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

[gotnull]

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

Issue	Status
swiftlang/swift#81771	Swift compiler bug report
swiftlang/swift#87571	Fix PR (not yet merged)
flutterfire#18153	FlutterFire tracking issue
Swift Forums discussion	Community discussion

Current Workaround

Version pinning in pubspec.yaml to pre-UIScene migration versions:

firebase_storage: 13.1.0  # 13.2.0 triggers Swift 6.1 SIGABRT
cloud_functions: 6.0.7    # 6.1.0 triggers Swift 6.1 SIGABRT

This avoids the problematic native Swift async code entirely - no Podfile hacks, no -Onone overrides, no performance penalty.

Previously attempted workarounds (not recommended)

• Podfile -Onone: Fragile, disables Swift optimization for entire pods, hard to know which pods to cover.
• Pure Dart HTTP REST bypass: Works but loses native SDK benefits (retries, App Check, offline queueing).

Resolution Criteria

Unpin to ^ versions 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)

[gotnull]

Update: The Podfile -Onone workaround has been replaced with version pinning - a cleaner approach with no performance penalty:

firebase_storage: 13.1.0  # 13.2.0 triggers Swift 6.1 SIGABRT
cloud_functions: 6.0.7    # 6.1.0 triggers Swift 6.1 SIGABRT

These are the last versions before the UIScene lifecycle migration (flutterfire#18054) that introduced the Swift async patterns triggering the compiler bug. Pinning avoids the problematic native code entirely - all Firebase features work normally, no Podfile hacks needed.

Also reported firebase_storage 13.2.0 as affected on flutterfire#18153 (upstream was only tracking cloud_functions).