[StoreKit2] Fix Xcode 15 dyld launch crashes on iOS <=16 and update documentation

This commit resolves several known compiler and runtime issues when compiling C++ alongside modern Swift (Concurrency) using Xcode 15+ for deployment on iOS 15/16:

1. `swift_task_alloc` (EXC_BAD_ACCESS): Mixing Swift Concurrency with `@objc` interfaces and C++ pointers on older runtimes causes memory segmentation faults. We introduced an Objective-C++ Block Barrier to keep C pointers on the C++ side (`analytics_ios.mm`) and used a detached `Task` with a pure Swift struct (`AppleTransactionVerifier.swift`) to safely isolate the async `Transaction.all` loop from the bridging boundary.
2. `AsyncIteratorProtocol` (Witness Table Corruption): Using a `for await` loop within an `@objc` class on iOS 15/16 triggers a known Xcode 15+ compiler bug leading to a runtime crash. We bypassed this by extracting the logic into a pure Swift struct and replacing the `for await` loop with manual `while let ... = await iterator.next()` iteration.
3. `__libcpp_verbose_abort`: Xcode 15 requires this symbol for C++ exception handling, but it is missing from the iOS 15/16 system `libc++`. We disabled verbose abort globally via `CMakeLists.txt` and provided a weak fallback implementation in `app_framework.cc` for integration tests to prevent a `dyld` launch crash.
4. `libswift_Concurrency.dylib`: The Swift compiler sometimes fails to weak-link the Concurrency backward compatibility library in Objective-C++ projects. We now natively inject `-Wl,-weak-lswift_Concurrency` into all integration test Xcode projects during `setup_integration_tests.py`.

Internal dialog comments have been cleaned up and replaced with professional explanations suitable for open-source maintainers.
Documentation in `release_build_files/readme.md` has been updated to provide clear instructions for manual C++ integrators to apply these linker/compiler flags if they experience similar crashes.

Author: AustinBenoit

CMakeLists.txt

@@ -161,6 +161,7 @@ if(DESKTOP AND APPLE)
 endif()
 
 if(APPLE)
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -D_LIBCPP_DISABLE_AVAILABILITY -D_LIBCPP_HAS_NO_VERBOSE_ABORT")
   # For iOS and macOS, disable nullability completeness warning, as it makes the
   # build output for our Objective-C++ files much too verbose.
   set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wno-nullability-completeness")
@@ -365,6 +366,7 @@ endif()
 # Include Firestore's external build early to resolve conflicts on packages.
 if(FIRESTORE_USE_EXTERNAL_CMAKE_BUILD)
   if(APPLE)
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -D_LIBCPP_DISABLE_AVAILABILITY -D_LIBCPP_HAS_NO_VERBOSE_ABORT")
     # On Apple, set GRPC_BAZEL_BUILD to fix an issue with __thread.
     # Setting this define makes gRPC use pthread's thread-local storage
     # instead of GCC's.
@@ -486,6 +488,7 @@ if(DESKTOP)
         -DUSE_LIBUV=1
       )
     elseif(APPLE)
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -D_LIBCPP_DISABLE_AVAILABILITY -D_LIBCPP_HAS_NO_VERBOSE_ABORT")
       set(websockets_additional_defines
         ${websockets_additional_defines}
         -DUSE_LIBUV=1

analytics/CMakeLists.txt

@@ -73,7 +73,7 @@ set(android_SRCS
 # Source files used by the iOS implementation.
 set(ios_SRCS
     src/analytics_ios.mm
-    src/ios/swift/StoreKit2Bridge.swift)
+    src/ios/swift/AppleTransactionVerifier.swift)
 
 # Source files used by the desktop / stub implementation.
 set(desktop_SRCS

analytics/integration_test/integration_test.xcodeproj/project.pbxproj

@@ -375,6 +375,8 @@
 		529226F71C85F68000C89379 /* Debug */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ALWAYS_SEARCH_USER_PATHS = NO;
 				CLANG_CXX_LANGUAGE_STANDARD = "gnu++0x";
 				CLANG_CXX_LIBRARY = "libc++";
@@ -418,6 +420,8 @@
 		529226F81C85F68000C89379 /* Release */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ALWAYS_SEARCH_USER_PATHS = NO;
 				CLANG_CXX_LANGUAGE_STANDARD = "gnu++0x";
 				CLANG_CXX_LIBRARY = "libc++";
@@ -455,6 +459,8 @@
 		529226FA1C85F68000C89379 /* Debug */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
 				ASSETCATALOG_COMPILER_LAUNCHIMAGE_NAME = LaunchImage;
 				CLANG_ENABLE_MODULES = YES;
@@ -487,6 +493,8 @@
 		529226FB1C85F68000C89379 /* Release */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
 				ASSETCATALOG_COMPILER_LAUNCHIMAGE_NAME = LaunchImage;
 				CLANG_ENABLE_MODULES = YES;
@@ -518,6 +526,8 @@
 		BC1D665F2668D10A005DC2DA /* Debug */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ASSETCATALOG_COMPILER_APPICON_NAME = "App Icon & Top Shelf Image";
 				ASSETCATALOG_COMPILER_GLOBAL_ACCENT_COLOR_NAME = AccentColor;
 				CLANG_ANALYZER_NONNULL = YES;
@@ -572,6 +582,8 @@
 		BC1D66602668D10A005DC2DA /* Release */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ASSETCATALOG_COMPILER_APPICON_NAME = "App Icon & Top Shelf Image";
 				ASSETCATALOG_COMPILER_GLOBAL_ACCENT_COLOR_NAME = AccentColor;
 				CLANG_ANALYZER_NONNULL = YES;

