fix(auth, functions): Xcode 26.4 'async let' cleanup crashes (#15991)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: ncooke3

FirebaseAuth/CHANGELOG.md

@@ -3,6 +3,9 @@
   `Auth.idTokenChanges`, providing a modern, structured-concurrency
   alternative to `addStateDidChangeListener` and `addIDTokenDidChangeListener`.
 - [fixed] Fix a race condition with User.providerData getter. (#15950)
+- [fixed] Fixed a release-build crash in networking code when using
+  Xcode 26.4 (Swift 6.3) that was caused by a Swift regression in `async let`
+  teardown. (#15974)
 
 # 12.9.0
 - [fixed] Stop doing unnecessary AppCheck token refreshes. Introduced

FirebaseAuth/Sources/Swift/Backend/AuthBackend.swift

@@ -64,38 +64,53 @@ final class AuthBackend: AuthBackendProtocol {
                       httpMethod: String,
                       contentType: String,
                       requestConfiguration: AuthRequestConfiguration) async -> URLRequest {
+    // Previously, this section used `async let`, but that was changed for a
+    // `Task`-based approach to work around a Swift 6.3 regression in Xcode 26.4.
+    // - Context: https://github.com/firebase/firebase-ios-sdk/issues/15974
     // Kick off tasks for the async header values.
-    async let heartbeatsHeaderValue = requestConfiguration.heartbeatLogger?.asyncHeaderValue()
-    async let appCheckTokenHeaderValue = requestConfiguration.appCheck?
-      .getToken(forcingRefresh: false)
-
-    var request = URLRequest(url: url)
-    request.setValue(contentType, forHTTPHeaderField: "Content-Type")
-    let additionalFrameworkMarker = requestConfiguration.additionalFrameworkMarker
-    let clientVersion = "iOS/FirebaseSDK/\(FirebaseVersion())/\(additionalFrameworkMarker)"
-    request.setValue(clientVersion, forHTTPHeaderField: "X-Client-Version")
-    request.setValue(Bundle.main.bundleIdentifier, forHTTPHeaderField: "X-Ios-Bundle-Identifier")
-    request.setValue(requestConfiguration.appID, forHTTPHeaderField: "X-Firebase-GMPID")
-    request.httpMethod = httpMethod
-    let preferredLocalizations = Bundle.main.preferredLocalizations
-    if preferredLocalizations.count > 0 {
-      request.setValue(preferredLocalizations.first, forHTTPHeaderField: "Accept-Language")
+    let heartbeatsHeaderValue = Task {
+      await requestConfiguration.heartbeatLogger?.asyncHeaderValue()
     }
-    if let languageCode = requestConfiguration.languageCode,
-       languageCode.count > 0 {
-      request.setValue(languageCode, forHTTPHeaderField: "X-Firebase-Locale")
+    let appCheckTokenHeaderValue = Task {
+      await requestConfiguration.appCheck?.getToken(forcingRefresh: false)
     }
-    // Wait for the async header values.
-    await request.setValue(heartbeatsHeaderValue, forHTTPHeaderField: "X-Firebase-Client")
-    if let tokenResult = await appCheckTokenHeaderValue {
-      if let error = tokenResult.error {
-        AuthLog.logWarning(code: "I-AUT000018",
-                           message: "Error getting App Check token; using placeholder " +
-                             "token instead. Error: \(error)")
+
+    return await withTaskCancellationHandler {
+      defer {
+        heartbeatsHeaderValue.cancel()
+        appCheckTokenHeaderValue.cancel()
+      }
+      var request = URLRequest(url: url)
+      request.setValue(contentType, forHTTPHeaderField: "Content-Type")
+      let additionalFrameworkMarker = requestConfiguration.additionalFrameworkMarker
+      let clientVersion = "iOS/FirebaseSDK/\(FirebaseVersion())/\(additionalFrameworkMarker)"
+      request.setValue(clientVersion, forHTTPHeaderField: "X-Client-Version")
+      request.setValue(Bundle.main.bundleIdentifier, forHTTPHeaderField: "X-Ios-Bundle-Identifier")
+      request.setValue(requestConfiguration.appID, forHTTPHeaderField: "X-Firebase-GMPID")
+      request.httpMethod = httpMethod
+      let preferredLocalizations = Bundle.main.preferredLocalizations
+      if preferredLocalizations.count > 0 {
+        request.setValue(preferredLocalizations.first, forHTTPHeaderField: "Accept-Language")
+      }
+      if let languageCode = requestConfiguration.languageCode,
+         languageCode.count > 0 {
+        request.setValue(languageCode, forHTTPHeaderField: "X-Firebase-Locale")
+      }
+      // Wait for the async header values.
+      await request.setValue(heartbeatsHeaderValue.value, forHTTPHeaderField: "X-Firebase-Client")
+      if let tokenResult = await appCheckTokenHeaderValue.value {
+        if let error = tokenResult.error {
+          AuthLog.logWarning(code: "I-AUT000018",
+                             message: "Error getting App Check token; using placeholder " +
+                               "token instead. Error: \(error)")
+        }
+        request.setValue(tokenResult.token, forHTTPHeaderField: "X-Firebase-AppCheck")
       }
-      request.setValue(tokenResult.token, forHTTPHeaderField: "X-Firebase-AppCheck")
+      return request
+    } onCancel: {
+      heartbeatsHeaderValue.cancel()
+      appCheckTokenHeaderValue.cancel()
     }
-    return request
   }
 
