fix(bloc): omit synthetic BlocBase.addError frame from auto-captured stack traces

packages/bloc/CHANGELOG.md

@@ -1,3 +1,7 @@
+# 9.3.0
+
+- fix: omit synthetic `BlocBase.addError` frame from stack traces auto-captured when no `stackTrace` is passed to `addError` ([#3585](https://github.com/felangel/bloc/issues/3585))
+
 # 9.2.0
 
 - feat: add `MultiBlocObserver` ([#4714](https://github.com/felangel/bloc/pull/4714))

packages/bloc/lib/src/bloc_base.dart

@@ -138,11 +138,15 @@ abstract class BlocBase<State>
   }
 
   /// Reports an [error] which triggers [onError] with an optional [StackTrace].
+  ///
+  /// If no [stackTrace] is provided, the current stack trace is captured with
+  /// the synthetic `BlocBase.addError` frame stripped, so the resulting trace
+  /// begins at the caller's call site.
   @protected
   @mustCallSuper
   @override
   void addError(Object error, [StackTrace? stackTrace]) {
-    onError(error, stackTrace ?? StackTrace.current);
+    onError(error, stackTrace ?? _withoutTopFrame(StackTrace.current));
   }
 
   /// Called whenever an [error] occurs and notifies [BlocObserver.onError].
@@ -175,4 +179,11 @@ abstract class BlocBase<State>
     _blocObserver.onClose(this);
     await _stateController.close();
   }
+
+  static StackTrace _withoutTopFrame(StackTrace trace) {
+    final raw = trace.toString();
+    final newline = raw.indexOf('\n');
+    if (newline < 0) return trace;
+    return StackTrace.fromString(raw.substring(newline + 1));
+  }
 }

packages/bloc/pubspec.yaml

@@ -1,6 +1,6 @@
 name: bloc
 description: A predictable state management library that helps implement the BLoC (Business Logic Component) design pattern.
-version: 9.2.0
+version: 9.3.0
 repository: https://github.com/felangel/bloc/tree/master/packages/bloc
 issue_tracker: https://github.com/felangel/bloc/issues
 homepage: https://github.com/felangel/bloc

packages/bloc/test/cubit_test.dart

@@ -66,6 +66,43 @@ void main() {
           () => observer.onError(cubit, expectedError, expectedStackTrace),
         ).called(1);
       });
+
+      test('omits BlocBase.addError frame when no stackTrace is passed',
+          () async {
+        StackTrace? captured;
+        CounterCubit(
+          onErrorCallback: (_, stackTrace) => captured = stackTrace,
+          // ignore: invalid_use_of_protected_member
+        ).addError(Exception('fatal exception'));
+
+        expect(captured, isNotNull);
+        final firstLine = captured!.toString().split('\n').first;
+        expect(firstLine, isNot(contains('BlocBase.addError')));
+        expect(firstLine, isNot(contains('bloc_base.dart')));
+      });
+
+      test('passes through an explicit stackTrace unchanged', () async {
+        final explicit = StackTrace.fromString('#0 user_call (test.dart:1)');
+        StackTrace? captured;
+        CounterCubit(
+          onErrorCallback: (_, stackTrace) => captured = stackTrace,
+          // ignore: invalid_use_of_protected_member
+        ).addError(Exception('fatal exception'), explicit);
+
+        expect(captured, same(explicit));
+      });
+
+      test('captured stackTrace is non-empty when no stackTrace is passed',
+          () async {
+        StackTrace? captured;
+        CounterCubit(
+          onErrorCallback: (_, stackTrace) => captured = stackTrace,
+          // ignore: invalid_use_of_protected_member
+        ).addError(Exception('fatal exception'));
+
+        expect(captured, isNotNull);
+        expect(captured!.toString(), isNotEmpty);
+      });
     });
 
     group('onChange', () {