[paulb777]

Summary

Store the observer handle returned by NotificationCenter in
listenerHandles, instead of the listener closure. Removing an auth state or
ID token listener now releases it, and deinit removes the observers that are
still registered.

Fixes #16938.

Why

addIDTokenDidChangeListener(_:) added the listener closure to
listenerHandles, but removeIDTokenDidChangeListener(_:),
removeStateDidChangeListener(_:), and deinit expect the handles returned by
NotificationCenter.addObserver(forName:object:queue:using:) there. A handle
never matched a closure, so:

• Removing a listener left its closure in listenerHandles. The listener, and
  everything it captured, stayed in memory for the lifetime of Auth, which
  for Auth.auth() is the life of the app. Apps that add and remove listeners
  repeatedly, for example one per screen or per subscription, accumulated them
  without bound.
• deinit passed the closures to removeObserver(_:), which did nothing, so
  the observers of a deallocated Auth stayed registered with
  NotificationCenter, along with their listeners.

addStateDidChangeListener(_:) is built on addIDTokenDidChangeListener(_:),
and the authStateChanges and idTokenChanges sequences and the Combine
publishers use these methods, so all of them were affected. The Objective-C SDK
stored the handle. This regressed in the Swift port (#11237), and has been
present since 11.0.0.

Changes

• addIDTokenDidChangeListener(_:) adds the observer handle to
  listenerHandles, like the Objective-C SDK did.
• listenerHandles is now [NSObjectProtocol] instead of NSMutableArray, so
  the compiler rejects adding anything other than an observer handle, such as
  the closure. The remove methods remove the handle by identity, and deinit
  removes each remaining observer from NotificationCenter.
• deinit also removes the didBecomeActiveNotification and
  didEnterBackgroundNotification observers on tvOS, where
  getToken(forcingRefresh:completion:) adds them too. Before, it only removed
  them on iOS (from review).
• CHANGELOG entry.

Notes for reviewers

• Matching: NSMutableArray.remove(_:) matched with isEqual:. The
  handles are __NSObserver instances, which don't override isEqual:, so
  matching by identity (===) finds the same handles.
• Locking: add and remove still change the array while holding the
  Auth.self lock, and now release it with defer, like
  removeStateDidChangeListener(_:) (from review). In
  addIDTokenDidChangeListener(_:), the defer is in a do block, so the lock
  isn't held while the initial call is dispatched. deinit doesn't take the
  lock, as before, since it only runs when nothing else holds the instance.
• Initial call: a listener that is removed before its initial call runs is
  still called once, and is released after that. The Objective-C SDK behaved
  the same way. Not changed here.

Testing

• New tests in AuthTests, which check through a weak reference that an object
  captured by a listener is deallocated:
  • testRemoveStateDidChangeListenerReleasesListener and
    testRemoveIDTokenDidChangeListenerReleasesListener add a listener, remove
    it, and let the initial call run.
  • testDeallocatingAuthRemovesListeners adds both kinds of listener to a new
    Auth, and lets it deallocate without removing them. It also checks that
    the Auth instance is deallocated.
• Check that the tests catch the bug: on main, all three fail. In
  testDeallocatingAuthRemovesListeners, the Auth instance is deallocated,
  but the captured object isn't, because NotificationCenter still holds the
  observer.
• xcodebuild -scheme AuthUnit -destination 'platform=iOS Simulator,name=iPhone 17 Pro,OS=26.5' test: 403 tests, 0 failures.
• xcodebuild -scheme AuthUnit -destination 'platform=tvOS Simulator,name=Apple TV 4K (3rd generation),OS=26.5' test: 296 tests, 0 failures.
• The three new tests passed 200 times in a row (-test-iterations 200).

Related

Noted under "Not included" in #16856.

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[paulb777]

/gemini review

[gemini-code-assist]

Code Review

This pull request resolves a memory leak in FirebaseAuth where removed auth state and ID token listeners, along with their captured objects, were retained in memory. The fix transitions listenerHandles from NSMutableArray to a Swift array of [NSObjectProtocol], simplifying the addition, removal, and deinitialization cleanup. Additionally, new unit tests are introduced to verify that listeners are correctly released. The review feedback suggests extending the platform check in deinit to include tvOS to prevent observer leaks on that platform as well.

[paulb777]

/gemini review

[gemini-code-assist]

Code Review

This pull request resolves a memory leak in FirebaseAuth by migrating listenerHandles from NSMutableArray to a native Swift array of [NSObjectProtocol]. This allows proper cleanup of auth state and ID token listeners, ensuring they and their captured objects are released when removed or when the Auth instance is deallocated. Additionally, new unit tests have been added to verify this behavior. The review feedback suggests improving safety and consistency by using defer { objc_sync_exit(Auth.self) } immediately after entering synchronized blocks in addIDTokenDidChangeListener and removeIDTokenDidChangeListener.