distribution.Client.Compat.Prelude hiding (empty)
+import Distribution.Parsec.Source
 import Distribution.Simple.Utils
   ( createDirectoryIfMissingVerbose
+  , debug
   , dieWithException
   , maybeExit
   , notice
@@ -86,6 +97,7 @@ import Distribution.Client.Glob
   )
 import Distribution.Client.JobControl
 import Distribution.Client.ProjectConfig.Legacy
+import qualified Distribution.Client.ProjectConfig.Parsec as Parsec
 import Distribution.Client.ProjectConfig.Types
 import Distribution.Client.RebuildMonad
 import Distribution.Client.VCS
@@ -96,6 +108,7 @@ import Distribution.Client.VCS
   , syncSourceRepos
   , validateSourceRepos
   )
+import Distribution.Fields.ParseResult
 
 import Distribution.Client.BuildReports.Types
   ( ReportLevel (..)
@@ -110,6 +123,7 @@ import Distribution.Client.DistDirLayout
   , ProjectRoot (..)
   , defaultProjectFile
   )
+import Distribution.Client.Errors.Parser
 import Distribution.Client.GlobalFlags
   ( RepoContext (..)
   , withRepoContext'
@@ -122,7 +136,6 @@ import Distribution.Client.HttpUtils
   , transportCheckHttps
   )
 import Distribution.Client.Types
-import Distribution.Client.Utils.Parsec (renderParseError)
 
 import Distribution.Solver.Types.ConstraintSource
 import Distribution.Solver.Types.PackageConstraint
@@ -154,11 +167,6 @@ import qualified Distribution.Deprecated.ProjectParseUtils as OldParser
   ( ProjectParseResult (..)
   )
 import Distribution.Fields
-  ( PError
-  , PWarning
-  , runParseResult
-  , showPWarning
-  )
 import Distribution.Package
 import Distribution.PackageDescription.Parsec
   ( parseGenericPackageDescription
@@ -751,35 +759,37 @@ withProjectOrGlobalConfig' with without = do
 -- file if any, plus other global config.
 readProjectConfig
   :: Verbosity
+  -> ProjectFileParser
   -> HttpTransport
   -> Flag Bool
   -- ^ @--ignore-project@
   -> Flag FilePath
   -> DistDirLayout
   -> Rebuild ProjectConfigSkeleton
-readProjectConfig verbosity _ (Flag True) configFileFlag _ = do
+readProjectConfig verbosity parserOption _ (Flag True) configFileFlag _ = do
   global <- singletonProjectConfigSkeleton <$> readGlobalConfig verbosity configFileFlag
   return (global <> singletonProjectConfigSkeleton defaultImplicitProjectConfig)
-readProjectConfig verbosity httpTransport _ configFileFlag distDirLayout = do
+readProjectConfig verbosity parserOption httpTransport _ configFileFlag distDirLayout = do
   global <- singletonProjectConfigSkeleton <$> readGlobalConfig verbosity configFileFlag
-  local <- readProjectLocalConfigOrDefault verbosity httpTransport distDirLayout
-  freeze <- readProjectLocalFreezeConfig verbosity httpTransport distDirLayout
-  extra <- readProjectLocalExtraConfig verbosity httpTransport distDirLayout
+  local <- readProjectLocalConfigOrDefault verbosity parserOption httpTransport distDirLayout
+  freeze <- readProjectLocalFreezeConfig verbosity parserOption httpTransport distDirLayout
+  extra <- readProjectLocalExtraConfig verbosity parserOption httpTransport distDirLayout
   return (global <> local <> freeze <> extra)
 
 -- | Reads an explicit @cabal.project@ file in the given project root dir,
 -- or returns the default project config for an implicitly defined project.
 readProjectLocalConfigOrDefault
   :: Verbosity
+  -> ProjectFileParser
   -> HttpTransport
   -> DistDirLayout
   -> Rebuild ProjectConfigSkeleton
-readProjectLocalConfigOrDefault verbosity httpTransport distDirLayout = do
+readProjectLocalConfigOrDefault verbosity parserOption httpTransport distDirLayout = do
   let projectFile = distProjectFile distDirLayout ""
   usesExplicitProjectRoot <- liftIO $ doesFileExist projectFile
   if usesExplicitProjectRoot
     then do
-      readProjectFileSkeleton verbosity httpTransport distDirLayout "" "project file"
+      readProjectFileSkeleton parserOption verbosity httpTransport distDirLayout "" "project file"
     else do
       monitorFiles [monitorNonExistentFile projectFile]
       return (singletonProjectConfigSkeleton defaultImplicitProjectConfig)
@@ -797,11 +807,13 @@ defaultImplicitProjectConfig =
 -- principle can be edited manually or by other tools.
 readProjectLocalExtraConfig
   :: Verbosity
+  -> ProjectFileParser
   -> HttpTransport
   -> DistDirLayout
   -> Rebuild ProjectConfigSkeleton
-readProjectLocalExtraConfig verbosity httpTransport distDirLayout =
+readProjectLocalExtraConfig verbosity parserOption httpTransport distDirLayout =
   readProjectFileSkeleton
+    parserOption
     verbosity
     httpTransport
     distDirLayout
@@ -813,11 +825,13 @@ readProjectLocalExtraConfig verbosity httpTransport distDirLayout =
 -- principle can be edited manually or by other tools.
 readProjectLocalFreezeConfig
   :: Verbosity
+  -> ProjectFileParser
   -> HttpTransport
   -> DistDirLayout
   -> Rebuild ProjectConfigSkeleton
-readProjectLocalFreezeConfig verbosity httpTransport distDirLayout =
+readProjectLocalFreezeConfig verbosity parserOption httpTransport distDirLayout =
   readProjectFileSkeleton
+    parserOption
     verbosity
     httpTransport
     distDirLayout
@@ -825,30 +839,148 @@ readProjectLocalFreezeConfig verbosity httpTransport distDirLayout =
     "project freeze file"
 
 -- | Reads a named extended (with imports and conditionals) config file in the given project root dir, or returns empty.
-readProjectFileSkeleton :: Verbosity -> HttpTransport -> DistDirLayout -> String -> String -> Rebuild ProjectConfigSkeleton
-readProjectFileSkeleton
+-- This function is generic and can be used with the legacy or parsec parser, or a combination of both.
+readProjectFileSkeletonGen :: Verbosity -> HttpTransport -> DistDirLayout -> String -> String -> (FilePath -> IO ProjectConfigSkeleton) -> Rebuild ProjectConfigSkeleton
+readProjectFileSkeletonGen
   verbosity
   httpTransport
-  DistDirLayout{distProjectFile, distDownloadSrcDirectory}
+  dir
   extensionName
-  extensionDescription = do
-    exists <- liftIO $ doesFileExist extensionFile
-    if exists
-      then do
-        monitorFiles [monitorFileHashed extensionFile]
-        pcs <- liftIO readExtensionFile
-        monitorFiles $ map monitorFileHashed (projectConfigPathRoot <$> projectSkeletonImports pcs)
-        pure pcs
-      else do
-        monitorFiles [monitorNonExistentFile extensionFile]
-        return mempty
+  extensionDescription
+  parseConfig =
+    do
+      exists <- liftIO $ doesFileExist extensionFile
+      if exists
+        then do
+          monitorFiles [monitorFileHashed extensionFile]
+          pcs <- liftIO $ parseConfig extensionFile
+          monitorFiles $ map monitorFileHashed (projectConfigPathRoot <$> projectSkeletonImports pcs)
+          return pcs
+        else do
+          monitorFiles [monitorNonExistentFile extensionFile]
+          return mempty
     where
-      extensionFile = distProjectFile extensionName
+      extensionFile = (distProjectFile dir) extensionName
+
+-- There are 3 different variants of the project parsing function.
+-- 1. readProjectFileSkeletonLegacy: always uses the legacy parser
+-- 2. readProjectFileSkeletonParsec: always uses the parsec parser
+-- 3. readProjectFileSkeletonFallback: uses the parsec parser, but if that fails, it falls back to the legacy parser.
+-- 4. readProjectFileSkeletonCompare: Run both parsers, and compare the results to check they are the same.
+--
+--
+-- correspondingly there are two "pure" functions to attempt to parse a project
+-- file using the "legacy" or "parsec" parser.
+--
+-- 1. parseProjectFileSkeletonLegacy: parses a project file using the legacy parser
+-- 2. parseProjectFileSkeletonParsec: parses a project file using the parsec parser
+--
+-- Errors are handled in each case by
+--
+-- 1. reportParseResult: reports legacy parse errors to the user
+-- 2. reportParseResultParsec: reports parsec parse errors to the user
+
+readProjectFileSkeleton :: ProjectFileParser -> Verbosity -> HttpTransport -> DistDirLayout -> String -> String -> Rebuild ProjectConfigSkeleton
+readProjectFileSkeleton option =
+  case option of
+    LegacyParser -> readProjectFileSkeletonLegacy
+    ParsecParser -> readProjectFileSkeletonParsec
+    FallbackParser -> readProjectFileSkeletonFallback
+    CompareParser -> readProjectFileSkeletonCompare
+
+-- | Read a project file using the legacy parser.
+readProjectFileSkeletonLegacy :: Verbosity -> HttpTransport -> DistDirLayout -> String -> String -> Rebuild ProjectConfigSkeleton
+readProjectFileSkeletonLegacy verbosity httpTransport distDirLayout extensionName extensionDescription = do
+  readProjectFileSkeletonGen verbosity httpTransport distDirLayout extensionName extensionDescription $ \fp -> do
+    debug verbosity $ "Reading project file using the legacy parser"
+    parseProjectFileSkeletonLegacy verbosity httpTransport distDirLayout extensionName extensionDescription fp
+      >>= liftIO . reportParseResult verbosity extensionDescription fp
+
+-- | Read a project file using the parsec parser, but if that fails, it falls back to the legacy parser.
+readProjectFileSkeletonFallback :: Verbosity -> HttpTransport -> DistDirLayout -> String -> String -> Rebuild ProjectConfigSkeleton
+readProjectFileSkeletonFallback verbosity httpTransport distDirLayout extensionName extensionDescription = do
+  readProjectFileSkeletonGen verbosity httpTransport distDirLayout extensionName extensionDescription $ \fp -> do
+    debug verbosity $ "Reading project file using the fallback parser"
+    (res, bs) <- parseProjectFileSkeletonParsec verbosity httpTransport distDirLayout extensionName extensionDescription fp
+    let (_, pres) = runParseResult res
+    case pres of
+      -- 1. Successful parse with parsec parser, handle the result as normal.
+      Right{} -> liftIO $ reportParseResultParsec verbosity fp bs res
+      -- 2. The parse failed with the parsec parser, fallback to the legacy parser.
+      Left{} -> do
+        lres <- parseProjectFileSkeletonLegacy verbosity httpTransport distDirLayout extensionName extensionDescription fp
+        case lres of
+          -- 3a. The legacy parser worked, but the parsec parser failed!
+          -- Report a warning to the user that this happened.
+          OldParser.ProjectParseOk{} -> do
+            warn verbosity $ "The new parsec parser failed, but the legacy parser worked. This is unexpected, please report this as a bug.\nThe legacy parser will be removed in the next major version."
+            liftIO $ reportParseResult verbosity extensionDescription fp lres
+          -- 3b. The legacy parser failed as well, report the original error.
+          OldParser.ProjectParseFailed{} -> do
+            liftIO $ reportParseResultParsec verbosity fp bs res
+
+-- | Read a project file using the parsec parser.
+readProjectFileSkeletonParsec :: Verbosity -> HttpTransport -> DistDirLayout -> String -> String -> Rebuild ProjectConfigSkeleton
+readProjectFileSkeletonParsec verbosity httpTransport distDirLayout extensionName extensionDescription = do
+  readProjectFileSkeletonGen verbosity httpTransport distDirLayout extensionName extensionDescription $ \fp -> do
+    debug verbosity $ "Reading project file using the parsec parser"
+    (res, bs) <- parseProjectFileSkeletonParsec verbosity httpTransport distDirLayout extensionName extensionDescription fp
+    liftIO $ reportParseResultParsec verbosity fp bs res
+
+readProjectFileSkeletonCompare :: Verbosity -> HttpTransport -> DistDirLayout -> String -> String -> Rebuild ProjectConfigSkeleton
+readProjectFileSkeletonCompare verbosity httpTransport distDirLayout extensionName extensionDescription = do
+  readProjectFileSkeletonGen verbosity httpTransport distDirLayout extensionName extensionDescription $ \fp -> do
+    debug verbosity $ "Reading project file using the comparative parser"
+    (pres, bs) <- parseProjectFileSkeletonParsec verbosity httpTransport distDirLayout extensionName extensionDescription fp
+    lres <- parseProjectFileSkeletonLegacy verbosity httpTransport distDirLayout extensionName extensionDescription fp
+    let (_, ppres) = runParseResult pres
+    case (lres, ppres) of
+      -- 1. Both succeed, compare the results
+      (OldParser.ProjectParseOk lwarns lpcs, Right ppcs) -> do
+        unless (lpcs == ppcs) (dieWithException verbosity $ LegacyAndParsecParseResultsDiffer fp (show lpcs) (show ppcs))
+        liftIO $ reportParseResultParsec verbosity fp bs pres
+      -- 2. The legacy parser failed, but the parsec parser succeeded.
+      -- Report a warning to the user that this happened.
+      (OldParser.ProjectParseFailed{}, Right{}) -> do
+        warn verbosity $ "The legacy parser failed, but the new parsec parser worked. This is unexpected, please report this as a bug.\nThe legacy parser will be removed in the next major version."
+        liftIO $ reportParseResult verbosity extensionDescription fp lres
+      -- 3. The legacy parser succeeded, but the parsec parser failed.
+      -- Report a warning to the user that this happened.
+      (OldParser.ProjectParseOk{}, Left{}) -> do
+        warn verbosity $ "The new parsec parser failed, but the legacy parser worked. This is unexpected, please report this as a bug.\nThe legacy parser will be removed in the next major version."
+        liftIO $ reportParseResult verbosity extensionDescription fp lres
+      (OldParser.ProjectParseFailed{}, Left{}) -> do
+        -- 4. Both failed, report the original error. We don't check that the same errors are reported.
+        liftIO $ reportParseResultParsec verbosity fp bs pres
+
+reportParseResultParsec
+  :: Verbosity
+  -> FilePath
+  -> BS.ByteString
+  -> Parsec.ParseResult ProjectFileSource a
+  -> IO a
+reportParseResultParsec verbosity fpath contents pr = do
+  let (warnings, result) = runParseResult pr
+  case result of
+    Right x -> do
+      let sortKey p = (pwarningSource p, pwarningPosition (pwarning p))
+          sortedWarnings = sortBy (comparing sortKey) warnings
+      reportProjectParseWarnings verbosity fpath (map (showPWarningWithSource . fmap renderProjectFileSource) sortedWarnings)
+      return x
+    Left (_, errors) -> do
+      dieWithException verbosity $ ProjectConfigParseFailure $ ProjectConfigParseError errors warnings
 
-      readExtensionFile =
-        reportParseResult verbosity extensionDescription extensionFile
-          =<< parseProject extensionFile distDownloadSrcDirectory httpTransport verbosity . ProjectConfigToParse
-          =<< BS.readFile extensionFile
+-- | Reads a named extended (with imports and conditionals) config file in the given project root dir, or returns empty.
+parseProjectFileSkeletonLegacy :: Verbosity -> HttpTransport -> DistDirLayout -> String -> String -> FilePath -> IO (OldParser.ProjectParseResult ProjectConfigSkeleton)
+parseProjectFileSkeletonLegacy verbosity httpTransport distDirLayout extensionName extensionDescription extensionFile =
+  parseProject extensionFile (distDownloadSrcDirectory distDirLayout) httpTransport verbosity . ProjectConfigToParse
+    =<< BS.readFile extensionFile
+
+parseProjectFileSkeletonParsec :: Verbosity -> HttpTransport -> DistDirLayout -> String -> String -> FilePath -> IO (Parsec.ParseResult ProjectFileSource ProjectConfigSkeleton, BS.ByteString)
+parseProjectFileSkeletonParsec verbosity httpTransport distDirLayout extensionName extensionDescription extensionFile = do
+  bs <- BS.readFile extensionFile
+  res <- Parsec.parseProject extensionFile (distDownloadSrcDirectory distDirLayout) httpTransport verbosity $ ProjectConfigToParse bs
+  return (res, bs)
 
 -- | Render the 'ProjectConfig' format.
 --
@@ -881,23 +1013,27 @@ readGlobalConfig verbosity configFileFlag = do
   monitorFiles [monitorFileHashed configFile]
   return (convertLegacyGlobalConfig config)
 
-reportProjectParseWarnings :: Verbosity -> FilePath -> [ProjectParseWarning] -> IO ()
-reportProjectParseWarnings verbosity projectFile warnings =
-  unless (null warnings) $
-    let msgs =
-          [ OldParser.showPWarning pFilename w
-          | (p, w) <- warnings
-          , let pFilename = fst $ unconsProjectConfigPath p
-          ]
-     in noticeDoc verbosity $
-          vcat
-            [ (text "Warnings found while parsing the project file" <> comma) <+> (text (takeFileName projectFile) <> colon)
-            , cat [nest 1 $ text "-" <+> text m | m <- ordNub msgs]
-            ]
+reportProjectParseWarningsLegacy :: Verbosity -> FilePath -> [ProjectParseWarning] -> IO ()
+reportProjectParseWarningsLegacy verbosity projectFile warnings =
+  let msgs =
+        [ OldParser.showPWarning pFilename w
+        | (p, w) <- warnings
+        , let pFilename = fst $ unconsProjectConfigPath p
+        ]
+   in reportProjectParseWarnings verbosity projectFile msgs
+
+reportProjectParseWarnings :: Verbosity -> FilePath -> [String] -> IO ()
+reportProjectParseWarnings verbosity projectFile msgs =
+  unless (null msgs) $
+    noticeDoc verbosity $
+      vcat
+        [ (text "Warnings found while parsing the project file" <> comma) <+> (text (takeFileName projectFile) <> colon)
+        , cat [nest 1 $ text "-" <+> text m | m <- ordNub msgs]
+        ]
 
 reportParseResult :: Verbosity -> String -> FilePath -> OldParser.ProjectParseResult ProjectConfigSkeleton -> IO ProjectConfigSkeleton
 reportParseResult verbosity _filetype projectFile (OldParser.ProjectParseOk warnings x) = do
-  reportProjectParseWarnings verbosity projectFile warnings
+  reportProjectParseWarningsLegacy verbosity projectFile warnings
   return x
 reportParseResult verbosity filetype projectFile (OldParser.ProjectParseFailed (ProjectParseError snippet rootOrImportee err)) = do
   let (line, msg) = OldParser.locatedErrorMsg err
@@ -906,7 +1042,7 @@ reportParseResult verbosity filetype projectFile (OldParser.ProjectParseFailed (
         maybe
           (projectFile, empty)
           ( \p ->
-              ( fst $ unconsProjectConfigPath p
+              ( currentProjectConfigPath p
               , if isTopLevelConfigPath p then empty else docProjectConfigPath p
               )
           )
@@ -1602,43 +1738,6 @@ mkSpecificSourcePackage location pkg =
       , srcpkgDescrOverride = Nothing
       }
 
--- | Errors reported upon failing to parse a @.cabal@ file.
-data CabalFileParseError
-  = CabalFileParseError
-      FilePath
-      -- ^ @.cabal@ file path
-      BS.ByteString
-      -- ^ @.cabal@ file contents
-      (NonEmpty PError)
-      -- ^ errors
-      (Maybe Version)
-      -- ^ We might discover the spec version the package needs
-      [PWarning]
-      -- ^ warnings
-
--- | Manual instance which skips file contents
-instance Show CabalFileParseError where
-  showsPrec d (CabalFileParseError fp _ es mv ws) =
-    showParen (d > 10) $
-      showString "CabalFileParseError"
-        . showChar ' '
-        . showsPrec 11 fp
-        . showChar ' '
-        . showsPrec 11 ("" :: String)
-        . showChar ' '
-        . showsPrec 11 es
-        . showChar ' '
-        . showsPrec 11 mv
-        . showChar ' '
-        . showsPrec 11 ws
-
-instance Exception CabalFileParseError where
-  displayException = renderCabalFileParseError
-
-renderCabalFileParseError :: CabalFileParseError -> String
-renderCabalFileParseError (CabalFileParseError filePath contents errors _ warnings) =
-  renderParseError filePath contents errors warnings
-
 -- | Wrapper for the @.cabal@ file parser. It reports warnings on higher
 -- verbosity levels and throws 'CabalFileParseError' on failure.
 readSourcePackageCabalFile
@@ -1659,10 +1758,10 @@ readSourcePackageCabalFile'
   -> BS.ByteString
   -> IO GenericPackageDescription
 readSourcePackageCabalFile' logWarnings pkgfilename content =
-  case runParseResult (parseGenericPackageDescription content) of
+  case runParseResult (withSource (PCabalFile (pkgfilename, content)) $ parseGenericPackageDescription content) of
     (warnings, Right pkg) -> do
       unless (null warnings) $
-        logWarnings (formatWarnings warnings)
+        logWarnings (formatWarnings . map (fmap renderCabalFileSource) $ warnings)
       return pkg
     (warnings, Left (mspecVersion, errors)) ->
       throwIO $ CabalFileParseError pkgfilename content errors mspecVersion warnings
@@ -1671,7 +1770,7 @@ readSourcePackageCabalFile' logWarnings pkgfilename content =
       "The package description file "
         ++ pkgfilename
         ++ " has warnings: "
-        ++ unlines (map (showPWarning pkgfilename) warnings)
+        ++ unlines (map showPWarningWithSource warnings)
 
