fix: TeeHandler should call Handler on a dependent handler only if it is enabled for the given record

On closer inspection, `Handler.Handle()` should only be called if the `Handler` is enabled for the given record. This fixes that for the `TeeHandler` checking this for each dependent handler.

Note, the implementation of `Enabled` is still valid, and prevents `Handle` from even being called in cases where no dependent handler is enabled for the given record.

This fix is important as without it, all logs end up in the error log file.

Author: arthurpitman

internal/log/tee_handler.go

@@ -59,7 +59,9 @@ func (t *TeeHandler) Handle(ctx context.Context, r slog.Record) error {
 
 	errs := []error{}
 	for _, h := range t.handlers {
-		errs = append(errs, h.Handle(ctx, r))
+		if h.Enabled(ctx, r.Level) {
+			errs = append(errs, h.Handle(ctx, r))
+		}
 	}
 	return errors.Join(errs...)
 }

internal/log/tee_handler_test.go

@@ -104,6 +104,30 @@ func TestTeeHandler_Handle(t *testing.T) {
 		assert.Contains(t, handler2.Output.String(), "level=WARN msg=test key=value")
 	})
 
+	t.Run("handlers with different log levels handle correctly", func(t *testing.T) {
+		allLevelsHandler := NewTestHandler(&slog.HandlerOptions{})
+		errorLevelHandler := NewTestHandler(&slog.HandlerOptions{Level: slog.LevelError})
+
+		testingHandler := log.NewTeeHandler(allLevelsHandler, errorLevelHandler)
+
+		err := testingHandler.Handle(t.Context(), slog.Record{
+			Level:   slog.LevelInfo,
+			Message: "info message",
+		})
+		require.NoError(t, err)
+
+		err = testingHandler.Handle(t.Context(), slog.Record{
+			Level:   slog.LevelError,
+			Message: "error message",
+		})
+		require.NoError(t, err)
+
+		assert.Contains(t, allLevelsHandler.Output.String(), "info message")
+		assert.NotContains(t, errorLevelHandler.Output.String(), "info message")
+		assert.Contains(t, allLevelsHandler.Output.String(), "error message")
+		assert.Contains(t, errorLevelHandler.Output.String(), "error message")
+	})
+
 }
 
 // TestTeeHandler_WithAttrs tests that a TeeHandler is returned that applies the given attributes to each handled record.