analytics/src/analytics_ios.mm

@@ -269,9 +269,14 @@ void CompleteLogAppleTransaction(const void* context, bool success) {
 
   SafeFutureHandle<void>* handle_ptr = new SafeFutureHandle<void>(future_handle);
 
-  [StoreKit2Bridge logTransaction:SafeString(transaction_id)
-                          context:handle_ptr
-                       completion:CompleteLogAppleTransaction];
+  // 2. Call Swift using a standard Objective-C block.
+  // We capture the C++ handle_ptr inside the Objective-C block. Swift never sees it.
+  [AppleTransactionVerifier verifyWithTransactionId:SafeString(transaction_id) 
+                                       completion:^(BOOL isFound) {
+      // 3. We are back in C++ land on the Main Thread. 
+      // Call your completion logic directly.
+      CompleteLogAppleTransaction(handle_ptr, isFound == YES);
+  }];
 
   return Future<void>(api, future_handle.get());
 }

analytics/src/ios/swift/AppleTransactionVerifier.swift

@@ -0,0 +1,72 @@
+// Copyright 2026 Google
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import Foundation
+import StoreKit
+import FirebaseAnalytics
+
+// Pure Swift worker to prevent compiler generation bugs with witness tables 
+// when mixing @objc and Swift Concurrency on older iOS deployment targets.
+@available(iOS 15.0, tvOS 15.0, macOS 12.0, watchOS 8.0, *)
+internal struct AppleTransactionWorker {
+    static func findAndLogTransaction(id: String) async -> Bool {
+        // Using a standard while loop instead of `for await` avoids a known 
+        // Xcode 15+ compiler bug where corrupted witness tables are generated 
+        // for AsyncSequences when targeting iOS 15/16.
+        var iterator = Transaction.all.makeAsyncIterator()
+        while let verificationResult = await iterator.next() {
+            if case .verified(let transaction) = verificationResult {
+                if String(transaction.id) == id {
+                    Analytics.logTransaction(transaction)
+                    return true
+                }
+            }
+        }
+        return false
+    }
+}
+
+@objc public class AppleTransactionVerifier: NSObject {
+    
+    // Notice: To avoid C-pointer ABI layout issues across Swift boundaries, 
+    // this interface relies purely on a standard Swift closure. The calling 
+    // C++ layer captures any necessary pointers within an Objective-C block.
+    @objc public static func verify(transactionId: String, completion: @escaping (Bool) -> Void) {
+        if #available(iOS 15.0, tvOS 15.0, macOS 12.0, watchOS 8.0, *) {
+            // Create a pure Swift String copy of the transaction ID.
+            // This ensures we do not rely on the memory of the bridged Objective-C
+            // NSString, which might be destroyed by the calling C++ thread before
+            // the asynchronous Task completes.
+            let safeId = String(transactionId)
+            
+            // Use a detached task to avoid inheriting any C++/ObjC thread context.
+            // This prevents EXC_BAD_ACCESS during `swift_task_alloc` on iOS 15/16.
+            Task.detached(priority: .userInitiated) { [safeId, completion] in
+                let isFound = await AppleTransactionWorker.findAndLogTransaction(id: safeId)
+                
+                // Return to the main thread to ensure thread safety when the C++ 
+                // layer receives the callback and manages internal state.
+                DispatchQueue.main.async {
+                    completion(isFound)
+                }
+            }
+        } else {
+            // Not on a supported OS, resolve immediately on the main thread 
+            // to avoid potential deadlocks if called while holding a C++ mutex.
+            DispatchQueue.main.async {
+                completion(false)
+            }
+        }
+    }
+}

