Merge pull request #40092 from DougGregor/closure-isolated-param-isolation

Isolate closures to their 'isolated' parameters.

Author: DougGregor

lib/Sema/TypeCheckConcurrency.cpp

@@ -2611,6 +2611,13 @@ namespace {
           return ClosureActorIsolation::forGlobalActor(globalActorType);
       }
 
+      // If a closure has an isolated parameter, it is isolated to that
+      // parameter.
+      for (auto param : *closure->getParameters()) {
+        if (param->isIsolated())
+          return ClosureActorIsolation::forActorInstance(param);
+      }
+
       // Sendable closures are actor-independent unless the closure has
       // specifically opted into inheriting actor isolation.
       if (isSendableClosure(closure, /*forActorIsolation=*/true))

test/Concurrency/isolated_parameters.swift

@@ -144,3 +144,19 @@ func testExistentialIsolated(a: isolated P2, b: P2) async {
   b.m() // expected-error{{expression is 'async' but is not marked with 'await'}}
   // expected-note@-1{{calls to instance method 'm()' from outside of its actor context are implicitly asynchronous}}
 }
+
+// "isolated" parameters of closures make the closure itself isolated.
+extension TestActor {
+  func isolatedMethod() { }
+}
+
+@available(SwiftStdlib 5.1, *)
+func isolatedClosures() {
+  let _: (isolated TestActor) -> Void = { (ta: isolated TestActor) in
+    ta.isolatedMethod() // okay, isolated to ta
+
+    _ = {
+      ta.isolatedMethod() // okay, isolated to ta
+    }
+  }
+}