[concurrency] When calling an imported async objc function using continuations, use merge_isolation_region to tie the block storage and the resume buffer into one region.

This ensures that if the block has an @out return value that the return value is
considered to be affected by the actual call of the block. Before b/c we
smuggled the value through a Sendable continuation, we would lose the connection
in between the block and that result.

rdar://131422332

Author: gottesmm

lib/SILGen/ResultPlan.cpp

@@ -806,6 +806,12 @@ class ForeignAsyncInitializationPlan final : public ResultPlan {
     std::tie(blockStorage, blockStorageTy, continuationTy) =
         emitBlockStorage(SGF, loc, throws);
 
+    // Add a merge_isolation_region from the continuation result buffer
+    // (resumeBuf) onto the block storage so it is in the same region as the
+    // block storage despite the intervening Sendable continuation wrapping that
+    // disguises this fact from the region isolation checker.
+    SGF.B.createMergeIsolationRegion(loc, {blockStorage, resumeBuf});
+
     // Get the block invocation function for the given completion block type.
     auto completionHandlerIndex = calleeTypeInfo.foreign.async
       ->completionHandlerParamIndex();

test/Concurrency/Inputs/transfernonsendable_objc.h

@@ -9,3 +9,15 @@
 @protocol MySession <NSObject>
 - (void)endSession;
 @end
+
+typedef NSString *MyStringEnum NS_EXTENSIBLE_STRING_ENUM;
+
+@interface MyAssetTrack : NSObject
+@end
+
+@interface MyAsset : NSObject
+
+- (void)loadTracksWithStringEnum:(MyStringEnum)stringEnum completionHandler:(void (^)(NSArray<MyAssetTrack *> * _Nullable, NSError * _Nullable)) completionHandler;
+
+@end
+

test/Concurrency/transfernonsendable_objc.swift

@@ -25,3 +25,9 @@ actor MyActor {
     defer { session?.end() }
   }
 }
+
+extension MyAsset {
+  func continuationResultTiedToContinuation(withStringEnum stringEnum: MyStringEnum) async throws -> sending [MyAssetTrack] {
+    try await loadTracks(withStringEnum: stringEnum)
+  }
+}