 -- | When looking for a package's @.cabal@ file we can find none, or several,
 -- both of which are failures.
diff --git a/cabal-install/src/Distribution/Client/ProjectConfig/FieldGrammar.hs b/cabal-install/src/Distribution/Client/ProjectConfig/FieldGrammar.hs
new file mode 100644
index 00000000000..591bf0ba03d
--- /dev/null
+++ b/cabal-install/src/Distribution/Client/ProjectConfig/FieldGrammar.hs
@@ -0,0 +1,265 @@
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE RecordWildCards #-}
+
+-- | 'ProjectConfig' Field descriptions
+module Distribution.Client.ProjectConfig.FieldGrammar
+  ( projectConfigFieldGrammar
+  , packageConfigFieldGrammar
+  ) where
+
+import qualified Data.ByteString.Char8 as BS
+import qualified Data.Set as Set
+import Distribution.CabalSpecVersion (CabalSpecVersion (..))
+import Distribution.Client.CmdInstall.ClientInstallFlags (clientInstallFlagsGrammar)
+import qualified Distribution.Client.ProjectConfig.Lens as L
+import Distribution.Client.ProjectConfig.Types (PackageConfig (..), ProjectConfig (..), ProjectConfigBuildOnly (..), ProjectConfigProvenance (..), ProjectConfigShared (..))
+import Distribution.Client.Utils.Parsec
+import Distribution.Compat.Prelude
+import Distribution.FieldGrammar
+import Distribution.Simple.Flag
+import Distribution.Simple.InstallDirs
+import Distribution.Solver.Types.ConstraintSource (ConstraintSource (..))
+import Distribution.Solver.Types.ProjectConfigPath
+import Distribution.Types.PackageVersionConstraint (PackageVersionConstraint (..))
+
+projectConfigFieldGrammar :: ProjectConfigPath -> [String] -> ParsecFieldGrammar' ProjectConfig
+projectConfigFieldGrammar source knownPrograms =
+  ProjectConfig
+    <$> monoidalFieldAla "packages" (alaList' FSep Token) L.projectPackages
+    <*> monoidalFieldAla "optional-packages" (alaList' FSep Token) L.projectPackagesOptional
+    <*> pure mempty -- source-repository-package stanza
+    <*> monoidalFieldAla "extra-packages" formatPackageVersionConstraints L.projectPackagesNamed
+    <*> blurFieldGrammar L.projectConfigBuildOnly projectConfigBuildOnlyFieldGrammar
+    <*> blurFieldGrammar L.projectConfigShared (projectConfigSharedFieldGrammar source)
+    <*> pure provenance
+    <*> pure mempty
+    -- \^ PackageConfig to be applied to all packages, specified inside 'package *' stanza
+    <*> blurFieldGrammar L.projectConfigLocalPackages (packageConfigFieldGrammar knownPrograms)
+    -- \^ PackageConfig to be applied to locally built packages, specified not inside a stanza
+    <*> pure mempty
+  where
+    -- \^ PackageConfig applied to explicitly named packages
+    provenance = Set.singleton (Explicit source)
+
+formatPackageVersionConstraints :: [PackageVersionConstraint] -> List CommaVCat (Identity PackageVersionConstraint) PackageVersionConstraint
+formatPackageVersionConstraints = alaList CommaVCat
+
+projectConfigBuildOnlyFieldGrammar :: ParsecFieldGrammar' ProjectConfigBuildOnly
+projectConfigBuildOnlyFieldGrammar =
+  ProjectConfigBuildOnly
+    <$> optionalFieldDef "verbose" L.projectConfigVerbosity mempty
+    <*> pure mempty -- cli flag: projectConfigDryRun
+    <*> pure mempty -- cli flag: projectConfigOnlyDeps
+    <*> pure mempty -- cli flag: projectConfigOnlyDownload
+    <*> monoidalFieldAla "build-summary" (alaNubList VCat) L.projectConfigSummaryFile
+    <*> optionalFieldDef "build-log" L.projectConfigLogFile mempty
+    <*> optionalFieldDef "remote-build-reporting" L.projectConfigBuildReports mempty
+    <*> optionalFieldDef "report-planning-failure" L.projectConfigReportPlanningFailure mempty
+    <*> optionalFieldDefAla "symlink-bindir" (alaFlag FilePathNT) L.projectConfigSymlinkBinDir mempty
+    <*> optionalFieldDefAla "jobs" (alaFlag NumJobs) L.projectConfigNumJobs mempty
+    <*> optionalFieldDef "semaphore" L.projectConfigUseSemaphore mempty
+    <*> optionalFieldDef "keep-going" L.projectConfigKeepGoing mempty
+    <*> optionalFieldDef "offline" L.projectConfigOfflineMode mempty
+    <*> optionalFieldDef "haddock-keep-temp-files" L.projectConfigKeepTempFiles mempty
+    <*> optionalFieldDefAla "http-transport" (alaFlag Token) L.projectConfigHttpTransport mempty
+    <*> optionalFieldDef "ignore-expiry" L.projectConfigIgnoreExpiry mempty
+    <*> optionalFieldDefAla "remote-repo-cache" (alaFlag FilePathNT) L.projectConfigCacheDir mempty
+    <*> optionalFieldDefAla "logs-dir" (alaFlag FilePathNT) L.projectConfigLogsDir mempty
+    <*> blurFieldGrammar L.projectConfigClientInstallFlags clientInstallFlagsGrammar
+
+projectConfigSharedFieldGrammar :: ProjectConfigPath -> ParsecFieldGrammar' ProjectConfigShared
+projectConfigSharedFieldGrammar source =
+  ProjectConfigShared
+    <$> optionalFieldDefAla "builddir" (alaFlag FilePathNT) L.projectConfigDistDir mempty
+    <*> pure mempty -- cli flag: projectConfigConfigFile
+    <*> optionalFieldDefAla "project-dir" (alaFlag FilePathNT) L.projectConfigProjectDir mempty
+    <*> optionalFieldDefAla "project-file" (alaFlag FilePathNT) L.projectConfigProjectFile mempty
+    <*> pure mempty -- You can't set the parser type in the project file.
+    <*> optionalFieldDef "ignore-project" L.projectConfigIgnoreProject mempty
+    <*> optionalFieldDef "compiler" L.projectConfigHcFlavor mempty
+    <*> optionalFieldDefAla "with-compiler" (alaFlag FilePathNT) L.projectConfigHcPath mempty
+    <*> optionalFieldDefAla "with-hc-pkg" (alaFlag FilePathNT) L.projectConfigHcPkg mempty
+    <*> optionalFieldDef "doc-index-file" L.projectConfigHaddockIndex mempty
+    <*> blurFieldGrammar L.projectConfigInstallDirs installDirsGrammar
+    <*> monoidalFieldAla "package-dbs" (alaList' CommaFSep PackageDBNT) L.projectConfigPackageDBs
+    <*> pure mempty -- repository stanza for projectConfigRemoteRepos
+    <*> pure mempty -- repository stanza for projectConfigLocalNoIndexRepos
+    <*> monoidalField "active-repositories" L.projectConfigActiveRepos
+    <*> monoidalField "index-state" L.projectConfigIndexState
+    <*> optionalFieldDefAla "store-dir" (alaFlag FilePathNT) L.projectConfigStoreDir mempty
+    <*> monoidalFieldAla "constraints" (alaList' FSep ProjectConstraints) L.projectConfigConstraints
+      ^^^ (fmap . fmap) (\(userConstraint, _) -> (userConstraint, ConstraintSourceProjectConfig source))
+    <*> monoidalFieldAla "preferences" formatPackageVersionConstraints L.projectConfigPreferences
+    <*> optionalFieldDef "cabal-lib-version" L.projectConfigCabalVersion mempty
+    <*> optionalFieldDef "solver" L.projectConfigSolver mempty
+    <*> monoidalFieldAla "allow-older" AllowOlderNT L.projectConfigAllowOlder
+    <*> monoidalFieldAla "allow-newer" AllowNewerNT L.projectConfigAllowNewer
+    <*> optionalFieldDef "write-ghc-environment-files" L.projectConfigWriteGhcEnvironmentFilesPolicy mempty
+    <*> optionalFieldDefAla "max-backjumps" (alaFlag MaxBackjumps) L.projectConfigMaxBackjumps mempty
+    <*> optionalFieldDef "reorder-goals" L.projectConfigReorderGoals mempty
+    <*> optionalFieldDef "count-conflicts" L.projectConfigCountConflicts mempty
+    <*> optionalFieldDef "fine-grained-conflicts" L.projectConfigFineGrainedConflicts mempty
+    <*> optionalFieldDef "minimize-conflict-set" L.projectConfigMinimizeConflictSet mempty
+    <*> optionalFieldDef "strong-flags" L.projectConfigStrongFlags mempty
+    <*> optionalFieldDef "allow-boot-library-installs" L.projectConfigAllowBootLibInstalls mempty
+    <*> optionalFieldDef "reject-unconstrained-dependencies" L.projectConfigOnlyConstrained mempty
+    <*> optionalFieldDef "per-component" L.projectConfigPerComponent mempty
+    <*> optionalFieldDef "independent-goals" L.projectConfigIndependentGoals mempty
+    <*> optionalFieldDef "prefer-oldest" L.projectConfigPreferOldest mempty
+    <*> monoidalFieldAla "extra-prog-path-shared-only" (alaNubList' FSep FilePathNT) L.projectConfigProgPathExtra
+    <*> optionalFieldDef "multi-repl" L.projectConfigMultiRepl mempty
+
+packageConfigFieldGrammar :: [String] -> ParsecFieldGrammar' PackageConfig
+packageConfigFieldGrammar knownPrograms =
+  mkPackageConfig
+    <$> optionalFieldDef "haddock-all" noopLens mempty
+      ^^^ hiddenField
+    <*> pure mempty -- program-options stanza
+    <*> pure mempty -- program-locations stanza
+    <*> monoidalFieldAla "extra-prog-path" (alaNubList' FSep FilePathNT) L.packageConfigProgramPathExtra
+    <*> monoidalField "flags" L.packageConfigFlagAssignment
+    <*> optionalFieldDef "library-vanilla" L.packageConfigVanillaLib mempty
+    <*> optionalFieldDef "shared" L.packageConfigSharedLib mempty
+    <*> optionalFieldDef "static" L.packageConfigStaticLib mempty
+    <*> optionalFieldDef "executable-dynamic" L.packageConfigDynExe mempty
+    <*> optionalFieldDef "executable-static" L.packageConfigFullyStaticExe mempty
+    <*> optionalFieldDef "profiling" L.packageConfigProf mempty
+    <*> optionalFieldDef "library-profiling" L.packageConfigProfLib mempty
+    <*> optionalFieldDef "profiling-shared" L.packageConfigProfShared mempty
+    <*> optionalFieldDef "executable-profiling" L.packageConfigProfExe mempty
+    <*> optionalFieldDef "profiling-detail" L.packageConfigProfDetail mempty
+    <*> optionalFieldDef "library-profiling-detail" L.packageConfigProfLibDetail mempty
+    <*> monoidalFieldAla "configure-options" (alaList' NoCommaFSep Token) L.packageConfigConfigureArgs
+    <*> optionalFieldDef "optimization" L.packageConfigOptimization mempty
+    <*> optionalFieldDef "program-prefix" L.packageConfigProgPrefix mempty
+    <*> optionalFieldDef "program-suffix" L.packageConfigProgSuffix mempty
+    <*> monoidalFieldAla "extra-lib-dirs" (alaList' FSep FilePathNT) L.packageConfigExtraLibDirs
+    <*> monoidalFieldAla "extra-lib-dirs-static" (alaList' FSep FilePathNT) L.packageConfigExtraLibDirsStatic
+    <*> monoidalFieldAla "extra-framework-dirs" (alaList' FSep FilePathNT) L.packageConfigExtraFrameworkDirs
+    <*> monoidalFieldAla "extra-include-dirs" (alaList' FSep FilePathNT) L.packageConfigExtraIncludeDirs
+    <*> optionalFieldDef "library-for-ghci" L.packageConfigGHCiLib mempty
+    <*> optionalFieldDef "split-sections" L.packageConfigSplitSections mempty
+    <*> optionalFieldDef "split-objs" L.packageConfigSplitObjs mempty
+    <*> optionalFieldDef "executable-stripping" L.packageConfigStripExes mempty
+    <*> optionalFieldDef "library-stripping" L.packageConfigStripLibs mempty
+    <*> optionalFieldDef "tests" L.packageConfigTests mempty
+    <*> optionalFieldDef "benchmarks" L.packageConfigBenchmarks mempty
+    <*> packageConfigCoverageGrammar
+    <*> optionalFieldDef "relocatable" L.packageConfigRelocatable mempty
+    <*> optionalFieldDef "debug-info" L.packageConfigDebugInfo mempty
+    <*> optionalFieldDef "build-info" L.packageConfigDumpBuildInfo mempty
+    <*> optionalFieldDef "run-tests" L.packageConfigRunTests mempty
+    <*> optionalFieldDef "documentation" L.packageConfigDocumentation mempty
+    <*> optionalFieldDef "haddock-hoogle" L.packageConfigHaddockHoogle mempty
+    <*> optionalFieldDef "haddock-html" L.packageConfigHaddockHtml mempty
+    <*> optionalFieldDefAla "haddock-html-location" (alaFlag Token) L.packageConfigHaddockHtmlLocation mempty
+    <*> optionalFieldDef "haddock-foreign-libraries" L.packageConfigHaddockForeignLibs mempty
+    <*> optionalFieldDef "haddock-executables" L.packageConfigHaddockExecutables mempty
+    <*> optionalFieldDef "haddock-tests" L.packageConfigHaddockTestSuites mempty
+    <*> optionalFieldDef "haddock-benchmarks" L.packageConfigHaddockBenchmarks mempty
+    <*> optionalFieldDef "haddock-internal" L.packageConfigHaddockInternal mempty
+    <*> optionalFieldDefAla "haddock-css" (alaFlag FilePathNT) L.packageConfigHaddockCss mempty
+    <*> optionalFieldDef "haddock-hyperlink-source" L.packageConfigHaddockLinkedSource mempty
+    <*> optionalFieldDef "haddock-quickjump" L.packageConfigHaddockQuickJump mempty
+    <*> optionalFieldDefAla "haddock-hscolour-css" (alaFlag FilePathNT) L.packageConfigHaddockHscolourCss mempty
+    <*> optionalFieldDef "haddock-contents-location" L.packageConfigHaddockContents mempty
+    <*> optionalFieldDef "haddock-index-location" L.packageConfigHaddockIndex mempty
+    <*> optionalFieldDefAla "haddock-base-url" (alaFlag Token) L.packageConfigHaddockBaseUrl mempty
+    <*> optionalFieldDefAla "haddock-resources-dir" (alaFlag Token) L.packageConfigHaddockResourcesDir mempty
+    <*> optionalFieldDefAla "haddock-output-dir" (alaFlag FilePathNT) L.packageConfigHaddockOutputDir mempty
+    <*> optionalFieldDef "haddock-use-unicode" L.packageConfigHaddockUseUnicode mempty
+    <*> optionalFieldDef "haddock-for-hackage" L.packageConfigHaddockForHackage mempty
+    <*> optionalFieldDef "test-log" L.packageConfigTestHumanLog mempty
+    <*> optionalFieldDef "test-machine-log" L.packageConfigTestMachineLog mempty
+    <*> optionalFieldDef "test-show-details" L.packageConfigTestShowDetails mempty
+    <*> optionalFieldDef "test-keep-tix-files" L.packageConfigTestKeepTix mempty
+    <*> optionalFieldDefAla "test-wrapper" (alaFlag FilePathNT) L.packageConfigTestWrapper mempty
+    <*> optionalFieldDef "test-fail-when-no-test-suites" L.packageConfigTestFailWhenNoTestSuites mempty
+    <*> monoidalFieldAla "test-options" (alaList NoCommaFSep) L.packageConfigTestTestOptions
+    <*> monoidalFieldAla "benchmark-options" (alaList NoCommaFSep) L.packageConfigBenchmarkOptions
+    -- A PackageConfig may contain -options and -location fields inside a package * (projectConfigAllPackages) or package <name> stanza (packageConfigSpecificPackage).
+    -- When declared at top level (packageConfigLocalPackages), the PackageConfig must contain a program-options stanza/program-locations for these fields.
+    <* traverse_ (knownField . BS.pack . (<> "-options")) knownPrograms
+    <* traverse_ (knownField . BS.pack . (<> "-location")) knownPrograms
+  where
+    noopLens f s = s <$ f mempty
+    mkPackageConfig
+      haddockAll
+      packageConfigProgramPaths
+      packageConfigProgramArgs
+      packageConfigProgramPathExtra
+      packageConfigFlagAssignment
+      packageConfigVanillaLib
+      packageConfigSharedLib
+      packageConfigStaticLib
+      packageConfigDynExe
+      packageConfigFullyStaticExe
+      packageConfigProf
+      packageConfigProfLib
+      packageConfigProfShared
+      packageConfigProfExe
+      packageConfigProfDetail
+      packageConfigProfLibDetail
+      packageConfigConfigureArgs
+      packageConfigOptimization
+      packageConfigProgPrefix
+      packageConfigProgSuffix
+      packageConfigExtraLibDirs
+      packageConfigExtraLibDirsStatic
+      packageConfigExtraFrameworkDirs
+      packageConfigExtraIncludeDirs
+      packageConfigGHCiLib
+      packageConfigSplitSections
+      packageConfigSplitObjs
+      packageConfigStripExes
+      packageConfigStripLibs
+      packageConfigTests
+      packageConfigBenchmarks
+      packageConfigCoverage
+      packageConfigRelocatable
+      packageConfigDebugInfo
+      packageConfigDumpBuildInfo
+      packageConfigRunTests
+      packageConfigDocumentation
+      packageConfigHaddockHoogle
+      packageConfigHaddockHtml
+      packageConfigHaddockHtmlLocation
+      packageConfigHaddockForeignLibs'
+      packageConfigHaddockExecutables'
+      packageConfigHaddockTestSuites'
+      packageConfigHaddockBenchmarks'
+      packageConfigHaddockInternal
+      packageConfigHaddockCss
+      packageConfigHaddockLinkedSource
+      packageConfigHaddockQuickJump
+      packageConfigHaddockHscolourCss
+      packageConfigHaddockContents
+      packageConfigHaddockIndex
+      packageConfigHaddockBaseUrl
+      packageConfigHaddockResourcesDir
+      packageConfigHaddockOutputDir
+      packageConfigHaddockUseUnicode
+      packageConfigHaddockForHackage
+      packageConfigTestHumanLog
+      packageConfigTestMachineLog
+      packageConfigTestShowDetails
+      packageConfigTestKeepTix
+      packageConfigTestWrapper
+      packageConfigTestFailWhenNoTestSuites
+      packageConfigTestTestOptions
+      packageConfigBenchmarkOptions =
+        PackageConfig
+          { -- The haddock-al` field provides a default value, but explicit declarations can override it
+            packageConfigHaddockForeignLibs = haddockAll <> packageConfigHaddockForeignLibs'
+          , packageConfigHaddockExecutables = haddockAll <> packageConfigHaddockExecutables'
+          , packageConfigHaddockTestSuites = haddockAll <> packageConfigHaddockTestSuites'
+          , packageConfigHaddockBenchmarks = haddockAll <> packageConfigHaddockBenchmarks'
+          , ..
+          }
+
+packageConfigCoverageGrammar :: ParsecFieldGrammar PackageConfig (Distribution.Simple.Flag.Flag Bool)
+packageConfigCoverageGrammar =
+  (<>)
+    <$> optionalFieldDef "coverage" L.packageConfigCoverage mempty
+    <*> optionalFieldDef "library-coverage" L.packageConfigCoverage mempty
+      ^^^ deprecatedSince CabalSpecV1_22 "Please use 'coverage' field instead."
diff --git a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
index 2e24a493d0e..32b3670b479 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig/Legacy.hs
@@ -771,6 +771,7 @@ convertLegacyAllPackageFlags globalFlags configFlags configExFlags installFlags
       { flagProjectDir = projectConfigProjectDir
       , flagProjectFile = projectConfigProjectFile
       , flagIgnoreProject = projectConfigIgnoreProject
+      , flagProjectFileParser = projectConfigProjectFileParser
       } = projectFlags
 
