[paulb777]

Problem

FirestoreQueryObservable stores the closure returned by createListener(with:) in
self.setupListener, and that closure captured self strongly. The resulting cycle
(self → setupListener → self) means deinit, which calls removeListener(), never runs.
Every @FirestoreQuery therefore leaks its observable. The observable's snapshot listener stays
registered, and keeps receiving and reading documents, after the view that owned it is gone. The
snapshot handlers passed to createListener already capture self weakly, so this closure was
the only strong capture.

Change

Capture self weakly in the closure returned by createListener(with:) (2 lines). The closure
is only invoked through the observable (from its initializers and when configuration changes),
so the guard never fires while the observable is alive.

Testing

Added Firestore/Swift/Tests/Unit/PropertyWrapper/FirestoreQueryObservableLifetimeTests.swift.
It uses Swift Testing and is part of the FirebaseFirestoreTests SPM target. The tests swap
Query.addSnapshotListener(_:) for a fake that hands out recording ListenerRegistrations.
Each test drops the last strong reference to the observable, then checks that the observable is
deallocated and that its registration was removed. There are three cases:

• array results;
• Result results;
• array results after a configuration change has replaced the listener.

xcodebuild -scheme FirebaseFirestoreTests test -destination 'platform=macOS' \
  -only-testing:FirebaseFirestoreTests/FirestoreQueryObservableLifetimeTests
xcodebuild -scheme FirebaseFirestoreTests test -destination 'platform=macOS'

• Without the source change, all 3 new tests fail: the observable outlives its last reference,
  and removeCount == 0.
• With the change, the full scheme passes: 9 tests in 3 suites. It also passes 30 iterations in
  a row (-test-iterations 30 -run-tests-until-failure), 270/270.
• ./scripts/style.sh is clean.
• Unrelated to this change: under -test-iterations stress, "Stream handles (nil, nil) events
  gracefully" in AsyncSequenceTests.swift occasionally fails, even with the new suite skipped.
  Those suites aren't .serialized, and their tests swap the same method concurrently.

#16826 touches the same file on different lines (it merges cleanly). The two CHANGELOG entries
will need a trivial merge.

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[paulb777]

/gemini review

[gemini-code-assist]

Code Review

This pull request addresses a memory leak in @FirestoreQuery by capturing self weakly inside the listener creation closure. It also adds a comprehensive unit test suite to verify the lifetime and deallocation of FirestoreQueryObservable. The review feedback correctly points out a compilation error in the new test file where weak references are declared using let instead of var.

[paulb777]

[paulb777-bot] Requesting an automated review, as on the other PRs from this batch.

/gemini review

[gemini-code-assist]

Code Review

This pull request fixes a memory leak in @FirestoreQuery by capturing self weakly inside the listener creation closure in FirestoreQueryObservable.swift. It also adds comprehensive unit tests to verify the lifetime and deallocation behavior of the observable. The review comments correctly point out that weak references in the new tests must be declared as mutable variables (weak var) instead of constants (weak let) to avoid compiler errors.