iOS Release crash: Swift 6.1 async let teardown bug in FirebaseFunctions/FirebaseStorage #75

Summary

iOS Release/Profile builds crash with SIGABRT (_swift_task_dealloc_specific / freed pointer was not the last allocation) on cooperative queue threads whenever code calls FirebaseFunctions.httpsCallable.call() or FirebaseStorage.ref.putData(). Debug builds are unaffected.

Root Cause

Swift 6.1 compiler bug — the optimizer generates incorrect LIFO teardown ordering for async let task allocations.

Exposed by flutterfire#18054 (feat(ios): migrate iOS to UIScene lifecycle), which shipped new Swift async code in:

• cloud_functions 6.0.7 → 6.1.0
• firebase_storage 13.1.0 → 13.2.0

Upstream Tracking

Current Workaround

Podfile post_install disables Swift optimization for the affected pods only:

if ['FirebaseFunctions', 'FirebaseStorage'].include?(target.name)
  target.build_configurations.each do |config|
    if config.name != 'Debug'
      config.build_settings['SWIFT_OPTIMIZATION_LEVEL'] = '-Onone'
    end
  end
end

Resolution Criteria

Remove the Podfile workaround once any of:

1. Swift compiler fix (swiftlang/swift#87571) ships in an Xcode update
2. FlutterFire releases patched cloud_functions / firebase_storage versions
3. Firebase iOS SDK adds its own workaround

Affected Versions

• Build 139 (1.24.0+139)
• Xcode 26.4, Swift 6.1, iOS 26.4
• Physical devices only (simulator uses macOS Swift runtime)