   private static func generateMFAError(response: AuthRPCResponse, auth: Auth) -> Error? {

FirebaseFunctions/CHANGELOG.md

@@ -1,3 +1,8 @@
+# Unreleased
+- [fixed] Fixed a release-build crash in `HTTPSCallable.call()` when using
+  Xcode 26.4 (Swift 6.3) that was caused by a Swift regression in `async let`
+  teardown. (#15974)
+
 # 12.0.0
 - [changed] **Breaking Change**: Mark `HTTPSCallable` and `HTTPSCallableOptions`
   as `final` classes for Swift clients. This was to achieve Swift 6 checked

FirebaseFunctions/Sources/Internal/FunctionsContext.swift

@@ -37,18 +37,32 @@ struct FunctionsContextProvider: Sendable {
   }
 
   func context(options: HTTPSCallableOptions?) async throws -> FunctionsContext {
-    async let authToken = auth?.getToken(forcingRefresh: false)
-    async let appCheckToken = getAppCheckToken(options: options)
-    async let limitedUseAppCheckToken = getLimitedUseAppCheckToken(options: options)
+    // Previously, this section used `async let`, but that was changed for a
+    // `Task`-based approach to work around a Swift 6.3 regression in Xcode 26.4.
+    // - Context: https://github.com/firebase/firebase-ios-sdk/issues/15974
+    let authToken = Task { try await auth?.getToken(forcingRefresh: false) }
+    let appCheckToken = Task { await getAppCheckToken(options: options) }
+    let limitedUseAppCheckToken = Task { await getLimitedUseAppCheckToken(options: options) }
 
-    // Only `authToken` is throwing, but the formatter script removes the `try`
-    // from `try authToken` and puts it in front of the initializer call.
-    return try await FunctionsContext(
-      authToken: authToken,
-      fcmToken: messaging?.fcmToken,
-      appCheckToken: appCheckToken,
-      limitedUseAppCheckToken: limitedUseAppCheckToken
-    )
+    return try await withTaskCancellationHandler {
+      defer {
+        authToken.cancel()
+        appCheckToken.cancel()
+        limitedUseAppCheckToken.cancel()
+      }
+      // Only `authToken` is throwing, but the formatter script removes the `try`
+      // from `try authToken` and puts it in front of the initializer call.
+      return try await FunctionsContext(
+        authToken: authToken.value,
+        fcmToken: messaging?.fcmToken,
+        appCheckToken: appCheckToken.value,
+        limitedUseAppCheckToken: limitedUseAppCheckToken.value
+      )
+    } onCancel: {
+      authToken.cancel()
+      appCheckToken.cancel()
+      limitedUseAppCheckToken.cancel()
+    }
   }
 
   private func getAppCheckToken(options: HTTPSCallableOptions?) async -> String? {