fix(auth, functions): Xcode 26.4 'async let' cleanup crashes by ncooke3 · Pull Request #15991 · firebase/firebase-ios-sdk

ncooke3 · 2026-03-26T19:30:47Z

Tip

Recommend to review without whitespace changes: https://github.com/firebase/firebase-ios-sdk/pull/15991/changes?w=1

Local emulator testing

Test Case '-[FirebaseFunctionsIntegration.IntegrationTests testUnknownErrorAsync]' passed (0.012 seconds).
Test Suite 'IntegrationTests' passed at 2026-03-31 17:10:54.699.
	 Executed 51 tests, with 0 failures (0 unexpected) in 7.407 (7.425) seconds
Test Suite 'FirebaseFunctionsIntegration.xctest' passed at 2026-03-31 17:10:54.700.
	 Executed 51 tests, with 0 failures (0 unexpected) in 7.407 (7.425) seconds
Test Suite 'All tests' passed at 2026-03-31 17:10:54.700.
	 Executed 51 tests, with 0 failures (0 unexpected) in 7.407 (7.426) seconds
2026-03-31 17:10:54.984 xcodebuild[91020:874036] [MT] IDETestOperationsObserverDebug: 9.900 elapsed -- Testing started completed.
2026-03-31 17:10:54.984 xcodebuild[91020:874036] [MT] IDETestOperationsObserverDebug: 0.000 sec, +0.000 sec -- start
2026-03-31 17:10:54.984 xcodebuild[91020:874036] [MT] IDETestOperationsObserverDebug: 9.900 sec, +9.900 sec -- end

Test session results, code coverage, and logs:
	/Users/nickcooke/Library/Developer/Xcode/DerivedData/firebase-ios-sdk-anxqgakbhyqozfhbkutiwmcpphvm/Logs/Test/Test-FirebaseFunctionsIntegration-2026.03.31_17-10-35--0400.xcresult

** TEST SUCCEEDED **

nickcooke@nickcooke-mac2 firebase-ios-sdk (nc/fix-15974) % git pull origin nc/fix-15974
From github.com:firebase/firebase-ios-sdk
 * branch                nc/fix-15974 -> FETCH_HEAD
Already up to date.
nickcooke@nickcooke-mac2 firebase-ios-sdk (nc/fix-15974) % xcode-select -p
/Applications/Xcode_26.4.app/Contents/Developer

Fix #15974

gemini-code-assist · 2026-03-26T19:30:51Z

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ncooke3 · 2026-03-26T21:05:29Z

/gemini review

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Code Review

This pull request replaces async let usage with explicit Task blocks in FirebaseAuth and FirebaseFunctions to work around a Swift 6.3 regression in Xcode 26.4 that causes release-build crashes during async let teardown. While the implementation correctly addresses the regression, a critical issue was identified in FunctionsContext.swift where the try keyword is misplaced before a non-throwing initializer; it should instead specifically precede the throwing expression await authToken.value to ensure successful compilation and correct error handling.

FirebaseFunctions/Sources/Internal/FunctionsContext.swift

ncooke3 · 2026-03-26T21:07:52Z

/gemini review

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Code Review

This pull request replaces async let with unstructured Task blocks in FirebaseAuth and FirebaseFunctions to work around a Swift 6.3 regression in Xcode 26.4 that causes release-build crashes. The review feedback highlights that this change results in the loss of automatic task cancellation propagation and suggests using withTaskCancellationHandler to restore the original behavior and improve the robustness of the workaround.

FirebaseAuth/Sources/Swift/Backend/AuthBackend.swift

FirebaseFunctions/Sources/Internal/FunctionsContext.swift

Swift 6.3 compiler regression (swiftlang/swift#87481) generates incorrect LIFO deallocation ordering for async-let stack frames. This causes swift_task_dealloc crashes in Release builds on physical iOS devices. Replace `async let` bindings with explicit `Task {}` objects in: - FunctionsContext.swift (3 bindings → 3 Tasks) - AuthBackend.swift (2 bindings → 2 Tasks) Matches firebase/firebase-ios-sdk PR firebase#15991 targeting 12.12.0. Temporary fork patch until upstream fix ships. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

…wiftlang/swift#87481) Backport of firebase#15991 to 12.11.0. Fixes SIGABRT: freed pointer was not the last allocation in release builds. Changes: - FunctionsContext.swift: 3 async let -> Task {} + .value - AuthBackend.swift: 2 async let -> Task {} + .value

ncooke3 · 2026-03-31T20:02:16Z

/gemini review

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Code Review

This pull request replaces the use of async let with a Task-based approach and withTaskCancellationHandler in both FirebaseAuth and FirebaseFunctions to mitigate a Swift regression causing crashes during teardown. The review feedback identifies an invalid await try syntax that needs to be corrected to try await and points out several version number typos (Xcode 26.4 and Swift 6.3) in the comments and changelogs that should be updated to reflect the correct versions.

FirebaseFunctions/Sources/Internal/FunctionsContext.swift

FirebaseAuth/CHANGELOG.md

ncooke3 · 2026-03-31T20:06:49Z

/gemini review

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Code Review

This pull request replaces async let with explicit Task management and withTaskCancellationHandler in FirebaseAuth and FirebaseFunctions to resolve a crash occurring with Xcode 16.4. The review feedback identifies several version number typos in the changelogs and source code comments that need correction. Additionally, an improvement was suggested for FunctionsContext.swift to use a defer block within the task handler to ensure that background tasks are properly cancelled if an error is thrown during execution, preventing potential resource leaks.