 -- | Helper used by other conversion functions that returns the
@@ -1070,6 +1071,7 @@ convertToLegacySharedConfig
           { flagProjectDir = projectConfigProjectDir
           , flagProjectFile = projectConfigProjectFile
           , flagIgnoreProject = projectConfigIgnoreProject
+          , flagProjectFileParser = projectConfigProjectFileParser
           }
 
 convertToLegacyAllPackageConfig :: ProjectConfig -> LegacyPackageConfig
diff --git a/cabal-install/src/Distribution/Client/ProjectConfig/Lens.hs b/cabal-install/src/Distribution/Client/ProjectConfig/Lens.hs
new file mode 100644
index 00000000000..03e05835cd6
--- /dev/null
+++ b/cabal-install/src/Distribution/Client/ProjectConfig/Lens.hs
@@ -0,0 +1,557 @@
+module Distribution.Client.ProjectConfig.Lens where
+
+import Distribution.Client.BuildReports.Types (ReportLevel (..))
+import Distribution.Client.CmdInstall.ClientInstallFlags (ClientInstallFlags (..))
+import Distribution.Client.Dependency.Types (PreSolver (..))
+import Distribution.Client.IndexUtils.ActiveRepos
+  ( ActiveRepos
+  )
+import Distribution.Client.IndexUtils.IndexState (TotalIndexState)
+import Distribution.Client.ProjectConfig.Types (MapLast, MapMappend, PackageConfig, ProjectConfig (..), ProjectConfigBuildOnly (..), ProjectConfigProvenance, ProjectConfigShared)
+import qualified Distribution.Client.ProjectConfig.Types as T
+import Distribution.Client.Targets (UserConstraint)
+import Distribution.Client.Types.AllowNewer (AllowNewer, AllowOlder)
+import Distribution.Client.Types.Repo (LocalRepo, RemoteRepo)
+import Distribution.Client.Types.SourceRepo (SourceRepoList)
+import Distribution.Client.Types.WriteGhcEnvironmentFilesPolicy (WriteGhcEnvironmentFilesPolicy)
+import Distribution.Compat.Lens
+import Distribution.Compat.Prelude
+import Distribution.Compiler (CompilerFlavor (..))
+import Distribution.Package
+  ( PackageName
+  )
+import Distribution.PackageDescription
+  ( FlagAssignment
+  )
+import Distribution.Simple.Compiler
+  ( DebugInfoLevel (..)
+  , OptimisationLevel (..)
+  , PackageDBCWD
+  , ProfDetailLevel
+  )
+import Distribution.Simple.InstallDirs
+  ( InstallDirs
+  , PathTemplate
+  )
+import Distribution.Simple.Setup
+  ( DumpBuildInfo (..)
+  , Flag
+  , HaddockTarget (..)
+  , TestShowDetails (..)
+  )
+import Distribution.Solver.Types.ConstraintSource (ConstraintSource)
+import Distribution.Solver.Types.Settings
+  ( AllowBootLibInstalls (..)
+  , CountConflicts (..)
+  , FineGrainedConflicts (..)
+  , IndependentGoals (..)
+  , MinimizeConflictSet (..)
+  , OnlyConstrained (..)
+  , PreferOldest (..)
+  , ReorderGoals (..)
+  , StrongFlags (..)
+  )
+import Distribution.Types.PackageVersionConstraint
+  ( PackageVersionConstraint
+  )
+import Distribution.Types.Version (Version)
+import Distribution.Utils.NubList
+  ( NubList
+  )
+import Distribution.Verbosity
+
+projectPackages :: Lens' ProjectConfig [String]
+projectPackages f s = fmap (\x -> s{T.projectPackages = x}) (f (T.projectPackages s))
+{-# INLINEABLE projectPackages #-}
+
+projectPackagesOptional :: Lens' ProjectConfig [String]
+projectPackagesOptional f s = fmap (\x -> s{T.projectPackagesOptional = x}) (f (T.projectPackagesOptional s))
+{-# INLINEABLE projectPackagesOptional #-}
+
+projectPackagesRepo :: Lens' ProjectConfig [SourceRepoList]
+projectPackagesRepo f s = fmap (\x -> s{T.projectPackagesRepo = x}) (f (T.projectPackagesRepo s))
+{-# INLINEABLE projectPackagesRepo #-}
+
+projectPackagesNamed :: Lens' ProjectConfig [PackageVersionConstraint]
+projectPackagesNamed f s = fmap (\x -> s{T.projectPackagesNamed = x}) (f (T.projectPackagesNamed s))
+{-# INLINEABLE projectPackagesNamed #-}
+
+projectConfigBuildOnly :: Lens' ProjectConfig ProjectConfigBuildOnly
+projectConfigBuildOnly f s = fmap (\x -> s{T.projectConfigBuildOnly = x}) (f (T.projectConfigBuildOnly s))
+{-# INLINEABLE projectConfigBuildOnly #-}
+
+projectConfigShared :: Lens' ProjectConfig ProjectConfigShared
+projectConfigShared f s = fmap (\x -> s{T.projectConfigShared = x}) (f (T.projectConfigShared s))
+{-# INLINEABLE projectConfigShared #-}
+
+projectConfigProvenance :: Lens' ProjectConfig (Set ProjectConfigProvenance)
+projectConfigProvenance f s = fmap (\x -> s{T.projectConfigProvenance = x}) (f (T.projectConfigProvenance s))
+{-# INLINEABLE projectConfigProvenance #-}
+
+projectConfigAllPackages :: Lens' ProjectConfig PackageConfig
+projectConfigAllPackages f s = fmap (\x -> s{T.projectConfigAllPackages = x}) (f (T.projectConfigAllPackages s))
+{-# INLINEABLE projectConfigAllPackages #-}
+
+projectConfigLocalPackages :: Lens' ProjectConfig PackageConfig
+projectConfigLocalPackages f s = fmap (\x -> s{T.projectConfigLocalPackages = x}) (f (T.projectConfigLocalPackages s))
+{-# INLINEABLE projectConfigLocalPackages #-}
+
+projectConfigSpecificPackage :: Lens' ProjectConfig (MapMappend PackageName PackageConfig)
+projectConfigSpecificPackage f s = fmap (\x -> s{T.projectConfigSpecificPackage = x}) (f (T.projectConfigSpecificPackage s))
+{-# INLINEABLE projectConfigSpecificPackage #-}
+
+projectConfigVerbosity :: Lens' ProjectConfigBuildOnly (Flag Verbosity)
+projectConfigVerbosity f s = fmap (\x -> s{T.projectConfigVerbosity = x}) (f (T.projectConfigVerbosity s))
+{-# INLINEABLE projectConfigVerbosity #-}
+
+projectConfigSummaryFile :: Lens' ProjectConfigBuildOnly (NubList PathTemplate)
+projectConfigSummaryFile f s = fmap (\x -> s{T.projectConfigSummaryFile = x}) (f (T.projectConfigSummaryFile s))
+{-# INLINEABLE projectConfigSummaryFile #-}
+
+projectConfigLogFile :: Lens' ProjectConfigBuildOnly (Flag PathTemplate)
+projectConfigLogFile f s = fmap (\x -> s{T.projectConfigLogFile = x}) (f (T.projectConfigLogFile s))
+{-# INLINEABLE projectConfigLogFile #-}
+
+projectConfigBuildReports :: Lens' ProjectConfigBuildOnly (Flag ReportLevel)
+projectConfigBuildReports f s = fmap (\x -> s{T.projectConfigBuildReports = x}) (f (T.projectConfigBuildReports s))
+{-# INLINEABLE projectConfigBuildReports #-}
+
+projectConfigReportPlanningFailure :: Lens' ProjectConfigBuildOnly (Flag Bool)
+projectConfigReportPlanningFailure f s = fmap (\x -> s{T.projectConfigReportPlanningFailure = x}) (f (T.projectConfigReportPlanningFailure s))
+{-# INLINEABLE projectConfigReportPlanningFailure #-}
+
+projectConfigSymlinkBinDir :: Lens' ProjectConfigBuildOnly (Flag FilePath)
+projectConfigSymlinkBinDir f s = fmap (\x -> s{T.projectConfigSymlinkBinDir = x}) (f (T.projectConfigSymlinkBinDir s))
+{-# INLINEABLE projectConfigSymlinkBinDir #-}
+
+projectConfigNumJobs :: Lens' ProjectConfigBuildOnly (Flag (Maybe Int))
+projectConfigNumJobs f s = fmap (\x -> s{T.projectConfigNumJobs = x}) (f (T.projectConfigNumJobs s))
+{-# INLINEABLE projectConfigNumJobs #-}
+
+projectConfigUseSemaphore :: Lens' ProjectConfigBuildOnly (Flag Bool)
+projectConfigUseSemaphore f s = fmap (\x -> s{T.projectConfigUseSemaphore = x}) (f (T.projectConfigUseSemaphore s))
+{-# INLINEABLE projectConfigUseSemaphore #-}
+
+projectConfigKeepGoing :: Lens' ProjectConfigBuildOnly (Flag Bool)
+projectConfigKeepGoing f s = fmap (\x -> s{T.projectConfigKeepGoing = x}) (f (T.projectConfigKeepGoing s))
+{-# INLINEABLE projectConfigKeepGoing #-}
+
+projectConfigOfflineMode :: Lens' ProjectConfigBuildOnly (Flag Bool)
+projectConfigOfflineMode f s = fmap (\x -> s{T.projectConfigOfflineMode = x}) (f (T.projectConfigOfflineMode s))
+{-# INLINEABLE projectConfigOfflineMode #-}
+
+projectConfigKeepTempFiles :: Lens' ProjectConfigBuildOnly (Flag Bool)
+projectConfigKeepTempFiles f s = fmap (\x -> s{T.projectConfigKeepTempFiles = x}) (f (T.projectConfigKeepTempFiles s))
+{-# INLINEABLE projectConfigKeepTempFiles #-}
+
+projectConfigHttpTransport :: Lens' ProjectConfigBuildOnly (Flag String)
+projectConfigHttpTransport f s = fmap (\x -> s{T.projectConfigHttpTransport = x}) (f (T.projectConfigHttpTransport s))
+{-# INLINEABLE projectConfigHttpTransport #-}
+
+projectConfigIgnoreExpiry :: Lens' ProjectConfigBuildOnly (Flag Bool)
+projectConfigIgnoreExpiry f s = fmap (\x -> s{T.projectConfigIgnoreExpiry = x}) (f (T.projectConfigIgnoreExpiry s))
+{-# INLINEABLE projectConfigIgnoreExpiry #-}
+
+projectConfigCacheDir :: Lens' ProjectConfigBuildOnly (Flag FilePath)
+projectConfigCacheDir f s = fmap (\x -> s{T.projectConfigCacheDir = x}) (f (T.projectConfigCacheDir s))
+{-# INLINEABLE projectConfigCacheDir #-}
+
+projectConfigLogsDir :: Lens' ProjectConfigBuildOnly (Flag FilePath)
+projectConfigLogsDir f s = fmap (\x -> s{T.projectConfigLogsDir = x}) (f (T.projectConfigLogsDir s))
+{-# INLINEABLE projectConfigLogsDir #-}
+
+projectConfigClientInstallFlags :: Lens' ProjectConfigBuildOnly (ClientInstallFlags)
+projectConfigClientInstallFlags f s = fmap (\x -> s{T.projectConfigClientInstallFlags = x}) (f (T.projectConfigClientInstallFlags s))
+{-# INLINEABLE projectConfigClientInstallFlags #-}
+
+projectConfigDistDir :: Lens' ProjectConfigShared (Flag FilePath)
+projectConfigDistDir f s = fmap (\x -> s{T.projectConfigDistDir = x}) (f (T.projectConfigDistDir s))
+{-# INLINEABLE projectConfigDistDir #-}
+
+projectConfigProjectDir :: Lens' ProjectConfigShared (Flag FilePath)
+projectConfigProjectDir f s = fmap (\x -> s{T.projectConfigProjectDir = x}) (f (T.projectConfigProjectDir s))
+{-# INLINEABLE projectConfigProjectDir #-}
+
+projectConfigStoreDir :: Lens' ProjectConfigShared (Flag FilePath)
+projectConfigStoreDir f s = fmap (\x -> s{T.projectConfigStoreDir = x}) (f (T.projectConfigStoreDir s))
+{-# INLINEABLE projectConfigStoreDir #-}
+
+projectConfigPerComponent :: Lens' ProjectConfigShared (Flag Bool)
+projectConfigPerComponent f s = fmap (\x -> s{T.projectConfigPerComponent = x}) (f (T.projectConfigPerComponent s))
+{-# INLINEABLE projectConfigPerComponent #-}
+
+projectConfigIndependentGoals :: Lens' ProjectConfigShared (Flag IndependentGoals)
+projectConfigIndependentGoals f s = fmap (\x -> s{T.projectConfigIndependentGoals = x}) (f (T.projectConfigIndependentGoals s))
+{-# INLINEABLE projectConfigIndependentGoals #-}
+
+projectConfigProjectFile :: Lens' ProjectConfigShared (Flag FilePath)
+projectConfigProjectFile f s = fmap (\x -> s{T.projectConfigProjectFile = x}) (f (T.projectConfigProjectFile s))
+{-# INLINEABLE projectConfigProjectFile #-}
+
+projectConfigIgnoreProject :: Lens' ProjectConfigShared (Flag Bool)
+projectConfigIgnoreProject f s = fmap (\x -> s{T.projectConfigIgnoreProject = x}) (f (T.projectConfigIgnoreProject s))
+{-# INLINEABLE projectConfigIgnoreProject #-}
+
+projectConfigHcFlavor :: Lens' ProjectConfigShared (Flag CompilerFlavor)
+projectConfigHcFlavor f s = fmap (\x -> s{T.projectConfigHcFlavor = x}) (f (T.projectConfigHcFlavor s))
+{-# INLINEABLE projectConfigHcFlavor #-}
+
+projectConfigHcPath :: Lens' ProjectConfigShared (Flag FilePath)
+projectConfigHcPath f s = fmap (\x -> s{T.projectConfigHcPath = x}) (f (T.projectConfigHcPath s))
+{-# INLINEABLE projectConfigHcPath #-}
+
+projectConfigHcPkg :: Lens' ProjectConfigShared (Flag FilePath)
+projectConfigHcPkg f s = fmap (\x -> s{T.projectConfigHcPkg = x}) (f (T.projectConfigHcPkg s))
+{-# INLINEABLE projectConfigHcPkg #-}
+
+projectConfigHaddockIndex :: Lens' ProjectConfigShared (Flag PathTemplate)
+projectConfigHaddockIndex f s = fmap (\x -> s{T.projectConfigHaddockIndex = x}) (f (T.projectConfigHaddockIndex s))
+{-# INLINEABLE projectConfigHaddockIndex #-}
+
+projectConfigInstallDirs :: Lens' ProjectConfigShared (InstallDirs (Flag PathTemplate))
+projectConfigInstallDirs f s = fmap (\x -> s{T.projectConfigInstallDirs = x}) (f (T.projectConfigInstallDirs s))
+{-# INLINEABLE projectConfigInstallDirs #-}
+
+projectConfigPackageDBs :: Lens' ProjectConfigShared [Maybe PackageDBCWD]
+projectConfigPackageDBs f s = fmap (\x -> s{T.projectConfigPackageDBs = x}) (f (T.projectConfigPackageDBs s))
+{-# INLINEABLE projectConfigPackageDBs #-}
+
+projectConfigLocalNoIndexRepos :: Lens' ProjectConfigShared (NubList LocalRepo)
+projectConfigLocalNoIndexRepos f s = fmap (\x -> s{T.projectConfigLocalNoIndexRepos = x}) (f (T.projectConfigLocalNoIndexRepos s))
+{-# INLINEABLE projectConfigLocalNoIndexRepos #-}
+
+projectConfigRemoteRepos :: Lens' ProjectConfigShared (NubList RemoteRepo)
+projectConfigRemoteRepos f s = fmap (\x -> s{T.projectConfigRemoteRepos = x}) (f (T.projectConfigRemoteRepos s))
+{-# INLINEABLE projectConfigRemoteRepos #-}
+
+projectConfigActiveRepos :: Lens' ProjectConfigShared (Flag ActiveRepos)
+projectConfigActiveRepos f s = fmap (\x -> s{T.projectConfigActiveRepos = x}) (f (T.projectConfigActiveRepos s))
+{-# INLINEABLE projectConfigActiveRepos #-}
+
+projectConfigIndexState :: Lens' ProjectConfigShared (Flag TotalIndexState)
+projectConfigIndexState f s = fmap (\x -> s{T.projectConfigIndexState = x}) (f (T.projectConfigIndexState s))
+{-# INLINEABLE projectConfigIndexState #-}
+
+projectConfigConstraints :: Lens' ProjectConfigShared [(UserConstraint, ConstraintSource)]
+projectConfigConstraints f s = fmap (\x -> s{T.projectConfigConstraints = x}) (f (T.projectConfigConstraints s))
+{-# INLINEABLE projectConfigConstraints #-}
+
+projectConfigPreferences :: Lens' ProjectConfigShared [PackageVersionConstraint]
+projectConfigPreferences f s = fmap (\x -> s{T.projectConfigPreferences = x}) (f (T.projectConfigPreferences s))
+{-# INLINEABLE projectConfigPreferences #-}
+
+projectConfigCabalVersion :: Lens' ProjectConfigShared (Flag Version)
+projectConfigCabalVersion f s = fmap (\x -> s{T.projectConfigCabalVersion = x}) (f (T.projectConfigCabalVersion s))
+{-# INLINEABLE projectConfigCabalVersion #-}
+
+projectConfigSolver :: Lens' ProjectConfigShared (Flag PreSolver)
+projectConfigSolver f s = fmap (\x -> s{T.projectConfigSolver = x}) (f (T.projectConfigSolver s))
+{-# INLINEABLE projectConfigSolver #-}
+
+projectConfigAllowOlder :: Lens' ProjectConfigShared (Maybe AllowOlder)
+projectConfigAllowOlder f s = fmap (\x -> s{T.projectConfigAllowOlder = x}) (f (T.projectConfigAllowOlder s))
+{-# INLINEABLE projectConfigAllowOlder #-}
+
+projectConfigAllowNewer :: Lens' ProjectConfigShared (Maybe AllowNewer)
+projectConfigAllowNewer f s = fmap (\x -> s{T.projectConfigAllowNewer = x}) (f (T.projectConfigAllowNewer s))
+{-# INLINEABLE projectConfigAllowNewer #-}
+
+projectConfigWriteGhcEnvironmentFilesPolicy :: Lens' ProjectConfigShared (Flag WriteGhcEnvironmentFilesPolicy)
+projectConfigWriteGhcEnvironmentFilesPolicy f s = fmap (\x -> s{T.projectConfigWriteGhcEnvironmentFilesPolicy = x}) (f (T.projectConfigWriteGhcEnvironmentFilesPolicy s))
+{-# INLINEABLE projectConfigWriteGhcEnvironmentFilesPolicy #-}
+
+projectConfigMaxBackjumps :: Lens' ProjectConfigShared (Flag Int)
+projectConfigMaxBackjumps f s = fmap (\x -> s{T.projectConfigMaxBackjumps = x}) (f (T.projectConfigMaxBackjumps s))
+{-# INLINEABLE projectConfigMaxBackjumps #-}
+
+projectConfigReorderGoals :: Lens' ProjectConfigShared (Flag ReorderGoals)
+projectConfigReorderGoals f s = fmap (\x -> s{T.projectConfigReorderGoals = x}) (f (T.projectConfigReorderGoals s))
+{-# INLINEABLE projectConfigReorderGoals #-}
+
+projectConfigCountConflicts :: Lens' ProjectConfigShared (Flag CountConflicts)
+projectConfigCountConflicts f s = fmap (\x -> s{T.projectConfigCountConflicts = x}) (f (T.projectConfigCountConflicts s))
+{-# INLINEABLE projectConfigCountConflicts #-}
+
+projectConfigFineGrainedConflicts :: Lens' ProjectConfigShared (Flag FineGrainedConflicts)
+projectConfigFineGrainedConflicts f s = fmap (\x -> s{T.projectConfigFineGrainedConflicts = x}) (f (T.projectConfigFineGrainedConflicts s))
+{-# INLINEABLE projectConfigFineGrainedConflicts #-}
+
+projectConfigMinimizeConflictSet :: Lens' ProjectConfigShared (Flag MinimizeConflictSet)
+projectConfigMinimizeConflictSet f s = fmap (\x -> s{T.projectConfigMinimizeConflictSet = x}) (f (T.projectConfigMinimizeConflictSet s))
+{-# INLINEABLE projectConfigMinimizeConflictSet #-}
+
+projectConfigStrongFlags :: Lens' ProjectConfigShared (Flag StrongFlags)
+projectConfigStrongFlags f s = fmap (\x -> s{T.projectConfigStrongFlags = x}) (f (T.projectConfigStrongFlags s))
+{-# INLINEABLE projectConfigStrongFlags #-}
+
+projectConfigAllowBootLibInstalls :: Lens' ProjectConfigShared (Flag AllowBootLibInstalls)
+projectConfigAllowBootLibInstalls f s = fmap (\x -> s{T.projectConfigAllowBootLibInstalls = x}) (f (T.projectConfigAllowBootLibInstalls s))
+{-# INLINEABLE projectConfigAllowBootLibInstalls #-}
+
+projectConfigOnlyConstrained :: Lens' ProjectConfigShared (Flag OnlyConstrained)
+projectConfigOnlyConstrained f s = fmap (\x -> s{T.projectConfigOnlyConstrained = x}) (f (T.projectConfigOnlyConstrained s))
+{-# INLINEABLE projectConfigOnlyConstrained #-}
+
+projectConfigPreferOldest :: Lens' ProjectConfigShared (Flag PreferOldest)
+projectConfigPreferOldest f s = fmap (\x -> s{T.projectConfigPreferOldest = x}) (f (T.projectConfigPreferOldest s))
+{-# INLINEABLE projectConfigPreferOldest #-}
+
+projectConfigProgPathExtra :: Lens' ProjectConfigShared (NubList FilePath)
+projectConfigProgPathExtra f s = fmap (\x -> s{T.projectConfigProgPathExtra = x}) (f (T.projectConfigProgPathExtra s))
+{-# INLINEABLE projectConfigProgPathExtra #-}
+
+projectConfigMultiRepl :: Lens' ProjectConfigShared (Flag Bool)
+projectConfigMultiRepl f s = fmap (\x -> s{T.projectConfigMultiRepl = x}) (f (T.projectConfigMultiRepl s))
+{-# INLINEABLE projectConfigMultiRepl #-}
+
+packageConfigProgramPaths :: Lens' PackageConfig (MapLast String FilePath)
+packageConfigProgramPaths f s = fmap (\x -> s{T.packageConfigProgramPaths = x}) (f (T.packageConfigProgramPaths s))
+{-# INLINEABLE packageConfigProgramPaths #-}
+
+packageConfigProgramArgs :: Lens' PackageConfig (MapMappend String [String])
+packageConfigProgramArgs f s = fmap (\x -> s{T.packageConfigProgramArgs = x}) (f (T.packageConfigProgramArgs s))
+{-# INLINEABLE packageConfigProgramArgs #-}
+
+packageConfigProgramPathExtra :: Lens' PackageConfig (NubList FilePath)
+packageConfigProgramPathExtra f s = fmap (\x -> s{T.packageConfigProgramPathExtra = x}) (f (T.packageConfigProgramPathExtra s))
