fix(bloc_concurrency): close droppable stream when source ends mid-event

[tonytonycoder11]

Status

READY

Breaking Changes

NO

Description

droppable() uses a hand-written _ExhaustMapStreamTransformer whose output StreamController is never closed when the source event stream completes while a mapped event handler is still in flight.

• The source onDone (() => mappedSubscription ?? controller.close()) intentionally defers closing while a mapped subscription is active, but
• the mapped subscription's onDone (() => mappedSubscription = null) only clears the reference and never re-checks whether the source has already completed.

As a result the transformed stream never emits done: the subscription leaks and a Bloc/Cubit that is closed while a droppable event is being processed never completes. The sibling transformers all propagate source completion (sequential → asyncExpand, concurrent → concurrentAsyncExpand, restartable → switchMap), so droppable was the only outlier.

This tracks source completion with an isSourceDone flag and closes the output controller once the source is done and no event is in flight (extracted into a small maybeClose() helper so the completion condition lives in one place):

• source completes while idle → close immediately (unchanged behavior);
• source completes while an event is in flight → close once the mapped subscription's onDone fires.

There is no public API change and no change to event-dropping, cancellation, or idle-completion behavior. A regression test covering the source-completes-mid-event path is included (it fails on master and passes with this change); the existing suite stays green at 100% coverage.

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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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