[Concurrency] Allow globally isolated closures to capture non-Sendable values.

Author: simanerush

lib/Sema/TypeCheckConcurrency.cpp

@@ -4181,15 +4181,21 @@ bool ActorIsolationChecker::mayExecuteConcurrentlyWith(
     if (useIsolation == defIsolation)
       return false;
 
+    auto &ctx = useContext->getASTContext();
+    bool regionIsolationEnabled =
+        ctx.LangOpts.hasFeature(Feature::RegionBasedIsolation);
+    
+    // Globally-isolated closures may never be executed concurrently.
+    if (ctx.LangOpts.hasFeature(Feature::GlobalActorIsolatedTypesUsability) &&
+        regionIsolationEnabled && useIsolation.isGlobalActor())
+      return false;
+
     // If the local function is not Sendable, its isolation differs
     // from that of the context, and both contexts are actor isolated,
     // then capturing non-Sendable values allows the closure to stash
     // those values into actor isolated state. The original context
     // may also stash those values into isolated state, enabling concurrent
     // access later on.
-    auto &ctx = useContext->getASTContext();
-    bool regionIsolationEnabled =
-        ctx.LangOpts.hasFeature(Feature::RegionBasedIsolation);
     isolatedStateMayEscape =
         (!regionIsolationEnabled &&
         useIsolation.isActorIsolated() && defIsolation.isActorIsolated());

test/Concurrency/global_actor_sendable_fn_type_inference.swift

@@ -10,3 +10,12 @@ func inferSendableFunctionType() {
     await closure() // okay
   }
 }
+
+class NonSendable {}
+
+func allowNonSendableCaptures() {
+  let nonSendable = NonSendable()
+  let _: @MainActor () -> Void = {
+    let _ = nonSendable // okay
+  }
+}