analytics/src/ios/swift/StoreKit2Bridge.swift

@@ -210,6 +210,8 @@
 		529226F71C85F68000C89379 /* Debug */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ALWAYS_SEARCH_USER_PATHS = NO;
 				CLANG_CXX_LANGUAGE_STANDARD = "gnu++0x";
 				CLANG_CXX_LIBRARY = "libc++";
@@ -253,6 +255,8 @@
 		529226F81C85F68000C89379 /* Release */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ALWAYS_SEARCH_USER_PATHS = NO;
 				CLANG_CXX_LANGUAGE_STANDARD = "gnu++0x";
 				CLANG_CXX_LIBRARY = "libc++";
@@ -290,6 +294,8 @@
 		529226FA1C85F68000C89379 /* Debug */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
 				ASSETCATALOG_COMPILER_LAUNCHIMAGE_NAME = LaunchImage;
 				CLANG_ENABLE_MODULES = YES;
@@ -322,6 +328,8 @@
 		529226FB1C85F68000C89379 /* Release */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
 				ASSETCATALOG_COMPILER_LAUNCHIMAGE_NAME = LaunchImage;
 				CLANG_ENABLE_MODULES = YES;

app/integration_test/integration_test.xcodeproj/project.pbxproj

@@ -322,6 +322,8 @@
 		529226F71C85F68000C89379 /* Debug */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ALWAYS_SEARCH_USER_PATHS = NO;
 				CLANG_CXX_LANGUAGE_STANDARD = "gnu++0x";
 				CLANG_CXX_LIBRARY = "libc++";
@@ -365,6 +367,8 @@
 		529226F81C85F68000C89379 /* Release */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ALWAYS_SEARCH_USER_PATHS = NO;
 				CLANG_CXX_LANGUAGE_STANDARD = "gnu++0x";
 				CLANG_CXX_LIBRARY = "libc++";
@@ -402,6 +406,8 @@
 		529226FA1C85F68000C89379 /* Debug */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
 				ASSETCATALOG_COMPILER_LAUNCHIMAGE_NAME = LaunchImage;
 				CLANG_ENABLE_MODULES = YES;
@@ -435,6 +441,8 @@
 		529226FB1C85F68000C89379 /* Release */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
 				ASSETCATALOG_COMPILER_LAUNCHIMAGE_NAME = LaunchImage;
 				CLANG_ENABLE_MODULES = YES;
@@ -467,6 +475,8 @@
 		9F2ABA39267A4721001A35CE /* Debug */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ASSETCATALOG_COMPILER_APPICON_NAME = "App Icon & Top Shelf Image";
 				ASSETCATALOG_COMPILER_GLOBAL_ACCENT_COLOR_NAME = AccentColor;
 				CLANG_ANALYZER_NONNULL = YES;
@@ -521,6 +531,8 @@
 		9F2ABA3A267A4721001A35CE /* Release */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ASSETCATALOG_COMPILER_APPICON_NAME = "App Icon & Top Shelf Image";
 				ASSETCATALOG_COMPILER_GLOBAL_ACCENT_COLOR_NAME = AccentColor;
 				CLANG_ANALYZER_NONNULL = YES;

app_check/integration_test/integration_test.xcodeproj/project.pbxproj

@@ -400,6 +400,8 @@
 		529226F71C85F68000C89379 /* Debug */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ALWAYS_SEARCH_USER_PATHS = NO;
 				CLANG_CXX_LANGUAGE_STANDARD = "gnu++0x";
 				CLANG_CXX_LIBRARY = "libc++";
@@ -443,6 +445,8 @@
 		529226F81C85F68000C89379 /* Release */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ALWAYS_SEARCH_USER_PATHS = NO;
 				CLANG_CXX_LANGUAGE_STANDARD = "gnu++0x";
 				CLANG_CXX_LIBRARY = "libc++";
@@ -480,6 +484,8 @@
 		529226FA1C85F68000C89379 /* Debug */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
 				ASSETCATALOG_COMPILER_LAUNCHIMAGE_NAME = LaunchImage;
 				CLANG_ENABLE_MODULES = YES;
@@ -513,6 +519,8 @@
 		529226FB1C85F68000C89379 /* Release */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ASSETCATALOG_COMPILER_APPICON_NAME = AppIcon;
 				ASSETCATALOG_COMPILER_LAUNCHIMAGE_NAME = LaunchImage;
 				CLANG_ENABLE_MODULES = YES;
@@ -545,6 +553,8 @@
 		9F3A08FE266978C400E1D69F /* Debug */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ASSETCATALOG_COMPILER_APPICON_NAME = "App Icon & Top Shelf Image";
 				ASSETCATALOG_COMPILER_GLOBAL_ACCENT_COLOR_NAME = AccentColor;
 				CLANG_ANALYZER_NONNULL = YES;
@@ -599,6 +609,8 @@
 		9F3A08FF266978C400E1D69F /* Release */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
+				OTHER_CPLUSPLUSFLAGS = "$(inherited) -D_LIBCPP_HAS_NO_VERBOSE_ABORT -D_LIBCPP_DISABLE_AVAILABILITY";
+				OTHER_LDFLAGS = "$(inherited) -Wl,-weak-lswift_Concurrency";
 				ASSETCATALOG_COMPILER_APPICON_NAME = "App Icon & Top Shelf Image";
 				ASSETCATALOG_COMPILER_GLOBAL_ACCENT_COLOR_NAME = AccentColor;
 				CLANG_ANALYZER_NONNULL = YES;