feat(cubit): optional StateError when emit happens

[maRci002]

Status

READY

Breaking Changes

NO

Description

This PR focuses on Local Cubits where the cubit might become closed / disposed during processing async Cubit functions.

Current problem and workarounds:

class SomeCubit extends Cubit<int> {
  SomeCubit() : super(0);

  Future<void> test() async {
    try {
      emit(1);
      await Future.delayed(const Duration(seconds: 5));
      // if user leaves the page / dialog E.g. `pushReplacementNamed` then cubit is already closed
      // check `isClosed` every time after a future completes?
      if (!isClosed) {
        emit(2);
      }
    } on StateError {
      // here we could ignore StateError('Cannot emit new states after calling close')
      // but this seems overkill for every single cubit function
    }
  }
}

Syntax if programmer knows the Cubit is a local cubit / temporary cubit:

SomeCubit() : super(0, emitFailsWhenClosed: false)

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore

closes #2980

[maRci002]

I'm sorry I need to do a little refactor since bloc already awaits ongoing event emitters.

In addition, if [close] is called while events are still being processed, the [Bloc] will finish processing the pending events.

However Cubit doesn't have this feature so I'm going to apply the changes only for it.

[maRci002]

@felangel will you please review this PR?

Maybe Cubit should give explicit emitFailsWhenClosed: false to his base contructor (so all Cubits are safe) or BlocBase should mark bool get emitFailsWhenClosed accessor as abstract.
Or just completly refactor Cubit's logic for instance keep track of async Cubit functions.

[felangel]

@felangel will you please review this PR?

Maybe Cubit should give explicit emitFailsWhenClosed: false to his base contructor (so all Cubits are safe) or BlocBase should mark bool get emitFailsWhenClosed accessor as abstract. Or just completly refactor Cubit's logic for instance keep track of async Cubit functions.

I'd prefer to hold off on this change for a little bit and evaluate other potential solutions. I want to make sure we carefully consider all options/approaches to resolve this before adding a new public API. Really appreciate you taking the time to create this PR 👍

I'll think about it a bit more over the next few days and get back to you, thanks! 🙏

[felangel]

@maRci002 I'd love your thoughts on #3069, thanks! 🙏

[felangel]

Closing this for now since we need to discuss/align on an approach first (#3069)