+{-# INLINEABLE packageConfigProgramPathExtra #-}
+
+packageConfigFlagAssignment :: Lens' PackageConfig (FlagAssignment)
+packageConfigFlagAssignment f s = fmap (\x -> s{T.packageConfigFlagAssignment = x}) (f (T.packageConfigFlagAssignment s))
+{-# INLINEABLE packageConfigFlagAssignment #-}
+
+packageConfigVanillaLib :: Lens' PackageConfig (Flag Bool)
+packageConfigVanillaLib f s = fmap (\x -> s{T.packageConfigVanillaLib = x}) (f (T.packageConfigVanillaLib s))
+{-# INLINEABLE packageConfigVanillaLib #-}
+
+packageConfigSharedLib :: Lens' PackageConfig (Flag Bool)
+packageConfigSharedLib f s = fmap (\x -> s{T.packageConfigSharedLib = x}) (f (T.packageConfigSharedLib s))
+{-# INLINEABLE packageConfigSharedLib #-}
+
+packageConfigStaticLib :: Lens' PackageConfig (Flag Bool)
+packageConfigStaticLib f s = fmap (\x -> s{T.packageConfigStaticLib = x}) (f (T.packageConfigStaticLib s))
+{-# INLINEABLE packageConfigStaticLib #-}
+
+packageConfigDynExe :: Lens' PackageConfig (Flag Bool)
+packageConfigDynExe f s = fmap (\x -> s{T.packageConfigDynExe = x}) (f (T.packageConfigDynExe s))
+{-# INLINEABLE packageConfigDynExe #-}
+
+packageConfigFullyStaticExe :: Lens' PackageConfig (Flag Bool)
+packageConfigFullyStaticExe f s = fmap (\x -> s{T.packageConfigFullyStaticExe = x}) (f (T.packageConfigFullyStaticExe s))
+{-# INLINEABLE packageConfigFullyStaticExe #-}
+
+packageConfigProf :: Lens' PackageConfig (Flag Bool)
+packageConfigProf f s = fmap (\x -> s{T.packageConfigProf = x}) (f (T.packageConfigProf s))
+{-# INLINEABLE packageConfigProf #-}
+
+packageConfigProfLib :: Lens' PackageConfig (Flag Bool)
+packageConfigProfLib f s = fmap (\x -> s{T.packageConfigProfLib = x}) (f (T.packageConfigProfLib s))
+{-# INLINEABLE packageConfigProfLib #-}
+
+packageConfigProfShared :: Lens' PackageConfig (Flag Bool)
+packageConfigProfShared f s = fmap (\x -> s{T.packageConfigProfShared = x}) (f (T.packageConfigProfShared s))
+{-# INLINEABLE packageConfigProfShared #-}
+
+packageConfigProfExe :: Lens' PackageConfig (Flag Bool)
+packageConfigProfExe f s = fmap (\x -> s{T.packageConfigProfExe = x}) (f (T.packageConfigProfExe s))
+{-# INLINEABLE packageConfigProfExe #-}
+
+packageConfigProfDetail :: Lens' PackageConfig (Flag ProfDetailLevel)
+packageConfigProfDetail f s = fmap (\x -> s{T.packageConfigProfDetail = x}) (f (T.packageConfigProfDetail s))
+{-# INLINEABLE packageConfigProfDetail #-}
+
+packageConfigProfLibDetail :: Lens' PackageConfig (Flag ProfDetailLevel)
+packageConfigProfLibDetail f s = fmap (\x -> s{T.packageConfigProfLibDetail = x}) (f (T.packageConfigProfLibDetail s))
+{-# INLINEABLE packageConfigProfLibDetail #-}
+
+packageConfigConfigureArgs :: Lens' PackageConfig [String]
+packageConfigConfigureArgs f s = fmap (\x -> s{T.packageConfigConfigureArgs = x}) (f (T.packageConfigConfigureArgs s))
+{-# INLINEABLE packageConfigConfigureArgs #-}
+
+packageConfigOptimization :: Lens' PackageConfig (Flag OptimisationLevel)
+packageConfigOptimization f s = fmap (\x -> s{T.packageConfigOptimization = x}) (f (T.packageConfigOptimization s))
+{-# INLINEABLE packageConfigOptimization #-}
+
+packageConfigProgPrefix :: Lens' PackageConfig (Flag PathTemplate)
+packageConfigProgPrefix f s = fmap (\x -> s{T.packageConfigProgPrefix = x}) (f (T.packageConfigProgPrefix s))
+{-# INLINEABLE packageConfigProgPrefix #-}
+
+packageConfigProgSuffix :: Lens' PackageConfig (Flag PathTemplate)
+packageConfigProgSuffix f s = fmap (\x -> s{T.packageConfigProgSuffix = x}) (f (T.packageConfigProgSuffix s))
+{-# INLINEABLE packageConfigProgSuffix #-}
+
+packageConfigExtraLibDirs :: Lens' PackageConfig [FilePath]
+packageConfigExtraLibDirs f s = fmap (\x -> s{T.packageConfigExtraLibDirs = x}) (f (T.packageConfigExtraLibDirs s))
+{-# INLINEABLE packageConfigExtraLibDirs #-}
+
+packageConfigExtraLibDirsStatic :: Lens' PackageConfig [FilePath]
+packageConfigExtraLibDirsStatic f s = fmap (\x -> s{T.packageConfigExtraLibDirsStatic = x}) (f (T.packageConfigExtraLibDirsStatic s))
+{-# INLINEABLE packageConfigExtraLibDirsStatic #-}
+
+packageConfigExtraFrameworkDirs :: Lens' PackageConfig [FilePath]
+packageConfigExtraFrameworkDirs f s = fmap (\x -> s{T.packageConfigExtraFrameworkDirs = x}) (f (T.packageConfigExtraFrameworkDirs s))
+{-# INLINEABLE packageConfigExtraFrameworkDirs #-}
+
+packageConfigExtraIncludeDirs :: Lens' PackageConfig [FilePath]
+packageConfigExtraIncludeDirs f s = fmap (\x -> s{T.packageConfigExtraIncludeDirs = x}) (f (T.packageConfigExtraIncludeDirs s))
+{-# INLINEABLE packageConfigExtraIncludeDirs #-}
+
+packageConfigGHCiLib :: Lens' PackageConfig (Flag Bool)
+packageConfigGHCiLib f s = fmap (\x -> s{T.packageConfigGHCiLib = x}) (f (T.packageConfigGHCiLib s))
+{-# INLINEABLE packageConfigGHCiLib #-}
+
+packageConfigSplitSections :: Lens' PackageConfig (Flag Bool)
+packageConfigSplitSections f s = fmap (\x -> s{T.packageConfigSplitSections = x}) (f (T.packageConfigSplitSections s))
+{-# INLINEABLE packageConfigSplitSections #-}
+
+packageConfigSplitObjs :: Lens' PackageConfig (Flag Bool)
+packageConfigSplitObjs f s = fmap (\x -> s{T.packageConfigSplitObjs = x}) (f (T.packageConfigSplitObjs s))
+{-# INLINEABLE packageConfigSplitObjs #-}
+
+packageConfigStripExes :: Lens' PackageConfig (Flag Bool)
+packageConfigStripExes f s = fmap (\x -> s{T.packageConfigStripExes = x}) (f (T.packageConfigStripExes s))
+{-# INLINEABLE packageConfigStripExes #-}
+
+packageConfigStripLibs :: Lens' PackageConfig (Flag Bool)
+packageConfigStripLibs f s = fmap (\x -> s{T.packageConfigStripLibs = x}) (f (T.packageConfigStripLibs s))
+{-# INLINEABLE packageConfigStripLibs #-}
+
+packageConfigTests :: Lens' PackageConfig (Flag Bool)
+packageConfigTests f s = fmap (\x -> s{T.packageConfigTests = x}) (f (T.packageConfigTests s))
+{-# INLINEABLE packageConfigTests #-}
+
+packageConfigBenchmarks :: Lens' PackageConfig (Flag Bool)
+packageConfigBenchmarks f s = fmap (\x -> s{T.packageConfigBenchmarks = x}) (f (T.packageConfigBenchmarks s))
+{-# INLINEABLE packageConfigBenchmarks #-}
+
+packageConfigCoverage :: Lens' PackageConfig (Flag Bool)
+packageConfigCoverage f s = fmap (\x -> s{T.packageConfigCoverage = x}) (f (T.packageConfigCoverage s))
+{-# INLINEABLE packageConfigCoverage #-}
+
+packageConfigRelocatable :: Lens' PackageConfig (Flag Bool)
+packageConfigRelocatable f s = fmap (\x -> s{T.packageConfigRelocatable = x}) (f (T.packageConfigRelocatable s))
+{-# INLINEABLE packageConfigRelocatable #-}
+
+packageConfigDebugInfo :: Lens' PackageConfig (Flag DebugInfoLevel)
+packageConfigDebugInfo f s = fmap (\x -> s{T.packageConfigDebugInfo = x}) (f (T.packageConfigDebugInfo s))
+{-# INLINEABLE packageConfigDebugInfo #-}
+
+packageConfigDumpBuildInfo :: Lens' PackageConfig (Flag DumpBuildInfo)
+packageConfigDumpBuildInfo f s = fmap (\x -> s{T.packageConfigDumpBuildInfo = x}) (f (T.packageConfigDumpBuildInfo s))
+{-# INLINEABLE packageConfigDumpBuildInfo #-}
+
+packageConfigRunTests :: Lens' PackageConfig (Flag Bool)
+packageConfigRunTests f s = fmap (\x -> s{T.packageConfigRunTests = x}) (f (T.packageConfigRunTests s))
+{-# INLINEABLE packageConfigRunTests #-}
+
+packageConfigDocumentation :: Lens' PackageConfig (Flag Bool)
+packageConfigDocumentation f s = fmap (\x -> s{T.packageConfigDocumentation = x}) (f (T.packageConfigDocumentation s))
+{-# INLINEABLE packageConfigDocumentation #-}
+
+packageConfigHaddockHoogle :: Lens' PackageConfig (Flag Bool)
+packageConfigHaddockHoogle f s = fmap (\x -> s{T.packageConfigHaddockHoogle = x}) (f (T.packageConfigHaddockHoogle s))
+{-# INLINEABLE packageConfigHaddockHoogle #-}
+
+packageConfigHaddockHtml :: Lens' PackageConfig (Flag Bool)
+packageConfigHaddockHtml f s = fmap (\x -> s{T.packageConfigHaddockHtml = x}) (f (T.packageConfigHaddockHtml s))
+{-# INLINEABLE packageConfigHaddockHtml #-}
+
+packageConfigHaddockHtmlLocation :: Lens' PackageConfig (Flag String)
+packageConfigHaddockHtmlLocation f s = fmap (\x -> s{T.packageConfigHaddockHtmlLocation = x}) (f (T.packageConfigHaddockHtmlLocation s))
+{-# INLINEABLE packageConfigHaddockHtmlLocation #-}
+
+packageConfigHaddockForeignLibs :: Lens' PackageConfig (Flag Bool)
+packageConfigHaddockForeignLibs f s = fmap (\x -> s{T.packageConfigHaddockForeignLibs = x}) (f (T.packageConfigHaddockForeignLibs s))
+{-# INLINEABLE packageConfigHaddockForeignLibs #-}
+
+packageConfigHaddockExecutables :: Lens' PackageConfig (Flag Bool)
+packageConfigHaddockExecutables f s = fmap (\x -> s{T.packageConfigHaddockExecutables = x}) (f (T.packageConfigHaddockExecutables s))
+{-# INLINEABLE packageConfigHaddockExecutables #-}
+
+packageConfigHaddockTestSuites :: Lens' PackageConfig (Flag Bool)
+packageConfigHaddockTestSuites f s = fmap (\x -> s{T.packageConfigHaddockTestSuites = x}) (f (T.packageConfigHaddockTestSuites s))
+{-# INLINEABLE packageConfigHaddockTestSuites #-}
+
+packageConfigHaddockBenchmarks :: Lens' PackageConfig (Flag Bool)
+packageConfigHaddockBenchmarks f s = fmap (\x -> s{T.packageConfigHaddockBenchmarks = x}) (f (T.packageConfigHaddockBenchmarks s))
+{-# INLINEABLE packageConfigHaddockBenchmarks #-}
+
+packageConfigHaddockInternal :: Lens' PackageConfig (Flag Bool)
+packageConfigHaddockInternal f s = fmap (\x -> s{T.packageConfigHaddockInternal = x}) (f (T.packageConfigHaddockInternal s))
+{-# INLINEABLE packageConfigHaddockInternal #-}
+
+packageConfigHaddockCss :: Lens' PackageConfig (Flag FilePath)
+packageConfigHaddockCss f s = fmap (\x -> s{T.packageConfigHaddockCss = x}) (f (T.packageConfigHaddockCss s))
+{-# INLINEABLE packageConfigHaddockCss #-}
+
+packageConfigHaddockLinkedSource :: Lens' PackageConfig (Flag Bool)
+packageConfigHaddockLinkedSource f s = fmap (\x -> s{T.packageConfigHaddockLinkedSource = x}) (f (T.packageConfigHaddockLinkedSource s))
+{-# INLINEABLE packageConfigHaddockLinkedSource #-}
+
+packageConfigHaddockQuickJump :: Lens' PackageConfig (Flag Bool)
+packageConfigHaddockQuickJump f s = fmap (\x -> s{T.packageConfigHaddockQuickJump = x}) (f (T.packageConfigHaddockQuickJump s))
+{-# INLINEABLE packageConfigHaddockQuickJump #-}
+
+packageConfigHaddockHscolourCss :: Lens' PackageConfig (Flag FilePath)
+packageConfigHaddockHscolourCss f s = fmap (\x -> s{T.packageConfigHaddockHscolourCss = x}) (f (T.packageConfigHaddockHscolourCss s))
+{-# INLINEABLE packageConfigHaddockHscolourCss #-}
+
+packageConfigHaddockContents :: Lens' PackageConfig (Flag PathTemplate)
+packageConfigHaddockContents f s = fmap (\x -> s{T.packageConfigHaddockContents = x}) (f (T.packageConfigHaddockContents s))
+{-# INLINEABLE packageConfigHaddockContents #-}
+
+packageConfigHaddockIndex :: Lens' PackageConfig (Flag PathTemplate)
+packageConfigHaddockIndex f s = fmap (\x -> s{T.packageConfigHaddockIndex = x}) (f (T.packageConfigHaddockIndex s))
+{-# INLINEABLE packageConfigHaddockIndex #-}
+
+packageConfigHaddockBaseUrl :: Lens' PackageConfig (Flag String)
+packageConfigHaddockBaseUrl f s = fmap (\x -> s{T.packageConfigHaddockBaseUrl = x}) (f (T.packageConfigHaddockBaseUrl s))
+{-# INLINEABLE packageConfigHaddockBaseUrl #-}
+
+packageConfigHaddockResourcesDir :: Lens' PackageConfig (Flag String)
+packageConfigHaddockResourcesDir f s = fmap (\x -> s{T.packageConfigHaddockResourcesDir = x}) (f (T.packageConfigHaddockResourcesDir s))
+{-# INLINEABLE packageConfigHaddockResourcesDir #-}
+
+packageConfigHaddockOutputDir :: Lens' PackageConfig (Flag FilePath)
+packageConfigHaddockOutputDir f s = fmap (\x -> s{T.packageConfigHaddockOutputDir = x}) (f (T.packageConfigHaddockOutputDir s))
+{-# INLINEABLE packageConfigHaddockOutputDir #-}
+
+packageConfigHaddockUseUnicode :: Lens' PackageConfig (Flag Bool)
+packageConfigHaddockUseUnicode f s = fmap (\x -> s{T.packageConfigHaddockUseUnicode = x}) (f (T.packageConfigHaddockUseUnicode s))
+{-# INLINEABLE packageConfigHaddockUseUnicode #-}
+
+packageConfigHaddockForHackage :: Lens' PackageConfig (Flag HaddockTarget)
+packageConfigHaddockForHackage f s = fmap (\x -> s{T.packageConfigHaddockForHackage = x}) (f (T.packageConfigHaddockForHackage s))
+{-# INLINEABLE packageConfigHaddockForHackage #-}
+
+packageConfigTestHumanLog :: Lens' PackageConfig (Flag PathTemplate)
+packageConfigTestHumanLog f s = fmap (\x -> s{T.packageConfigTestHumanLog = x}) (f (T.packageConfigTestHumanLog s))
+{-# INLINEABLE packageConfigTestHumanLog #-}
+
+packageConfigTestMachineLog :: Lens' PackageConfig (Flag PathTemplate)
+packageConfigTestMachineLog f s = fmap (\x -> s{T.packageConfigTestMachineLog = x}) (f (T.packageConfigTestMachineLog s))
+{-# INLINEABLE packageConfigTestMachineLog #-}
+
+packageConfigTestShowDetails :: Lens' PackageConfig (Flag TestShowDetails)
+packageConfigTestShowDetails f s = fmap (\x -> s{T.packageConfigTestShowDetails = x}) (f (T.packageConfigTestShowDetails s))
+{-# INLINEABLE packageConfigTestShowDetails #-}
+
+packageConfigTestKeepTix :: Lens' PackageConfig (Flag Bool)
+packageConfigTestKeepTix f s = fmap (\x -> s{T.packageConfigTestKeepTix = x}) (f (T.packageConfigTestKeepTix s))
+{-# INLINEABLE packageConfigTestKeepTix #-}
+
+packageConfigTestWrapper :: Lens' PackageConfig (Flag FilePath)
+packageConfigTestWrapper f s = fmap (\x -> s{T.packageConfigTestWrapper = x}) (f (T.packageConfigTestWrapper s))
+{-# INLINEABLE packageConfigTestWrapper #-}
+
+packageConfigTestFailWhenNoTestSuites :: Lens' PackageConfig (Flag Bool)
+packageConfigTestFailWhenNoTestSuites f s = fmap (\x -> s{T.packageConfigTestFailWhenNoTestSuites = x}) (f (T.packageConfigTestFailWhenNoTestSuites s))
+{-# INLINEABLE packageConfigTestFailWhenNoTestSuites #-}
+
+packageConfigTestTestOptions :: Lens' PackageConfig [PathTemplate]
+packageConfigTestTestOptions f s = fmap (\x -> s{T.packageConfigTestTestOptions = x}) (f (T.packageConfigTestTestOptions s))
+{-# INLINEABLE packageConfigTestTestOptions #-}
+
+packageConfigBenchmarkOptions :: Lens' PackageConfig [PathTemplate]
+packageConfigBenchmarkOptions f s = fmap (\x -> s{T.packageConfigBenchmarkOptions = x}) (f (T.packageConfigBenchmarkOptions s))
+{-# INLINEABLE packageConfigBenchmarkOptions #-}
diff --git a/cabal-install/src/Distribution/Client/ProjectConfig/Parsec.hs b/cabal-install/src/Distribution/Client/ProjectConfig/Parsec.hs
new file mode 100644
index 00000000000..f4d638c0d6b
--- /dev/null
+++ b/cabal-install/src/Distribution/Client/ProjectConfig/Parsec.hs
@@ -0,0 +1,427 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+-- | Parsing project configuration.
+module Distribution.Client.ProjectConfig.Parsec
+  ( -- * Package configuration
+    parseProjectSkeleton
+  , parseProject
+  , ProjectConfigSkeleton
+  , ProjectConfig (..)
+
+    -- ** Parsing
+  , ParseResult
+  , runParseResult
+  ) where
+
+import Distribution.CabalSpecVersion
+import Distribution.Client.HttpUtils
+import Distribution.Client.ProjectConfig.FieldGrammar (packageConfigFieldGrammar, projectConfigFieldGrammar)
+import Distribution.Client.ProjectConfig.Legacy (ProjectConfigSkeleton)
+import qualified Distribution.Client.ProjectConfig.Lens as L
+import Distribution.Client.ProjectConfig.Types
+import Distribution.Client.Types.Repo hiding (repoName)
+import Distribution.Client.Types.RepoName (RepoName (..))
+import Distribution.Client.Types.SourceRepo (sourceRepositoryPackageGrammar)
+import Distribution.Client.Utils.Parsec
+import Distribution.Compat.Lens
+import Distribution.Compat.Prelude
+import Distribution.FieldGrammar
+import Distribution.FieldGrammar.Parsec (NamelessField (..), namelessFieldAnn)
+import Distribution.Fields (Field (..), FieldLine (..), FieldName, Name (..), SectionArg (..), readFields')
+import Distribution.Fields.ConfVar (parseConditionConfVar)
+import Distribution.Fields.Field (fieldLinesToString, sectionArgAnn)
+import Distribution.Fields.LexerMonad (toPWarnings)
+import Distribution.Fields.ParseResult
+import Distribution.Parsec (ParsecParser, eitherParsec, parsec, parsecFilePath, runParsecParser)
+import Distribution.Parsec.FieldLineStream (fieldLineStreamFromBS)
+import Distribution.Parsec.Position (Position (..), incPos, zeroPos)
+import Distribution.Parsec.Warning (PWarnType (..))
+import Distribution.Simple.Program.Db (ProgramDb, defaultProgramDb, knownPrograms, lookupKnownProgram)
+import Distribution.Simple.Program.Types (programName)
+import Distribution.Simple.Setup
+import Distribution.Simple.Utils (debug, noticeDoc)
+import Distribution.Solver.Types.ProjectConfigPath
+import Distribution.System (buildOS)
+import Distribution.Types.CondTree (CondBranch (..), CondTree (..))
+import Distribution.Types.ConfVar (ConfVar (..))
+import Distribution.Types.PackageName (PackageName)
+import Distribution.Utils.Generic (fromUTF8BS, toUTF8BS, validateUTF8)
+import Distribution.Utils.NubList (toNubList)
+import Distribution.Utils.String (trim)
+import Distribution.Verbosity
+
+import Control.Monad.State.Strict (StateT, execStateT, lift)
+import qualified Data.ByteString as BS
+import Data.Coerce (coerce)
+import qualified Data.Map.Strict as Map
+import qualified Data.Set as Set
+import Distribution.Client.Errors.Parser (ProjectFileSource (..))
+import qualified Distribution.Compat.CharParsing as P
+import Network.URI (parseURI, uriFragment, uriPath, uriScheme)
+import System.Directory (createDirectoryIfMissing, makeAbsolute)
+import System.FilePath (isAbsolute, isPathSeparator, makeValid, splitFileName, (</>))
+import qualified Text.Parsec
+import Text.PrettyPrint (render)
+import qualified Text.PrettyPrint as Disp
+
+singletonProjectConfigSkeleton :: ProjectConfig -> ProjectConfigSkeleton
+singletonProjectConfigSkeleton x = CondNode x mempty mempty
+
+readPreprocessFields :: BS.ByteString -> ParseResult src [Field Position]
+readPreprocessFields bs = do
+  case readFields' bs' of
+    Right (fs, lexWarnings) -> do
+      parseWarnings (toPWarnings lexWarnings)
+      for_ invalidUtf8 $ \pos ->
+        parseWarning zeroPos PWTUTF $ "UTF8 encoding problem at byte offset " ++ show pos
+      return fs