FirebaseFunctions/Sources/Internal/FunctionsContext.swift

FirebaseAuth/CHANGELOG.md

FirebaseAuth/Sources/Swift/Backend/AuthBackend.swift

FirebaseFunctions/CHANGELOG.md

FirebaseFunctions/Sources/Internal/FunctionsContext.swift

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ncooke3 · 2026-03-31T20:21:56Z

/gemini review

ncooke3 · 2026-03-31T20:23:13Z

FirebaseFunctions/Sources/Internal/FunctionsContext.swift

Since authToken.value can throw, an error will cause the operation block to exit early. Unlike async let, unstructured Tasks are not automatically cancelled when they go out of scope. This could lead to appCheckToken and limitedUseAppCheckToken continuing to run in the background if authToken fails.

Adding a defer block to cancel the tasks ensures they are cleaned up regardless of whether the function succeeds or throws.

Also, a task can be canceled more than once with no ill effects.

Sources:

https://docs.swift.org/swift-book/documentation/the-swift-programming-language/errorhandling/#Specifying-Cleanup-Actions

https://developer.apple.com/documentation/swift/task/cancel()

gemini-code-assist

Code Review

This pull request replaces the use of async let with explicit Task objects and withTaskCancellationHandler in FirebaseAuth and FirebaseFunctions to work around a Swift 6.0 regression in Xcode 16.2 that caused crashes during teardown in release builds. The feedback identifies several typos in the CHANGELOG files and source code comments where the Xcode and Swift versions were incorrectly listed as 26.4 and 6.3, respectively, and provides suggestions to correct them to 16.2 and 6.0.

FirebaseAuth/CHANGELOG.md

FirebaseAuth/Sources/Swift/Backend/AuthBackend.swift

FirebaseFunctions/CHANGELOG.md

FirebaseFunctions/Sources/Internal/FunctionsContext.swift

FirebaseAuth/Sources/Swift/Backend/AuthBackend.swift

FirebaseFunctions/Sources/Internal/FunctionsContext.swift

ncooke3 · 2026-03-31T20:25:58Z

/gemini review

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Code Review

This pull request replaces async let with explicit Task management and withTaskCancellationHandler in AuthBackend.swift and FunctionsContext.swift to resolve a release-build crash caused by a Swift compiler regression. The review feedback identifies typos in the Xcode and Swift version numbers cited in the CHANGELOGs and source code. Additionally, a code suggestion was provided to use a defer block in AuthBackend.swift to ensure tasks are cancelled, maintaining consistency with other implementations in the PR.

FirebaseAuth/Sources/Swift/Backend/AuthBackend.swift

FirebaseFunctions/CHANGELOG.md

FirebaseFunctions/Sources/Internal/FunctionsContext.swift

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ncooke3 · 2026-03-31T20:33:32Z

/gemini review

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Code Review

This pull request addresses a release-build crash occurring in Xcode 26.4 (Swift 6.3) caused by a regression in async let teardown. The fix replaces async let with explicit Task instances and withTaskCancellationHandler in both FirebaseAuth and FirebaseFunctions to ensure proper resource cleanup. Review feedback suggests minor refinements for clarity, including moving the await keyword closer to the asynchronous property access in AuthBackend.swift and updating an outdated comment regarding error handling in FunctionsContext.swift.

FirebaseAuth/Sources/Swift/Backend/AuthBackend.swift

FirebaseFunctions/Sources/Internal/FunctionsContext.swift

ncooke3 · 2026-04-01T01:00:58Z

Hi @mikehardy, fwiw, I couldn't reproduce the issue with Auth. For one, the async lets used it are for async ObjC APIs. Perhaps the interop layer triggers a different compiler reaction? So, I tried to wrap these calls in Swift methods (much like Functions does). Still couldn't reproduce the crash. I did pin it down to the 2 AppCheck related async lets in Functions. Disable either and Functions works, even with the async let for the Auth token call.

In any case, this "fix" shouldn't hurt Auth and I've decided to check it in anyhow to be preventative.

mikehardy · 2026-04-01T02:11:25Z

Interesting - thanks for the note there @ncooke3 , I reworded my placeholder issue over in react-native-firebase-land - hopefully doesn't affect too many folks before your workaround here makes it to release, it's been strangely quiet over there whereas I was expecting it to be a hot topic, so seems like your fix here is still out in front of most people's release build pipelines

ncooke3 added 4 commits March 26, 2026 15:19

fix: Xcode 26.4 'async let' cleanup crashes

18f89a2

changelog

ae4c475

Fix Functions comment

1cf0aeb

Corresponding fix in FirebaseAuth

4671342

ncooke3 added this to the 12.12.0 - M179 milestone Mar 26, 2026

danger-firebase-ios bot added api: auth api: functions labels Mar 26, 2026

ncooke3 mentioned this pull request Mar 26, 2026

[Functions] Release build crash in HTTPSCallable.call() due to Swift 6.3 async let compiler bug #15974

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ncooke3 and others added 2 commits March 27, 2026 12:05

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Merge branch 'main' into nc/fix-15974

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gotnull mentioned this pull request Mar 30, 2026

cloud_functions iOS crash (SIGABRT / libswift_Concurrency) when calling httpsCallable on physical device in profile/release mode (works in debug) firebase/flutterfire#18153

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ncooke3 and others added 2 commits March 31, 2026 16:09

Update FirebaseAuth/Sources/Swift/Backend/AuthBackend.swift

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mikehardy mentioned this pull request Mar 31, 2026

Crash in Functions in release mode, Xcode 26.4 only - workaround provided invertase/react-native-firebase#8949

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ncooke3 merged commit db5828b into main Apr 1, 2026
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ncooke3 deleted the nc/fix-15974 branch April 1, 2026 00:57

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