fix: report special opt rule as warning instead of error

CHANGELOG.md

@@ -6,6 +6,10 @@
 
 Added `dfx canister snapshot download` and `dfx canister snapshot upload` commands to download and upload the canister snapshot.
 
+### fix: dfx now warns when encountering a special opt rule
+
+dfx now shows warnings when the new Candid declaration is a subtype of the old Candid declaration via a special opt rule, instead of throwing an error.
+
 # 0.28.0
 
 ### fix: deps deploy works with Canister ID out of the ranges of the pocket-ic subnets

e2e/tests-dfx/upgrade_check.bash

@@ -71,7 +71,7 @@ teardown() {
   jq '.canisters.hello_backend.main="v4_bad.mo"' dfx.json | sponge dfx.json
   echo yes | (
   assert_command dfx deploy
-  assert_match "Candid interface compatibility check failed"
+  assert_match "FIX ME! opt text <: opt int via special opt rule."
   )
   assert_command dfx canister call hello_backend f '()'
   assert_match "(opt \"\")"

src/dfx/src/lib/models/canister.rs

@@ -440,7 +440,7 @@ fn check_valid_subtype(compiled_idl_path: &Path, specified_idl_path: &Path) -> D
     let mut gamma = HashSet::new();
     let specified_type = env.merge_type(env2, specified_type);
     subtype_with_config(
-        OptReport::Error,
+        OptReport::Warning,
         &mut gamma,
         &env,
         &compiled_type,

src/dfx/src/lib/operations/canister/install_canister.rs

@@ -337,7 +337,7 @@ fn check_candid_compatibility(
         .ok_or_else(|| anyhow!("Deployed did file should contain some service interface"))?;
     let mut gamma = HashSet::new();
     let old_type = env.merge_type(env2, old_type);
-    let result = subtype_with_config(OptReport::Error, &mut gamma, &env, &new_type, &old_type);
+    let result = subtype_with_config(OptReport::Warning, &mut gamma, &env, &new_type, &old_type);
     Ok(match result {
         Ok(_) => None,
         Err(e) => Some(e.to_string()),