+    Left perr -> parseFatalFailure pos (show perr)
+      where
+        ppos = Text.Parsec.errorPos perr
+        pos = Position (Text.Parsec.sourceLine ppos) (Text.Parsec.sourceColumn ppos)
+  where
+    invalidUtf8 = validateUTF8 bs
+    bs' = case invalidUtf8 of
+      Nothing -> bs
+      Just _ -> toUTF8BS (fromUTF8BS bs)
+
+-- | Parses a project from its root config file, typically cabal.project.
+parseProject
+  :: FilePath
+  -- ^ The root of the project configuration, typically cabal.project
+  -> FilePath
+  -> HttpTransport
+  -> Verbosity
+  -> ProjectConfigToParse
+  -- ^ The contents of the file to parse
+  -> IO (ParseResult ProjectFileSource ProjectConfigSkeleton)
+parseProject rootPath cacheDir httpTransport verbosity configToParse = do
+  let (dir, projectFileName) = splitFileName rootPath
+  projectDir <- makeAbsolute dir
+  projectPath <- canonicalizeConfigPath projectDir (ProjectConfigPath $ projectFileName :| [])
+  parseProjectSkeleton cacheDir httpTransport verbosity projectDir projectPath configToParse
+
+parseProjectSkeleton
+  :: FilePath
+  -> HttpTransport
+  -> Verbosity
+  -> FilePath
+  -- ^ The directory of the project configuration, typically the directory of cabal.project
+  -> ProjectConfigPath
+  -- ^ The path of the file being parsed, either the root or an import
+  -> ProjectConfigToParse
+  -- ^ The contents of the file to parse
+  -> IO (ParseResult ProjectFileSource ProjectConfigSkeleton)
+parseProjectSkeleton cacheDir httpTransport verbosity projectDir source (ProjectConfigToParse bs) = do
+  normSource <- canonicalizeConfigPath projectDir source
+  res <- (sanityWalkPCS False =<<) <$> liftParseResult (go []) (readPreprocessFields bs)
+  pure $ withSource (ProjectFileSource (normSource, bs)) res
+  where
+    go :: [Field Position] -> [Field Position] -> IO (ParseResult ProjectFileSource ProjectConfigSkeleton)
+    go acc (x : xs) = case x of
+      (Field (Name pos name) importLines) | name == "import" -> do
+        liftParseResult
+          ( \importLoc -> do
+              let importLocPath = importLoc `consProjectConfigPath` source
+
+              -- Once we canonicalize the import path, we can check for cyclical imports
+              normSource <- canonicalizeConfigPath projectDir source
+              normLocPath <- canonicalizeConfigPath projectDir importLocPath
+              debug verbosity $ "\nimport path, normalized\n=======================\n" ++ render (docProjectConfigPath normLocPath)
+
+              if isCyclicConfigPath normLocPath
+                then pure $ parseFatalFailure pos (render $ cyclicalImportMsg normLocPath)
+                else do
+                  when
+                    (isUntrimmedUriConfigPath importLocPath)
+                    (noticeDoc verbosity $ untrimmedUriImportMsg (Disp.text "Warning:") importLocPath)
+                  let fs = (\z -> CondNode z [normLocPath] mempty) <$> fieldsToConfig normSource (reverse acc)
+                  importParseResult <- parseProjectSkeleton cacheDir httpTransport verbosity projectDir importLocPath . ProjectConfigToParse =<< fetchImportConfig normLocPath
+
+                  rest <- go [] xs
+                  pure . fmap mconcat . sequence $ [fs, importParseResult, rest]
+          )
+          (parseImport pos importLines)
+      (Section (Name pos "if") args xs') -> do
+        subpcs <- go [] xs'
+        let fs = fmap singletonProjectConfigSkeleton $ fieldsToConfig source (reverse acc)
+        (elseClauses, rest) <- parseElseClauses xs
+        let condNode =
+              (\c pcs e -> CondNode mempty mempty [CondBranch c pcs e])
+                <$> parseConditionConfVar (startOfSection (incPos 2 pos) args) args
+                <*> subpcs
+                <*> elseClauses
+        pure . fmap mconcat . sequence $ [fs, condNode, rest]
+      _ -> go (x : acc) xs
+    go acc [] = do
+      normSource <- canonicalizeConfigPath projectDir source
+      pure . fmap singletonProjectConfigSkeleton . fieldsToConfig normSource $ reverse acc
+
+    parseElseClauses :: [Field Position] -> IO (ParseResult ProjectFileSource (Maybe ProjectConfigSkeleton), ParseResult ProjectFileSource ProjectConfigSkeleton)
+    parseElseClauses x = case x of
+      (Section (Name _pos "else") _args xs' : xs) -> do
+        subpcs <- go [] xs'
+        rest <- go [] xs
+        pure (Just <$> subpcs, rest)
+      (Section (Name pos "elif") args xs' : xs) -> do
+        subpcs <- go [] xs'
+        (elseClauses, rest) <- parseElseClauses xs
+        let condNode =
+              (\c pcs e -> CondNode mempty mempty [CondBranch c pcs e])
+                <$> parseConditionConfVar (startOfSection (incPos 4 pos) args) args
+                <*> subpcs
+                <*> elseClauses
+        pure (Just <$> condNode, rest)
+      _ -> (\r -> (pure Nothing, r)) <$> go [] x
+
+    parseImport :: Position -> [FieldLine Position] -> ParseResult ProjectFileSource FilePath
+    parseImport pos lines' = runFieldParser pos (P.many P.anyChar) cabalSpec lines'
+
+    -- We want a normalized path for @fieldsToConfig@. This eventually surfaces
+    -- in solver rejection messages and build messages "this build was affected
+    -- by the following (project) config files" so we want all paths shown there
+    -- to be relative to the directory of the project, not relative to the file
+    -- they were imported from.
+    fieldsToConfig :: ProjectConfigPath -> [Field Position] -> ParseResult ProjectFileSource ProjectConfig
+    fieldsToConfig sourceConfigPath xs = do
+      let (fs, sectionGroups) = partitionFields xs
+          sections = concat sectionGroups
+      config <- parseFieldGrammarCheckingStanzas cabalSpec fs (projectConfigFieldGrammar sourceConfigPath (knownProgramNames programDb)) stanzas
+      config' <- view stateConfig <$> execStateT (goSections programDb sections) (SectionS config)
+      return config'
+
+    fetchImportConfig :: ProjectConfigPath -> IO BS.ByteString
+    fetchImportConfig (ProjectConfigPath (pci :| _)) = do
+      debug verbosity $ "fetching import: " ++ pci
+      fetch pci
+
+    fetch :: FilePath -> IO BS.ByteString
+    fetch pci = case parseURI (trim pci) of
+      Just uri -> do
+        let fp = cacheDir </> map (\x -> if isPathSeparator x then '_' else x) (makeValid $ show uri)
+        createDirectoryIfMissing True cacheDir
+        _ <- downloadURI httpTransport verbosity uri fp
+        BS.readFile fp
+      Nothing ->
+        BS.readFile $
+          if isAbsolute pci then pci else coerce projectDir </> pci
+
+    modifiesCompiler :: ProjectConfig -> Bool
+    modifiesCompiler pc = isSet projectConfigHcFlavor || isSet projectConfigHcPath || isSet projectConfigHcPkg
+      where
+        isSet f = f (projectConfigShared pc) /= NoFlag
+
+    sanityWalkPCS :: Bool -> ProjectConfigSkeleton -> ParseResult ProjectFileSource ProjectConfigSkeleton
+    sanityWalkPCS underConditional t@(CondNode d _c comps)
+      | underConditional && modifiesCompiler d = parseFatalFailure zeroPos "Cannot set compiler in a conditional clause of a cabal project file"
+      | otherwise = mapM_ sanityWalkBranch comps >> pure t
+
+    sanityWalkBranch :: CondBranch ConfVar [ProjectConfigPath] ProjectConfig -> ParseResult ProjectFileSource ()
+    sanityWalkBranch (CondBranch _c t f) = traverse_ (sanityWalkPCS True) f >> sanityWalkPCS True t >> pure ()
+
+    programDb = defaultProgramDb
+
+startOfSection :: Position -> [SectionArg Position] -> Position
+-- The case where we have no args is the start of the section
+startOfSection defaultPos [] = defaultPos
+-- Otherwise the start of the section is the position of the first argument.
+startOfSection _ (cond : _) = sectionArgAnn cond
+
+knownProgramNames :: ProgramDb -> [String]
+knownProgramNames programDb = (programName . fst) <$> knownPrograms programDb
+
+-- | Monad in which sections are parsed
+type SectionParser src = StateT SectionS (ParseResult src)
+
+-- | State of 'SectionParser'
+newtype SectionS = SectionS
+  { _stateConfig :: ProjectConfig
+  }
+
+stateConfig :: Lens' SectionS ProjectConfig
+stateConfig f (SectionS cfg) = SectionS <$> f cfg
+{-# INLINEABLE stateConfig #-}
+
+goSections :: ProgramDb -> [Section Position] -> SectionParser src ()
+goSections programDb = traverse_ (parseSection programDb)
+
+parseSection :: ProgramDb -> Section Position -> SectionParser src ()
+parseSection programDb (MkSection (Name pos name) args secFields)
+  | name == "source-repository-package" = do
+      verifyNullSubsections
+      verifyNullSectionArgs
+      srp <- lift $ parseFieldGrammar cabalSpec fields sourceRepositoryPackageGrammar
+      stateConfig . L.projectPackagesRepo %= (<> [srp])
+  | name == "program-options" = do
+      verifyNullSubsections
+      verifyNullSectionArgs
+      opts' <- lift $ parseProgramArgs programDb fields
+      stateConfig . L.projectConfigLocalPackages . L.packageConfigProgramArgs %= (opts' <>)
+  | name == "program-locations" = do
+      verifyNullSubsections
+      verifyNullSectionArgs
+      paths' <- lift $ parseProgramPaths programDb fields
+      stateConfig . L.projectConfigLocalPackages . L.packageConfigProgramPaths %= (paths' <>)
+  | name == "repository" = do
+      verifyNullSubsections
+      mRepoName <- lift $ parseRepoName pos args
+      case mRepoName of
+        Just repoName -> do
+          remoteRepo <- lift $ parseFieldGrammar cabalSpec fields (remoteRepoGrammar repoName)
+          remoteOrLocalRepo <- lift $ postProcessRemoteRepo pos remoteRepo
+          case remoteOrLocalRepo of
+            Left local -> stateConfig . L.projectConfigShared . L.projectConfigLocalNoIndexRepos %= (<> toNubList [local])
+            Right remote -> stateConfig . L.projectConfigShared . L.projectConfigRemoteRepos %= (<> toNubList [remote])
+        Nothing -> lift $ parseFailure pos "a 'repository' section requires the repository name as an argument"
+  | name == "package" = do
+      verifyNullSubsections
+      package <- lift $ parsePackageName pos args
+      case package of
+        Just AllPackages -> do
+          packageCfg' <- parsePackageConfig
+          stateConfig . L.projectConfigAllPackages %= (packageCfg' <>)
+        Just (SpecificPackage packageName) -> do
+          packageCfg <- parsePackageConfig
+          stateConfig . L.projectConfigSpecificPackage %= (<> MapMappend (Map.singleton packageName packageCfg))
+        Nothing -> do
+          lift $ parseWarning pos PWTUnknownSection "target package name or * required"
+          return ()
+  | otherwise = do
+      warnInvalidSubsection pos name
+  where
+    (fields, sections) = partitionFields secFields
+    warnInvalidSubsection pos' name' = lift $ parseWarning pos' PWTInvalidSubsection $ "Invalid subsection " ++ show name'
+    programNames = knownProgramNames programDb
+    verifyNullSubsections = unless (null sections) (warnInvalidSubsection pos name)
+    verifyNullSectionArgs = unless (null args) (lift $ parseFailure pos $ "The section '" <> (show name) <> "' takes no arguments")
+    parsePackageConfig = do
+      packageCfg <- lift $ parseFieldGrammar cabalSpec fields (packageConfigFieldGrammar programNames)
+      args' <- lift $ parseProgramArgs programDb fields
+      paths <- lift $ parseProgramPaths programDb fields
+      return packageCfg{packageConfigProgramPaths = paths, packageConfigProgramArgs = args'}
+
+stanzas :: Set BS.ByteString
+stanzas = Set.fromList ["source-repository-package", "program-options", "program-locations", "repository", "package"]
+
+-- | Currently a duplicate of 'Distribution.Client.Config.postProcessRepo' but migrated to Parsec ParseResult.
+postProcessRemoteRepo :: Position -> RemoteRepo -> ParseResult src (Either LocalRepo RemoteRepo)
+postProcessRemoteRepo pos repo = case uriScheme (remoteRepoURI repo) of
+  -- TODO: check that there are no authority, query or fragment
+  -- Note: the trailing colon is important
+  "file+noindex:" -> do
+    let uri = normaliseFileNoIndexURI buildOS $ remoteRepoURI repo
+    return $ Left $ LocalRepo (remoteRepoName repo) (uriPath uri) (uriFragment uri == "#shared-cache")
+  _ -> do
+    when (remoteRepoKeyThreshold repo > length (remoteRepoRootKeys repo)) $
+      warning $
+        "'key-threshold' for repository "
+          ++ show (remoteRepoName repo)
+          ++ " higher than number of keys"
+
+    when (not (null (remoteRepoRootKeys repo)) && remoteRepoSecure repo /= Just True) $
+      warning $
+        "'root-keys' for repository "
+          ++ show (remoteRepoName repo)
+          ++ " non-empty, but 'secure' not set to True."
+
+    return $ Right repo
+    where
+      warning msg = parseWarning pos PWTOther msg
+
+parseRepoName :: Position -> [SectionArg Position] -> ParseResult src (Maybe RepoName)
+parseRepoName pos args = case args of
+  [SecArgName _ secName] -> parseName secName
+  [SecArgStr _ secName] -> parseName secName
+  [SecArgOther _ secName] -> parseName secName
+  _ -> return Nothing
+  where
+    parseName :: BS.ByteString -> ParseResult src (Maybe RepoName)
+    parseName str =
+      let repoNameStr = fromUTF8BS str
+       in case eitherParsec repoNameStr of
+            Left _ -> do
+              parseFailure pos ("Invalid repository name" ++ repoNameStr)
+              return Nothing
+            Right name -> return $ Just name
+
+data PackageConfigTarget = AllPackages | SpecificPackage !PackageName
+
+parsePackageName :: Position -> [SectionArg Position] -> ParseResult src (Maybe PackageConfigTarget)
+parsePackageName pos args = case args of
+  [SecArgName _ secName] -> parseName secName
+  [SecArgStr _ secName] -> parseName secName
+  [SecArgOther _ secName] -> parseName secName
+  _ -> return Nothing
+  where
+    parseName secName = case runParsecParser parser "<parsePackageName>" (fieldLineStreamFromBS secName) of
+      Left _ -> do
+        parseFailure pos ("Invalid package name" ++ fromUTF8BS secName)
+        return Nothing
+      Right cfgTarget -> return $ pure cfgTarget
+    parser :: ParsecParser PackageConfigTarget
+    parser =
+      P.choice [P.try (P.char '*' >> return AllPackages), SpecificPackage <$> parsec]
+
+-- | Parse fields of a program-options stanza.
+parseProgramArgs :: ProgramDb -> Fields Position -> ParseResult src (MapMappend String [String])
+parseProgramArgs programDb fields = foldM parseField mempty (filter hasOptionsSuffix $ Map.toList fields)
+  where
+    parseField programArgs (fieldName, fieldLines) = do
+      case readProgramName "-options" programDb fieldName of
+        Nothing -> warnUnknownFields fieldName fieldLines >> return programArgs
+        Just program -> do
+          args <- parseProgramArgsField $ reverse fieldLines
+          return $ programArgs <> MapMappend (Map.singleton program args)
+    hasOptionsSuffix (fieldName, _) = BS.isSuffixOf "-options" fieldName
+
+-- | Parse fields of a program-locations stanza.
+parseProgramPaths :: ProgramDb -> Fields Position -> ParseResult src (MapLast String FilePath)
+parseProgramPaths programDb fields = foldM parseField mempty (filter hasLocationSuffix $ Map.toList fields)
+  where
+    parseField paths (fieldName, fieldLines) = do
+      case readProgramName "-location" programDb fieldName of
+        Nothing -> warnUnknownFields fieldName fieldLines >> return paths
+        Just program -> do
+          case fieldLines of
+            (MkNamelessField pos lines') : _ -> do
+              fp <- runFieldParser pos parsecFilePath cabalSpec lines'
+              return $ paths <> MapLast (Map.singleton program fp)
+            [] -> return mempty
+    hasLocationSuffix (fieldName, _) = BS.isSuffixOf "-location" fieldName
+
+-- | Parse all arguments to a single program in program-options stanza.
+-- By processing '[NamelessField Position]', we support multiple occurrences of the field, concatenating the arguments.
+parseProgramArgsField :: [NamelessField Position] -> ParseResult src ([String])
+parseProgramArgsField fieldLines =
+  concat <$> mapM (\(MkNamelessField _ lines') -> parseProgramArgsFieldLines lines') fieldLines
+
+-- | Parse all fieldLines of a single field occurrence in a program-options stanza.
+parseProgramArgsFieldLines :: [FieldLine Position] -> ParseResult src [String]
+parseProgramArgsFieldLines lines' = return $ splitArgs strLines
+  where
+    strLines = fieldLinesToString lines'
+
+type FieldSuffix = String
+
+-- | Extract the program name of a <progname> field, allow it to have a suffix such as '-options' and check whether the 'ProgramDB' contains it.
+readProgramName :: FieldSuffix -> ProgramDb -> FieldName -> Maybe String
+readProgramName suffix programDb fieldName =
+  parseProgramName suffix fieldName >>= ((flip lookupKnownProgram) programDb) >>= pure . programName
+
+parseProgramName :: FieldSuffix -> FieldName -> Maybe String
+parseProgramName suffix fieldName = case runParsecParser parser "<parseProgramName>" fieldNameStream of
+  Left _ -> Nothing
+  Right str -> Just str
+  where
+    parser = P.manyTill P.anyChar (P.try ((P.string suffix)) <* P.eof)
+    fieldNameStream = fieldLineStreamFromBS fieldName
+
+-- | Issue a 'PWTUnknownField' warning at all occurrences of a field.
+warnUnknownFields :: FieldName -> [NamelessField Position] -> ParseResult src ()
+warnUnknownFields fieldName fieldLines = for_ fieldLines (\field -> parseWarning (pos field) PWTUnknownField message)
+  where
+    message = "Unknown field: " ++ show fieldName
+    pos = namelessFieldAnn
+
+cabalSpec :: CabalSpecVersion
+cabalSpec = cabalSpecLatest
diff --git a/cabal-install/src/Distribution/Client/ProjectConfig/Types.hs b/cabal-install/src/Distribution/Client/ProjectConfig/Types.hs
index 1a2b6ae2fa6..220834a331c 100644
--- a/cabal-install/src/Distribution/Client/ProjectConfig/Types.hs
+++ b/cabal-install/src/Distribution/Client/ProjectConfig/Types.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE DeriveGeneric #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
 
@@ -10,6 +11,8 @@ module Distribution.Client.ProjectConfig.Types
   , ProjectConfigShared (..)
   , ProjectConfigProvenance (..)
   , PackageConfig (..)
+  , ProjectFileParser (..)
+  , defaultProjectFileParser
 
     -- * Resolving configuration
   , SolverSettings (..)
@@ -168,6 +171,7 @@ data ProjectConfigBuildOnly = ProjectConfigBuildOnly
   , projectConfigReportPlanningFailure :: Flag Bool
   , projectConfigSymlinkBinDir :: Flag FilePath
   , projectConfigNumJobs :: Flag (Maybe Int)
+  -- ^ Use 'Just n' for number of jobs, 'Nothing' for number of jobs equal to the number of CPUs and 'NoFlag' if flag is not given.
   , projectConfigUseSemaphore :: Flag Bool
   , projectConfigKeepGoing :: Flag Bool
   , projectConfigOfflineMode :: Flag Bool
@@ -187,6 +191,7 @@ data ProjectConfigShared = ProjectConfigShared
   , projectConfigConfigFile :: Flag FilePath
   , projectConfigProjectDir :: Flag FilePath
   , projectConfigProjectFile :: Flag FilePath
+  , projectConfigProjectFileParser :: Flag ProjectFileParser
   , projectConfigIgnoreProject :: Flag Bool
   , projectConfigHcFlavor :: Flag CompilerFlavor
   , projectConfigHcPath :: Flag FilePath
@@ -237,6 +242,20 @@ data ProjectConfigShared = ProjectConfigShared
   }
   deriving (Eq, Show, Generic)
 
+data ProjectFileParser
+  = LegacyParser
+  | ParsecParser
+  | FallbackParser
+  | CompareParser
+  deriving (Eq, Show, Generic)
+
+defaultProjectFileParser :: ProjectFileParser
+#ifdef LEGACY_COMPARISON
+defaultProjectFileParser = CompareParser
+#else
+defaultProjectFileParser = FallbackParser
+#endif
+
 -- | Specifies the provenance of project configuration, whether defaults were
 -- used or if the configuration was read from an explicit file path.
 data ProjectConfigProvenance
@@ -327,12 +346,14 @@ instance Binary ProjectConfigBuildOnly
 instance Binary ProjectConfigShared
 instance Binary ProjectConfigProvenance
 instance Binary PackageConfig
+instance Binary ProjectFileParser
 
 instance Structured ProjectConfig
 instance Structured ProjectConfigBuildOnly
 instance Structured ProjectConfigShared
 instance Structured ProjectConfigProvenance
 instance Structured PackageConfig
+instance Structured ProjectFileParser
 
 -- | Newtype wrapper for 'Map' that provides a 'Monoid' instance that takes
 -- the last value rather than the first value for overlapping keys.
diff --git a/cabal-install/src/Distribution/Client/ProjectFlags.hs b/cabal-install/src/Distribution/Client/ProjectFlags.hs
index 29b964bb99b..9060f3b863b 100644
--- a/cabal-install/src/Distribution/Client/ProjectFlags.hs
+++ b/cabal-install/src/Distribution/Client/ProjectFlags.hs
@@ -10,9 +10,10 @@ module Distribution.Client.ProjectFlags
   ) where
 
 import Distribution.Client.Compat.Prelude
+import Distribution.Client.ProjectConfig.Types (ProjectFileParser (..), defaultProjectFileParser)
 import Prelude ()
 
-import Distribution.ReadE (succeedReadE)
+import Distribution.ReadE (ReadE (..), succeedReadE)
 import Distribution.Simple.Command
   ( MkOptDescr
   , OptionField (optionName)
@@ -47,6 +48,8 @@ data ProjectFlags = ProjectFlags
   , flagIgnoreProject :: Flag Bool
   -- ^ Whether to ignore the local project (i.e. don't search for cabal.project)
   -- The exact interpretation might be slightly different per command.
+  , flagProjectFileParser :: Flag ProjectFileParser
+  -- ^ The parser to use for the project file.
   }
   deriving (Show, Generic)
 
@@ -56,7 +59,7 @@ defaultProjectFlags =
     { flagProjectDir = mempty
     , flagProjectFile = mempty
     , flagIgnoreProject = toFlag False
-    -- Should we use 'Last' here?
+    , flagProjectFileParser = mempty
     }
 
 projectFlagsOptions :: ShowOrParseArgs -> [OptionField ProjectFlags]
@@ -88,8 +91,32 @@ projectFlagsOptions showOrParseArgs =
             }
       )
       (yesNoOpt showOrParseArgs)
+  , option
+      []
+      ["project-file-parser"]
+      "Set the parser to use for the project file"
+      flagProjectFileParser
+      (\pf flags -> flags{flagProjectFileParser = pf})
+      (reqArg "PARSER" (fmap Flag $ ReadE parseProjectFileParser) projectFileParserPrinter)
   ]
 
+parseProjectFileParser :: String -> Either String ProjectFileParser
+parseProjectFileParser "legacy" = pure LegacyParser
+parseProjectFileParser "fallback" = pure FallbackParser
+parseProjectFileParser "default" = pure defaultProjectFileParser
+parseProjectFileParser "parsec" = pure ParsecParser
+parseProjectFileParser "compare" = pure CompareParser
+parseProjectFileParser _ = Left "Invalid project file parser"
+
+projectFileParserPrinter :: Flag ProjectFileParser -> [String]
+projectFileParserPrinter (Flag parser) =
+  case parser of
+    LegacyParser -> ["legacy"]
+    FallbackParser -> ["fallback"]
+    ParsecParser -> ["parsec"]
+    CompareParser -> ["compare"]
+projectFileParserPrinter NoFlag = []
+
 -- | As almost all commands use 'ProjectFlags' but not all can honour
 -- "ignore-project" flag, provide this utility to remove the flag
 -- parsing from the help message.
diff --git a/cabal-install/src/Distribution/Client/ProjectPlanning.hs b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
index fbd4f758d67..d30a553a4bb 100644
--- a/cabal-install/src/Distribution/Client/ProjectPlanning.hs
+++ b/cabal-install/src/Distribution/Client/ProjectPlanning.hs
@@ -122,6 +122,7 @@ import Distribution.Client.JobControl
 import Distribution.Client.PackageHash
 import Distribution.Client.ProjectConfig
 import Distribution.Client.ProjectConfig.Legacy
+import Distribution.Client.ProjectConfig.Types (defaultProjectFileParser)
 import Distribution.Client.ProjectPlanOutput
 import Distribution.Client.ProjectPlanning.SetupPolicy
   ( NonSetupLibDepSolverPlanPackage (..)
@@ -380,6 +381,7 @@ rebuildProjectConfig
         ( configPath
         , distProjectFile ""
         , (projectConfigHcFlavor, projectConfigHcPath, projectConfigHcPkg)
+        , projectConfigProjectFileParser
         , progsearchpath
         , packageConfigProgramPaths
         , packageConfigProgramPathExtra
@@ -412,7 +414,7 @@ rebuildProjectConfig
 
     return (projectConfig <> cliConfig, localPackages)
     where
-      ProjectConfigShared{projectConfigHcFlavor, projectConfigHcPath, projectConfigHcPkg, projectConfigIgnoreProject, projectConfigConfigFile} =
+      ProjectConfigShared{projectConfigHcFlavor, projectConfigHcPath, projectConfigHcPkg, projectConfigProjectFileParser, projectConfigIgnoreProject, projectConfigConfigFile} =
         projectConfigShared cliConfig
 
       PackageConfig{packageConfigProgramPaths, packageConfigProgramPathExtra} =
@@ -420,10 +422,12 @@ rebuildProjectConfig
 
       -- Read the cabal.project (or implicit config) and combine it with
       -- arguments from the command line
+
+      configFileParser = fromFlagOrDefault defaultProjectFileParser projectConfigProjectFileParser
       --
       phaseReadProjectConfig :: Rebuild ProjectConfigSkeleton
       phaseReadProjectConfig = do
-        readProjectConfig verbosity httpTransport projectConfigIgnoreProject projectConfigConfigFile distDirLayout
+        readProjectConfig verbosity configFileParser httpTransport projectConfigIgnoreProject projectConfigConfigFile distDirLayout
 
       -- Look for all the cabal packages in the project
       -- some of which may be local src dirs, tarballs etc
diff --git a/cabal-install/src/Distribution/Client/ScriptUtils.hs b/cabal-install/src/Distribution/Client/ScriptUtils.hs
index 87c36280503..1c78d537c19 100644
--- a/cabal-install/src/Distribution/Client/ScriptUtils.hs
+++ b/cabal-install/src/Distribution/Client/ScriptUtils.hs
@@ -477,7 +477,7 @@ updateContextAndWriteProjectFile ctx scriptPath scriptExecutable = do
 
   updateContextAndWriteProjectFile' ctx sourcePackage
 
-parseScriptBlock :: BS.ByteString -> ParseResult Executable
+parseScriptBlock :: BS.ByteString -> ParseResult src Executable
 parseScriptBlock str =
   case readFields str of
     Right fs -> do
diff --git a/cabal-install/src/Distribution/Client/Types/AllowNewer.hs b/cabal-install/src/Distribution/Client/Types/AllowNewer.hs
index 0a5700174b8..53c55ef08b6 100644
--- a/cabal-install/src/Distribution/Client/Types/AllowNewer.hs
+++ b/cabal-install/src/Distribution/Client/Types/AllowNewer.hs
@@ -101,6 +101,12 @@ instance Pretty RelaxedDep where
 instance Parsec RelaxedDep where
   parsec = P.char '*' *> relaxedDepStarP <|> (parsec >>= relaxedDepPkgidP)
 
+instance Parsec AllowOlder where
+  parsec = AllowOlder <$> parsec
+
+instance Parsec AllowNewer where
+  parsec = AllowNewer <$> parsec
+
 -- continuation after *
 relaxedDepStarP :: CabalParsing m => m RelaxedDep
 relaxedDepStarP =
diff --git a/cabal-install/src/Distribution/Client/Types/Repo.hs b/cabal-install/src/Distribution/Client/Types/Repo.hs
index 83ecc454863..d3caac872db 100644
--- a/cabal-install/src/Distribution/Client/Types/Repo.hs
+++ b/cabal-install/src/Distribution/Client/Types/Repo.hs
@@ -4,6 +4,10 @@ module Distribution.Client.Types.Repo
   ( -- * Remote repository
     RemoteRepo (..)
   , emptyRemoteRepo
+  , remoteRepoKeyThresholdLens
+  , remoteRepoRootKeysLens
+  , remoteRepoSecureLens
+  , remoteRepoURILens
 
     -- * Local repository (no-index)
   , LocalRepo (..)
@@ -17,6 +21,7 @@ module Distribution.Client.Types.Repo
   , maybeRepoRemote
 
     -- * Windows
+  , asPosixPath
   , normaliseFileNoIndexURI
   ) where
 
@@ -29,6 +34,7 @@ import Distribution.Simple.Utils (toUTF8BS)
 import Distribution.System (OS (Windows))
 
 import Distribution.Client.HashValue (hashValue, showHashValue, truncateHash)
+import Distribution.Compat.Lens
 
 import qualified Data.ByteString.Lazy.Char8 as LBS
 import qualified Distribution.Compat.CharParsing as P
@@ -97,6 +103,22 @@ instance Parsec RemoteRepo where
 emptyRemoteRepo :: RepoName -> RemoteRepo
 emptyRemoteRepo name = RemoteRepo name nullURI Nothing [] 0 False
 
+remoteRepoURILens :: Lens' RemoteRepo URI
+remoteRepoURILens f s = fmap (\x -> s{remoteRepoURI = x}) (f (remoteRepoURI s))
+{-# INLINE remoteRepoURILens #-}
+
+remoteRepoSecureLens :: Lens' RemoteRepo (Maybe Bool)
+remoteRepoSecureLens f s = fmap (\x -> s{remoteRepoSecure = x}) (f (remoteRepoSecure s))
+{-# INLINE remoteRepoSecureLens #-}
+
+remoteRepoRootKeysLens :: Lens' RemoteRepo [String]
+remoteRepoRootKeysLens f s = fmap (\x -> s{remoteRepoRootKeys = x}) (f (remoteRepoRootKeys s))
+{-# INLINE remoteRepoRootKeysLens #-}
+
+remoteRepoKeyThresholdLens :: Lens' RemoteRepo Int
+remoteRepoKeyThresholdLens f s = fmap (\x -> s{remoteRepoKeyThreshold = x}) (f (remoteRepoKeyThreshold s))
+{-# INLINE remoteRepoKeyThresholdLens #-}
+
 -------------------------------------------------------------------------------
 -- Local repository
 -------------------------------------------------------------------------------
@@ -230,8 +252,10 @@ normaliseFileNoIndexURI os uri@(URI scheme _auth path query fragment)
   , Windows <- os =
       URI scheme Nothing (asPosixPath path) query fragment
   | otherwise = uri
-  where
-    asPosixPath p =
-      -- We don't use 'isPathSeparator' because @Windows.isPathSeparator
-      -- Posix.pathSeparator == True@.
-      [if x == Windows.pathSeparator then Posix.pathSeparator else x | x <- p]
+
+-- | Convert a path to POSIX-style.
+asPosixPath :: FilePath -> FilePath
+asPosixPath p =
+  -- We don't use 'isPathSeparator' because @Windows.isPathSeparator
+  -- Posix.pathSeparator == True@.
+  [if x == Windows.pathSeparator then Posix.pathSeparator else x | x <- p]
diff --git a/cabal-install/src/Distribution/Client/Types/WriteGhcEnvironmentFilesPolicy.hs b/cabal-install/src/Distribution/Client/Types/WriteGhcEnvironmentFilesPolicy.hs
index 042b62d997a..6db210025ee 100644
--- a/cabal-install/src/Distribution/Client/Types/WriteGhcEnvironmentFilesPolicy.hs
+++ b/cabal-install/src/Distribution/Client/Types/WriteGhcEnvironmentFilesPolicy.hs
@@ -5,6 +5,8 @@ module Distribution.Client.Types.WriteGhcEnvironmentFilesPolicy
   ) where
 
 import Distribution.Client.Compat.Prelude
+import qualified Distribution.Compat.CharParsing as P
+import Distribution.Parsec
 import Prelude ()
 
 -- | Whether 'v2-build' should write a .ghc.environment file after
@@ -19,3 +21,16 @@ data WriteGhcEnvironmentFilesPolicy
 
 instance Binary WriteGhcEnvironmentFilesPolicy
 instance Structured WriteGhcEnvironmentFilesPolicy
+
+instance Parsec WriteGhcEnvironmentFilesPolicy where
+  parsec = do
+    token <- parsecToken
+    case token of
+      "always" -> return AlwaysWriteGhcEnvironmentFiles
+      "never" -> return NeverWriteGhcEnvironmentFiles
+      "ghc8.4.4+" -> return WriteGhcEnvironmentFilesOnlyForGhc844AndNewer
+      policy ->
+        P.unexpected $
+          "Cannot parse the GHC environment file write policy '"
+            <> policy
+            <> "'"
diff --git a/cabal-install/src/Distribution/Client/Utils/Newtypes.hs b/cabal-install/src/Distribution/Client/Utils/Newtypes.hs
new file mode 100644
index 00000000000..aa60eea697c
--- /dev/null
+++ b/cabal-install/src/Distribution/Client/Utils/Newtypes.hs
@@ -0,0 +1,120 @@
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+
+-- | This module provides @newtype@ wrappers to be used with "Distribution.FieldGrammar".
+-- Whenever we can not provide a Parsec instance for a type, we need to wrap it in a newtype and define the instance.
+module Distribution.Client.Utils.Newtypes
+  ( NumJobs (..)
+  , PackageDBNT (..)
+  , AllowNewerNT (..)
+  , AllowOlderNT (..)
+  , ProjectConstraints (..)
+  , MaxBackjumps (..)
+  , URI_NT (..)
+  , KeyThreshold (..)
+  )
+where
+
+import Distribution.Client.Compat.Prelude
+import Distribution.Client.Targets (UserConstraint)
+import Distribution.Client.Types.AllowNewer (AllowNewer (..), AllowOlder (..))
+import Distribution.Compat.CharParsing
+import Distribution.Compat.Newtype
+import Distribution.Parsec
+import Distribution.Simple.Compiler (PackageDBCWD, interpretPackageDB, readPackageDb)
+import Distribution.Solver.Types.ConstraintSource (ConstraintSource (..))
+import Network.URI (URI, parseURI)
+
+newtype PackageDBNT = PackageDBNT {getPackageDBNT :: Maybe PackageDBCWD}
+
+instance Newtype (Maybe PackageDBCWD) PackageDBNT
+
+instance Parsec PackageDBNT where
+  parsec = parsecPackageDB
+
+parsecPackageDB :: CabalParsing m => m PackageDBNT
+parsecPackageDB = PackageDBNT . fmap (interpretPackageDB Nothing) . readPackageDb <$> parsecToken
+
+newtype NumJobs = NumJobs {getNumJobs :: Maybe Int}
+
+instance Newtype (Maybe Int) NumJobs
+
+instance Parsec NumJobs where
+  parsec = parsecNumJobs
+
+parsecNumJobs :: CabalParsing m => m NumJobs
+parsecNumJobs = ncpus <|> numJobs
+  where
+    ncpus = string "$ncpus" >> return (NumJobs Nothing)
+    numJobs = do
+      num <- integral
+      if num < (1 :: Int)
+        then do
+          parsecWarning PWTOther "The number of jobs should be 1 or more."
+          return (NumJobs Nothing)
+        else return (NumJobs $ Just num)
+
+newtype URI_NT = URI_NT {getURI_NT :: URI}
+
+instance Newtype (URI) URI_NT
+
+instance Parsec URI_NT where
+  parsec = parsecURI_NT
+
+parsecURI_NT :: CabalParsing m => m URI_NT
+parsecURI_NT = do
+  token <- parsecToken'
+  case parseURI token of
+    Nothing -> fail $ "failed to parse URI " <> token
+    Just uri -> return $ URI_NT uri
+
+newtype KeyThreshold = KeyThreshold {getKeyThreshold :: Int}
+
+instance Newtype Int KeyThreshold
+
+instance Parsec KeyThreshold where
+  parsec = KeyThreshold <$> integral
+
+newtype ProjectConstraints = ProjectConstraints {getProjectConstraints :: (UserConstraint, ConstraintSource)}
+
+instance Newtype (UserConstraint, ConstraintSource) ProjectConstraints
+
+instance Parsec ProjectConstraints where
+  parsec = parsecProjectConstraints
+
+-- | Parse 'ProjectConstraints'. As the 'CabalParsing' class does not have access to the file we parse,
+-- ConstraintSource is first unknown and we set it afterwards
+parsecProjectConstraints :: CabalParsing m => m ProjectConstraints
+parsecProjectConstraints = do
+  userConstraint <- parsec
+  return $ ProjectConstraints (userConstraint, ConstraintSourceUnknown)
+
+newtype MaxBackjumps = MaxBackjumps {getMaxBackjumps :: Int}
+
+instance Newtype Int MaxBackjumps
+
+instance Parsec MaxBackjumps where
+  parsec = parseMaxBackjumps
+
+parseMaxBackjumps :: CabalParsing m => m MaxBackjumps
+parseMaxBackjumps = MaxBackjumps <$> integral
+
+newtype AllowNewerNT = AllowNewerNT {getAllowNewerNT :: Maybe AllowNewer}
+
+instance Newtype (Maybe AllowNewer) AllowNewerNT
+
+instance Parsec AllowNewerNT where
+  parsec = parsecAllowNewer
+
+parsecAllowNewer :: CabalParsing m => m AllowNewerNT
+parsecAllowNewer = AllowNewerNT . Just <$> parsec
+
+newtype AllowOlderNT = AllowOlderNT {getAllowOlderNT :: Maybe AllowOlder}
+
+instance Newtype (Maybe AllowOlder) AllowOlderNT
+
+instance Parsec AllowOlderNT where
+  parsec = parsecAllowOlder
+
+parsecAllowOlder :: CabalParsing m => m AllowOlderNT
+parsecAllowOlder = AllowOlderNT . Just <$> parsec
diff --git a/cabal-install/src/Distribution/Client/Utils/Parsec.hs b/cabal-install/src/Distribution/Client/Utils/Parsec.hs
index abc9ddd1321..d7fcbf4778d 100644
--- a/cabal-install/src/Distribution/Client/Utils/Parsec.hs
+++ b/cabal-install/src/Distribution/Client/Utils/Parsec.hs
@@ -1,105 +1,90 @@
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+
 module Distribution.Client.Utils.Parsec
-  ( renderParseError
+  ( remoteRepoGrammar
+
+    -- ** Flag
+  , alaFlag
+  , Flag'
+
+    -- ** NubList
+  , alaNubList
+  , alaNubList'
+  , NubList'
+
+    -- ** Newtype wrappers
+  , module Distribution.Client.Utils.Newtypes
   ) where
 
 import Distribution.Client.Compat.Prelude
-import System.FilePath (normalise)
+import Distribution.Compat.Newtype
 import Prelude ()
 
-import qualified Data.ByteString as BS
-import qualified Data.ByteString.Char8 as BS8
-
-import Distribution.Parsec (PError (..), PWarning (..), Position (..), showPos, zeroPos)
-import Distribution.Simple.Utils (fromUTF8BS)
-
--- | Render parse error highlighting the part of the input file.
-renderParseError
-  :: FilePath
-  -> BS.ByteString
-  -> NonEmpty PError
-  -> [PWarning]
-  -> String
-renderParseError filepath contents errors warnings =
-  unlines $
-    [ "Errors encountered when parsing cabal file " <> filepath <> ":"
-    ]
-      ++ renderedErrors
-      ++ renderedWarnings
-  where
-    filepath' = normalise filepath
-
-    -- lines of the input file. 'lines' is taken, so they are called rows
-    -- contents, line number, whether it's empty line
-    rows :: [(String, Int, Bool)]
-    rows = zipWith f (BS8.lines contents) [1 ..]
-      where
-        f bs i = let s = fromUTF8BS bs in (s, i, isEmptyOrComment s)
-
-    rowsZipper = listToZipper rows
-
-    isEmptyOrComment :: String -> Bool
-    isEmptyOrComment s = case dropWhile (== ' ') s of
-      "" -> True -- empty
-      ('-' : '-' : _) -> True -- comment
-      _ -> False
-
-    renderedErrors = concatMap renderError errors
-    renderedWarnings = concatMap renderWarning warnings
-
-    renderError :: PError -> [String]
-    renderError (PError pos@(Position row col) msg)
-      -- if position is 0:0, then it doesn't make sense to show input
-      -- looks like, Parsec errors have line-feed in them
-      | pos == zeroPos = msgs
-      | otherwise = msgs ++ formatInput row col
-      where
-        msgs = ["", filepath' ++ ":" ++ showPos pos ++ ": error:", trimLF msg, ""]
-
-    renderWarning :: PWarning -> [String]
-    renderWarning (PWarning _ pos@(Position row col) msg)
-      | pos == zeroPos = msgs
-      | otherwise = msgs ++ formatInput row col
-      where
-        msgs = ["", filepath' ++ ":" ++ showPos pos ++ ": warning:", trimLF msg, ""]
-
-    -- sometimes there are (especially trailing) newlines.
-    trimLF :: String -> String
-    trimLF = dropWhile (== '\n') . reverse . dropWhile (== '\n') . reverse
-
-    -- format line: prepend the given line number
-    formatInput :: Int -> Int -> [String]
-    formatInput row col = case advance (row - 1) rowsZipper of
-      Zipper xs ys -> before ++ after
-        where
-          before = case span (\(_, _, b) -> b) xs of
-            (_, []) -> []
-            (zs, z : _) -> map formatInputLine $ z : reverse zs
-
-          after = case ys of
-            [] -> []
-            (z : _zs) ->
-              [ formatInputLine z -- error line
-              , "      | " ++ replicate (col - 1) ' ' ++ "^" -- pointer: ^
-              ]
-    -- do we need rows after?
-    -- ++ map formatInputLine (take 1 zs)           -- one row after
-
-    formatInputLine :: (String, Int, Bool) -> String
-    formatInputLine (str, row, _) = leftPadShow row ++ " | " ++ str
-
-    -- hopefully we don't need to work with over 99999 lines .cabal files
-    -- at that point small glitches in error messages are hopefully fine.
-    leftPadShow :: Int -> String
-    leftPadShow n = let s = show n in replicate (5 - length s) ' ' ++ s
-
-data Zipper a = Zipper [a] [a]
-
-listToZipper :: [a] -> Zipper a
-listToZipper = Zipper []
-
-advance :: Int -> Zipper a -> Zipper a
-advance n z@(Zipper xs ys)
-  | n <= 0 = z
-  | otherwise = case ys of
-      [] -> z
-      (y : ys') -> advance (n - 1) $ Zipper (y : xs) ys'
+import Distribution.Client.Types.Repo
+import Distribution.Client.Types.RepoName
+import Distribution.Client.Utils.Newtypes
+import Distribution.FieldGrammar
+import Distribution.Simple.Flag
+import Distribution.Utils.NubList (NubList (..))
+import qualified Distribution.Utils.NubList as NubList
+
+-- | Like 'List' for usage with a 'FieldGrammar', but for 'Flag'.
+-- This enables to parse type aliases such as 'FilePath' that do not have 'Parsec' instances
+-- by using newtype variants such as 'FilePathNT'.
+-- For example, if you need to parse a 'Flag FilePath', you can use 'alaFlag' FilePathNT'.
+newtype Flag' b a = Flag' {_getFlag :: Flag a}
+
+-- | 'Flag'' constructor, with additional phantom argument to constrain the resulting type
+alaFlag :: (a -> b) -> Flag a -> Flag' b a
+alaFlag _ = Flag'
+
+instance Newtype (Flag a) (Flag' wrapper a)
+
+instance (Newtype a b, Parsec b) => Parsec (Flag' b a) where
+  parsec = pack . toFlag . (unpack :: b -> a) <$> parsec
+
+instance (Newtype a b, Pretty b) => Pretty (Flag' b a) where
+  pretty = pretty . (pack :: a -> b) . fromFlag . unpack
+
+-- | Like 'List' for usage with a 'FieldGrammar', but for 'NubList'.
+newtype NubList' sep b a = NubList' {_getNubList :: NubList a}
+
+-- | 'alaNubList' and 'alaNubList'' are simply 'NubList'' constructor, with additional phantom
+-- arguments to constrain the resulting type
+--
+-- >>> :t alaNubList VCat
+-- alaNubList VCat :: NubList a -> NubList' VCat (Identity a) a
+--
+-- >>> :t alaNubList' FSep Token
+-- alaNubList' FSep Token
+--   :: NubList String -> NubList' FSep Token String
+--
+-- >>> unpack' (alaNubList' FSep Token) <$> eitherParsec "foo bar foo"
+-- Right ["foo","bar"]
+alaNubList :: sep -> NubList a -> NubList' sep (Identity a) a
+alaNubList _ = NubList'
+
+-- | More general version of 'alaNubList'.
+alaNubList' :: sep -> (a -> b) -> NubList a -> NubList' sep b a
+alaNubList' _ _ = NubList'
+
+instance Newtype (NubList a) (NubList' sep wrapper a)
+
+instance (Newtype a b, Ord a, Sep sep, Parsec b) => Parsec (NubList' sep b a) where
+  parsec = pack . NubList.toNubList . map (unpack :: b -> a) <$> parseSep (Proxy :: Proxy sep) parsec
+
+instance (Newtype a b, Sep sep, Pretty b) => Pretty (NubList' sep b a) where
+  pretty = prettySep (Proxy :: Proxy sep) . map (pretty . (pack :: a -> b)) . NubList.fromNubList . unpack
+
+remoteRepoGrammar :: RepoName -> ParsecFieldGrammar RemoteRepo RemoteRepo
+remoteRepoGrammar name =
+  RemoteRepo
+    <$> pure name
+    <*> uniqueFieldAla "url" URI_NT remoteRepoURILens
+    <*> optionalField "secure" remoteRepoSecureLens
+    <*> monoidalFieldAla "root-keys" (alaList' FSep Token) remoteRepoRootKeysLens
+    <*> optionalFieldDefAla "key-threshold" KeyThreshold remoteRepoKeyThresholdLens 0
+    <*> pure False -- we don't parse remoteRepoShouldTryHttps
diff --git a/cabal-install/tests/UnitTests/Distribution/Client/ProjectConfig.hs b/cabal-install/tests/UnitTests/Distribution/Client/ProjectConfig.hs
index bf69b20ee04..caee779671b 100644
--- a/cabal-install/tests/UnitTests/Distribution/Client/ProjectConfig.hs
+++ b/cabal-install/tests/UnitTests/Distribution/Client/ProjectConfig.hs
@@ -606,6 +606,7 @@ instance Arbitrary ProjectConfigShared where
     projectConfigConfigFile <- arbitraryFlag arbitraryShortToken
     projectConfigProjectDir <- arbitraryFlag arbitraryShortToken
     projectConfigProjectFile <- arbitraryFlag arbitraryShortToken
+    projectConfigProjectFileParser <- arbitraryFlag arbitrary
     projectConfigIgnoreProject <- arbitrary
     projectConfigHcFlavor <- arbitrary
     projectConfigHcPath <- arbitraryFlag arbitraryShortToken
@@ -652,6 +653,7 @@ instance Arbitrary ProjectConfigShared where
         <*> shrinker projectConfigConfigFile
         <*> shrinker projectConfigProjectDir
         <*> shrinker projectConfigProjectFile
+        <*> shrinker projectConfigProjectFileParser
         <*> shrinker projectConfigIgnoreProject
         <*> shrinker projectConfigHcFlavor
         <*> shrinkerAla (fmap NonEmpty) projectConfigHcPath
@@ -691,6 +693,9 @@ instance Arbitrary ProjectConfigShared where
 projectConfigConstraintSource :: ConstraintSource
 projectConfigConstraintSource = ConstraintSourceProjectConfig nullProjectConfigPath
 
+instance Arbitrary ProjectFileParser where
+  arbitrary = elements [ParsecParser, LegacyParser, FallbackParser, CompareParser]
+
 instance Arbitrary ProjectConfigProvenance where
   arbitrary = elements [Implicit, Explicit (ProjectConfigPath $ "cabal.project" :| [])]
 
diff --git a/cabal-install/tests/UnitTests/Distribution/Client/TreeDiffInstances.hs b/cabal-install/tests/UnitTests/Distribution/Client/TreeDiffInstances.hs
index 179fef5688a..ef4f9fb7c9f 100644
--- a/cabal-install/tests/UnitTests/Distribution/Client/TreeDiffInstances.hs
+++ b/cabal-install/tests/UnitTests/Distribution/Client/TreeDiffInstances.hs
@@ -63,6 +63,7 @@ instance ToExpr ProjectConfig
 instance ToExpr ProjectConfigBuildOnly
 instance ToExpr ProjectConfigProvenance
 instance ToExpr ProjectConfigShared
+instance ToExpr ProjectFileParser
 instance ToExpr RelaxDepMod
 instance ToExpr RelaxDeps
 instance ToExpr RelaxDepScope
diff --git a/cabal-testsuite/PackageTests/Check/ConfiguredPackage/Sanity/NoName/cabal.out b/cabal-testsuite/PackageTests/Check/ConfiguredPackage/Sanity/NoName/cabal.out
index 95a718c5798..decf3cfcca4 100644
--- a/cabal-testsuite/PackageTests/Check/ConfiguredPackage/Sanity/NoName/cabal.out
+++ b/cabal-testsuite/PackageTests/Check/ConfiguredPackage/Sanity/NoName/cabal.out
@@ -1,4 +1,8 @@
 # cabal check
-Warning: pkg.cabal:0:0: "name" field missing
 Error: [Cabal-7035]
-parse error
+Error parsing cabal file pkg.cabal:
+
+pkg.cabal: error:
+  "name" field missing
+
+
diff --git a/cabal-testsuite/PackageTests/Check/ConfiguredPackage/Sanity/NoVersion/cabal.out b/cabal-testsuite/PackageTests/Check/ConfiguredPackage/Sanity/NoVersion/cabal.out
index e2b3c055434..a539f19dbd2 100644
--- a/cabal-testsuite/PackageTests/Check/ConfiguredPackage/Sanity/NoVersion/cabal.out
+++ b/cabal-testsuite/PackageTests/Check/ConfiguredPackage/Sanity/NoVersion/cabal.out
@@ -1,4 +1,8 @@
 # cabal check
-Warning: pkg.cabal:0:0: "version" field missing
 Error: [Cabal-7035]
-parse error
+Error parsing cabal file pkg.cabal:
+
+pkg.cabal: error:
+  "version" field missing
+
+
diff --git a/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.out b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.out
index 73d7d091749..4e2cfe368c3 100644
--- a/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.out
+++ b/cabal-testsuite/PackageTests/ConditionalAndImport/cabal.out
@@ -12,54 +12,100 @@ Installing executable some-exe in <PATH>
 Warning: The directory <ROOT>/cabal.dist/home/.cabal/store/ghc-<GHCVER>/incoming/new-<RAND><ROOT>/cabal.dist/home/.cabal/store/ghc-<GHCVER>/<PACKAGE>-<HASH>/bin is not in the system search path.
 # checking cyclical loopback of a project importing itself
 # cabal v2-build
-Error: [Cabal-7090]
+Error: [Cabal-7167]
 Error parsing project file cyclical-0-self.project:
- - cyclical import of cyclical-0-self.project;
-     cyclical-0-self.project
-       imported by: cyclical-0-self.project
+
+cyclical-0-self.project:3:1: error:
+  cyclical import of cyclical-0-self.project;
+    cyclical-0-self.project
+      imported by: cyclical-0-self.project
+      1 | packages: .
+      2 | 
+      3 | import: cyclical-0-self.project
+        | ^
+
+
 # checking cyclical with hops; out and back
 # cabal v2-build
-Error: [Cabal-7090]
+Error: [Cabal-7167]
 Error parsing project file cyclical-1-out-back.config:
- - cyclical import of cyclical-1-out-back.project;
-     cyclical-1-out-back.project
-       imported by: cyclical-1-out-back.config
-       imported by: cyclical-1-out-back.project
+  imported by: cyclical-1-out-back.project
+
+cyclical-1-out-back.config:1:1: error:
+  cyclical import of cyclical-1-out-back.project;
+    cyclical-1-out-back.project
+      imported by: cyclical-1-out-back.config
+      imported by: cyclical-1-out-back.project
+      1 | import: cyclical-1-out-back.project
+        | ^
+
+
 # checking cyclical with hops; out to a config that imports itself
 # cabal v2-build
-Error: [Cabal-7090]
+Error: [Cabal-7167]
 Error parsing project file cyclical-1-out-self.config:
- - cyclical import of cyclical-1-out-self.config;
-     cyclical-1-out-self.config
-       imported by: cyclical-1-out-self.config
-       imported by: cyclical-1-out-self.project
+  imported by: cyclical-1-out-self.project
+
+cyclical-1-out-self.config:1:1: error:
+  cyclical import of cyclical-1-out-self.config;
+    cyclical-1-out-self.config
+      imported by: cyclical-1-out-self.config
+      imported by: cyclical-1-out-self.project
+      1 | import: cyclical-1-out-self.config
+        | ^
+
+
 # checking cyclical with hops; out, out, twice back
 # cabal v2-build
-Error: [Cabal-7090]
+Error: [Cabal-7167]
 Error parsing project file cyclical-2-out-out-backback-b.config:
- - cyclical import of cyclical-2-out-out-backback.project;
-     cyclical-2-out-out-backback.project
-       imported by: cyclical-2-out-out-backback-b.config
-       imported by: cyclical-2-out-out-backback-a.config
-       imported by: cyclical-2-out-out-backback.project
+  imported by: cyclical-2-out-out-backback-a.config
+  imported by: cyclical-2-out-out-backback.project
+
+cyclical-2-out-out-backback-b.config:1:1: error:
+  cyclical import of cyclical-2-out-out-backback.project;
+    cyclical-2-out-out-backback.project
+      imported by: cyclical-2-out-out-backback-b.config
+      imported by: cyclical-2-out-out-backback-a.config
+      imported by: cyclical-2-out-out-backback.project
+      1 | import: cyclical-2-out-out-backback.project
+        | ^
+
+
 # checking cyclical with hops; out, out, once back
 # cabal v2-build
-Error: [Cabal-7090]
+Error: [Cabal-7167]
 Error parsing project file cyclical-2-out-out-back-b.config:
- - cyclical import of cyclical-2-out-out-back-a.config;
-     cyclical-2-out-out-back-a.config
-       imported by: cyclical-2-out-out-back-b.config
-       imported by: cyclical-2-out-out-back-a.config
-       imported by: cyclical-2-out-out-back.project
+  imported by: cyclical-2-out-out-back-a.config
+  imported by: cyclical-2-out-out-back.project
+
+cyclical-2-out-out-back-b.config:1:1: error:
+  cyclical import of cyclical-2-out-out-back-a.config;
+    cyclical-2-out-out-back-a.config
+      imported by: cyclical-2-out-out-back-b.config
+      imported by: cyclical-2-out-out-back-a.config
+      imported by: cyclical-2-out-out-back.project
+      1 | import: cyclical-2-out-out-back-a.config
+        | ^
+
+
 # checking cyclical with hops; out, out to a config that imports itself
 # cabal v2-build
-Error: [Cabal-7090]
+Error: [Cabal-7167]
 Error parsing project file cyclical-2-out-out-self-b.config:
- - cyclical import of cyclical-2-out-out-self-b.config;
-     cyclical-2-out-out-self-b.config
-       imported by: cyclical-2-out-out-self-b.config
-       imported by: cyclical-2-out-out-self-a.config
-       imported by: cyclical-2-out-out-self.project
+  imported by: cyclical-2-out-out-self-a.config
+  imported by: cyclical-2-out-out-self.project
+
+cyclical-2-out-out-self-b.config:1:1: error:
+  cyclical import of cyclical-2-out-out-self-b.config;
+    cyclical-2-out-out-self-b.config
+      imported by: cyclical-2-out-out-self-b.config
+      imported by: cyclical-2-out-out-self-a.config
+      imported by: cyclical-2-out-out-self.project
+      1 | import: cyclical-2-out-out-self-b.config
+        | ^
+
+
 # checking that cyclical check doesn't false-positive on same file names in different folders; hoping within a folder and then into a subfolder
 # cabal v2-build
 Resolving dependencies...
@@ -74,31 +120,55 @@ Building library for my-0.1...
 Up to date
 # checking that cyclical check catches a same file name that imports itself
 # cabal v2-build
-Error: [Cabal-7090]
+Error: [Cabal-7167]
 Error parsing project file same-filename/cyclical-same-filename-out-out-self.config:
- - cyclical import of same-filename/cyclical-same-filename-out-out-self.config;
-     same-filename/cyclical-same-filename-out-out-self.config
-       imported by: same-filename/cyclical-same-filename-out-out-self.config
-       imported by: cyclical-same-filename-out-out-self.config
-       imported by: cyclical-same-filename-out-out-self.project
+  imported by: cyclical-same-filename-out-out-self.config
+  imported by: cyclical-same-filename-out-out-self.project
+
+same-filename/cyclical-same-filename-out-out-self.config:1:1: error:
+  cyclical import of same-filename/cyclical-same-filename-out-out-self.config;
+    same-filename/cyclical-same-filename-out-out-self.config
+      imported by: same-filename/cyclical-same-filename-out-out-self.config
+      imported by: cyclical-same-filename-out-out-self.config
+      imported by: cyclical-same-filename-out-out-self.project
+      1 | import: cyclical-same-filename-out-out-self.config
+        | ^
+
+
 # checking that cyclical check catches importing its importer (with the same file name)
 # cabal v2-build
-Error: [Cabal-7090]
+Error: [Cabal-7167]
 Error parsing project file same-filename/cyclical-same-filename-out-out-backback.config:
- - cyclical import of cyclical-same-filename-out-out-backback.project;
-     cyclical-same-filename-out-out-backback.project
-       imported by: same-filename/cyclical-same-filename-out-out-backback.config
-       imported by: cyclical-same-filename-out-out-backback.config
-       imported by: cyclical-same-filename-out-out-backback.project
+  imported by: cyclical-same-filename-out-out-backback.config
+  imported by: cyclical-same-filename-out-out-backback.project
+
+same-filename/cyclical-same-filename-out-out-backback.config:1:1: error:
+  cyclical import of cyclical-same-filename-out-out-backback.project;
+    cyclical-same-filename-out-out-backback.project
+      imported by: same-filename/cyclical-same-filename-out-out-backback.config
+      imported by: cyclical-same-filename-out-out-backback.config
+      imported by: cyclical-same-filename-out-out-backback.project
+      1 | import: ../cyclical-same-filename-out-out-backback.project
+        | ^
+
+
 # checking that cyclical check catches importing its importer's importer (hopping over same file names)
 # cabal v2-build
-Error: [Cabal-7090]
+Error: [Cabal-7167]
 Error parsing project file same-filename/cyclical-same-filename-out-out-back.config:
- - cyclical import of cyclical-same-filename-out-out-back.config;
-     cyclical-same-filename-out-out-back.config
-       imported by: same-filename/cyclical-same-filename-out-out-back.config
-       imported by: cyclical-same-filename-out-out-back.config
-       imported by: cyclical-same-filename-out-out-back.project
+  imported by: cyclical-same-filename-out-out-back.config
+  imported by: cyclical-same-filename-out-out-back.project
+
+same-filename/cyclical-same-filename-out-out-back.config:1:1: error:
+  cyclical import of cyclical-same-filename-out-out-back.config;
+    cyclical-same-filename-out-out-back.config
+      imported by: same-filename/cyclical-same-filename-out-out-back.config
+      imported by: cyclical-same-filename-out-out-back.config
+      imported by: cyclical-same-filename-out-out-back.project
+      1 | import: ../cyclical-same-filename-out-out-back.config
+        | ^
+
+
 # checking that imports work skipping into a subfolder and then back out again and again
 # cabal v2-build
 Up to date
@@ -129,8 +199,12 @@ After searching the rest of the dependency tree exhaustively, these were the goa
 Up to date
 # checking bad conditional
 # cabal v2-build
-Error: [Cabal-7090]
-Error parsing project file <ROOT>/bad-conditional.project:
- - Cannot set compiler in a conditional clause of a cabal project file
+Error: [Cabal-7167]
+Error parsing project file bad-conditional.project:
+
+bad-conditional.project: error:
+  Cannot set compiler in a conditional clause of a cabal project file
+
+
 # checking that missing package message lists configuration provenance
 # cabal v2-build
diff --git a/cabal-testsuite/PackageTests/IndexCabalFileParseError/cabal.out b/cabal-testsuite/PackageTests/IndexCabalFileParseError/cabal.out
index 8d891bd421e..485ef98565a 100644
--- a/cabal-testsuite/PackageTests/IndexCabalFileParseError/cabal.out
+++ b/cabal-testsuite/PackageTests/IndexCabalFileParseError/cabal.out
@@ -1,19 +1,20 @@
 # cabal v2-update
 Downloading the latest package list from test-local-repo
-Warning: In <ROOT>/cabal.dist/repo/my-lib-1.0.tar.gz: Errors encountered when parsing cabal file my-lib-1.0/my-lib.cabal:
+Warning: In <ROOT>/cabal.dist/repo/my-lib-1.0.tar.gz: Error parsing cabal file my-lib-1.0/my-lib.cabal:
 
-my-lib-1.0/my-lib.cabal:4:22: error:
-unexpected Unknown SPDX license identifier: 'puppy' 
+my-lib-1.0/my-lib.cabal:5:1: warning:
+  Unknown field: "puppy"
+      4 | license:        puppy license :)
+      5 | puppy:          teehee!
+        | ^
 
-    3 | version:        1.0
-    4 | license:        puppy license :)
-      |                      ^
 
-my-lib-1.0/my-lib.cabal:5:1: warning:
-Unknown field: "puppy"
+my-lib-1.0/my-lib.cabal:4:22: error:
+  unexpected Unknown SPDX license identifier: 'puppy' 
+      3 | version:        1.0
+      4 | license:        puppy license :)
+        |                      ^
+
 
-    4 | license:        puppy license :)
-    5 | puppy:          teehee!
-      | ^
 Error: [Cabal-7046]
 Failed to read my-lib-1.0/my-lib.cabal from archive <ROOT>/cabal.dist/repo/my-lib-1.0.tar.gz
diff --git a/cabal-testsuite/PackageTests/ProjectConfig/FieldStanzaConfusion/cabal.out b/cabal-testsuite/PackageTests/ProjectConfig/FieldStanzaConfusion/cabal.out
index b94b99a9a08..5423e2454ec 100644
--- a/cabal-testsuite/PackageTests/ProjectConfig/FieldStanzaConfusion/cabal.out
+++ b/cabal-testsuite/PackageTests/ProjectConfig/FieldStanzaConfusion/cabal.out
@@ -1,4 +1,13 @@
 # cabal build
-Error: [Cabal-7090]
-Error parsing project file cabal.project:4:
-  - 'source-repository-package' is a stanza, not a field. Remove the trailing ':' to parse a stanza.
+Error: [Cabal-7167]
+Error parsing project file cabal.project:
+
+cabal.project:4:1: error:
+  'source-repository-package' is a stanza, not a field. Remove the trailing ':' to parse a stanza.
+      1 | packages: .
+      2 | 
+      3 | -- This is an error; a trailing `:` is syntax for a field, not a stanza!
+      4 | source-repository-package:
+        | ^
+
+
diff --git a/cabal-testsuite/PackageTests/ProjectImport/ParseErrorProvenance/cabal.out b/cabal-testsuite/PackageTests/ProjectImport/ParseErrorProvenance/cabal.out
index d3c6ddb66c6..b2d1fd35fc7 100644
--- a/cabal-testsuite/PackageTests/ProjectImport/ParseErrorProvenance/cabal.out
+++ b/cabal-testsuite/PackageTests/ProjectImport/ParseErrorProvenance/cabal.out
@@ -1,25 +1,39 @@
 # cabal v2-build
 Warnings found while parsing the project file, else.project:
- - dir-else/else.config: Unrecognized section '_' on line 3
+ - dir-else/else.config:3:5: Invalid subsection "_"
 # cabal v2-build
-Error: [Cabal-7090]
-Error parsing project file cabal.project:3:
- - Failed to parse 'if(_)' with error:
-     "<condition>" (line 1, column 1): unexpected SecArgName (Position 1 4) "_"
+Error: [Cabal-7167]
+Error parsing project file cabal.project:
+
+cabal.project:3:4: error:
+  unexpected SecArgName (Position 3 4) "_"
+      3 | if _
+        |    ^
+
+
 # cabal v2-build
-Error: [Cabal-7090]
-Error parsing project file dir-if/if.config:3:
- - dir-if/if.config
-     imported by: if.project
-   Failed to parse 'if(_)' with error:
-     "<condition>" (line 1, column 1): unexpected SecArgName (Position 1 4) "_"
+Error: [Cabal-7167]
+Error parsing project file dir-if/if.config:
+  imported by: if.project
+
+dir-if/if.config:3:4: error:
+  unexpected SecArgName (Position 3 4) "_"
+      3 | if _
+        |    ^
+
+
 # cabal v2-build
-Error: [Cabal-7090]
-Error parsing project file dir-elif/elif.config:4:
- - dir-elif/elif.config
-     imported by: elif.project
-   Failed to parse 'elif(_)' with error:
-     "<condition>" (line 1, column 1): unexpected SecArgName (Position 1 6) "_"
+Error: [Cabal-7167]
+Error parsing project file dir-elif/elif.config:
+  imported by: elif.project
+
+dir-elif/elif.config:4:6: error:
+  unexpected SecArgName (Position 4 6) "_"
+      3 | if false
+      4 | elif _
+        |      ^
+
+
 # cabal v2-build
 Warnings found while parsing the project file, else.project:
- - dir-else/else.config: Unrecognized section '_' on line 3
+ - dir-else/else.config:3:5: Invalid subsection "_"
diff --git a/cabal-testsuite/PackageTests/ProjectImport/ParseErrorProvenance/cabal.test.hs b/cabal-testsuite/PackageTests/ProjectImport/ParseErrorProvenance/cabal.test.hs
index ca3bce1c59d..34d06d8f93a 100644
--- a/cabal-testsuite/PackageTests/ProjectImport/ParseErrorProvenance/cabal.test.hs
+++ b/cabal-testsuite/PackageTests/ProjectImport/ParseErrorProvenance/cabal.test.hs
@@ -9,20 +9,20 @@ main = cabalTest . recordMode RecordMarked $ do
 
 
   outDefault <- fails $ cabal' "v2-build" [ "all", "--dry-run", "--project-file=cabal.project" ]
-  assertOutputContains "Error parsing project file cabal.project:3" outDefault
+  assertOutputContains "cabal.project:3:4: error:" outDefault
   assertOutputDoesNotContain "imported by:" outDefault
 
   outIf <- fails $ cabal' "v2-build" [ "all", "--dry-run", "--project-file=if.project" ]
-  assertOutputContains (normalizeWindowsOutput "Error parsing project file dir-if/if.config:3") outIf
+  assertOutputContains (normalizeWindowsOutput "dir-if/if.config:3:4: error:") outIf
   assertOutputContains "imported by:" outIf
 
   outElif <- fails $ cabal' "v2-build" [ "all", "--dry-run", "--project-file=elif.project" ]
-  assertOutputContains (normalizeWindowsOutput "Error parsing project file dir-elif/elif.config:4") outElif
+  assertOutputContains (normalizeWindowsOutput "dir-elif/elif.config:4:6: error:") outElif
   assertOutputContains "imported by:" outElif
 
   outElse <- fails $ cabal' "v2-build" [ "all", "--dry-run", "--project-file=else.project" ]
   assertOutputContains "Warnings found while parsing the project file, else.project:" outElse
-  assertOutputContains (normalizeWindowsOutput "- dir-else/else.config: Unrecognized section '_' on line 3") outElse
+  assertOutputContains (normalizeWindowsOutput "- dir-else/else.config:3:5: Invalid subsection \"_\"") outElse
   assertOutputContains "When using configuration from:" outElse
 
   return ()
diff --git a/cabal-testsuite/PackageTests/ProjectImport/ParseWarningProvenance/cabal.out b/cabal-testsuite/PackageTests/ProjectImport/ParseWarningProvenance/cabal.out
index 90265370e7a..6fb7a1906b3 100644
--- a/cabal-testsuite/PackageTests/ProjectImport/ParseWarningProvenance/cabal.out
+++ b/cabal-testsuite/PackageTests/ProjectImport/ParseWarningProvenance/cabal.out
@@ -1,10 +1,10 @@
 # cabal v2-build
 Warnings found while parsing the project file, cabal.project:
-  - dir-x/a.config: Unrecognized section '-' on line 1
-  - dir-x/a.config: Unrecognized section '-' on line 2
-  - dir-x/a.config: Unrecognized section '-' on line 3
-  - dir-y/a.config: Unrecognized section '-' on line 123
-  - x.config: Unrecognized section '-' on line 1
-  - x.config: Unrecognized section '-' on line 2
-  - x.config: Unrecognized section '-' on line 3
-  - y.config: Unrecognized section '-' on line 123
+ - dir-x/a.config:1:1: Invalid subsection "-"
+ - dir-x/a.config:2:1: Invalid subsection "-"
+ - dir-x/a.config:3:1: Invalid subsection "-"
+ - dir-y/a.config:123:1: Invalid subsection "-"
+ - x.config:1:1: Invalid subsection "-"
+ - x.config:2:1: Invalid subsection "-"
+ - x.config:3:1: Invalid subsection "-"
+ - y.config:123:1: Invalid subsection "-"
diff --git a/cabal-testsuite/PackageTests/Regression/T5213/cabal.out b/cabal-testsuite/PackageTests/Regression/T5213/cabal.out
index fb0e7ad7a9a..bcbb8421e34 100644
--- a/cabal-testsuite/PackageTests/Regression/T5213/cabal.out
+++ b/cabal-testsuite/PackageTests/Regression/T5213/cabal.out
@@ -1,4 +1,6 @@
 # cabal new-test
+Warnings found while parsing the project file, cabal.project:
+ - cabal.project:4:3: The field "library-coverage" is deprecated in the Cabal specification version 1.22. Please use 'coverage' field instead.
 Resolving dependencies...
 Build profile: -w ghc-<GHCVER> -O1
 In order, the following will be built:
diff --git a/cabal-testsuite/PackageTests/Regression/T5213/cabal.project b/cabal-testsuite/PackageTests/Regression/T5213/cabal.project
index e1c33e00303..45f18c1f5cb 100644
--- a/cabal-testsuite/PackageTests/Regression/T5213/cabal.project
+++ b/cabal-testsuite/PackageTests/Regression/T5213/cabal.project
@@ -1,4 +1,4 @@
 packages: .
 
 package cabal-gh5213
-  library-coverage: true
+  library-coverage: True
diff --git a/cabal-validate/src/Main.hs b/cabal-validate/src/Main.hs
index bf5e30a26c2..a9ab2bc8db4 100644
--- a/cabal-validate/src/Main.hs
+++ b/cabal-validate/src/Main.hs
@@ -359,6 +359,14 @@ cliTests opts = do
         ++ tastyArgs opts
     )
 
+  timedCabalBin
+    opts
+    "cabal-install"
+    "test:parser-tests"
+    ( jobsArgs opts
+        ++ tastyArgs opts
+    )
+
   timedCabalBin
     opts
     "cabal-install"
diff --git a/cabal.validate.project b/cabal.validate.project
index 5075458c1b8..2fbc461042b 100644
--- a/cabal.validate.project
+++ b/cabal.validate.project
@@ -9,6 +9,8 @@ program-options
   ghc-options: -Werror
 
 -- if you are developing on a system without TH, use a `cabal.validate.project.local`
--- to disable this
+-- to disable the git-rev flag.
+-- The +legacy-comparision flag is to set the default project file parser to compare
+-- the result of the legacy and parsec parser and fail if they are not equal.
 package cabal-install
-  flags: +git-rev
+  flags: +git-rev +legacy-comparison
diff --git a/changelog.d/pr-8889 b/changelog.d/pr-8889
new file mode 100644
index 00000000000..0c3ec7ce79d
--- /dev/null
+++ b/changelog.d/pr-8889
@@ -0,0 +1,27 @@
+synopsis: Replace cabal project parsing with parsec parser
+packages: cabal-install Cabal Cabal-syntax
+prs: #8889
+issues: #6101 #7748
+significance: significant
+
+description: {
+
+Replaced the legacy cabal.project parser with a new implementation based on the same
+parsing infrastructure as cabal files.
+
+The new parser replicates the grammar of the legacy parser, ensuring that it generates identical `ProjectConfig` values.
+The implementation leverages existing Parsec infrastructure, including FieldGrammar and other utilities from the .cabal file parser.
+The error messages are now more accurate and include the line and column of the error.
+
+There is a new flag `--project-file-parser=<legacy|default|parsec|fallback|compare>` which can be used to select the parser to use.
+
+* `legacy` - the old parser
+* `default` - the default, by default the `fallback` strategy is used unless you have compiled `cabal-install` with `-f+legacy-comparison`.
+* `parsec` - the new parser using parsec
+* `fallback` - the new parser using parsec, but falling back to the old parser if it fails
+* `compare` - the new parser using parsec, but comparing the results with the old parser
+
+In the next release we plan to remove the legacy parser.
+
+
+}
diff --git a/doc/cabal-project-description-file.rst b/doc/cabal-project-description-file.rst
index 7b9bd5d5241..adae4514b14 100644
--- a/doc/cabal-project-description-file.rst
+++ b/doc/cabal-project-description-file.rst
@@ -413,6 +413,22 @@ package, and thus apply globally:
 
     This option can only be specified from the command line.
 
+.. _cmdoption-project-file-parser:
+.. option:: --project-file-parser=PARSER
+
+    :since: 3.18
+
+    Specifies the parser to use for reading the project file. The available
+    parsers are:
+
+    * ``legacy`` - the old parser (will be removed in a future release)
+    * ``default`` - the default parser (uses ``fallback`` unless compiled with ``-f+legacy-comparison``)
+    * ``parsec`` - the new parser using Parsec
+    * ``fallback`` - the new parser using Parsec, but falling back to the old parser if it fails
+    * ``compare`` - the new parser using Parsec, but comparing the results with the old parser
+
+    This option can only be specified from the command line.
+
 .. option:: -z, --ignore-project
 
     Ignores the local ``cabal.project`` file and uses the default
@@ -1824,7 +1840,7 @@ Advanced global configuration options
     ``--build-summary=TEMPLATE``.
 
 Undocumented fields: ``root-cmd``, ``symlink-bindir``, ``build-log``,
-``remote-build-reporting``, ``report-planned-failure``, ``offline``.
+``remote-build-reporting``, ``report-planning-failure``, ``offline``.
 
 Advanced solver options
 ^^^^^^^^^^^^^^^^^^^^^^^