[Concurrency] Only infer extension/nominal actor for instance members.

Fixes rdar://72966018.

Author: DougGregor

lib/Sema/TypeCheckConcurrency.cpp

@@ -1886,20 +1886,23 @@ ActorIsolation ActorIsolationRequest::evaluate(
     }
   }
 
-  // If the declaration is in an extension that has one of the isolation
-  // attributes, use that.
-  if (auto ext = dyn_cast<ExtensionDecl>(value->getDeclContext())) {
-    if (auto isolationFromAttr = getIsolationFromAttributes(ext)) {
-      return inferredIsolation(*isolationFromAttr);
+  // Instance members can infer isolation from their context.
+  if (value->isInstanceMember()) {
+    // If the declaration is in an extension that has one of the isolation
+    // attributes, use that.
+    if (auto ext = dyn_cast<ExtensionDecl>(value->getDeclContext())) {
+      if (auto isolationFromAttr = getIsolationFromAttributes(ext)) {
+        return inferredIsolation(*isolationFromAttr);
+      }
     }
-  }
 
-  // If the declaration is in a nominal type (or extension thereof) that
-  // has isolation, use that.
-  if (auto selfTypeDecl = value->getDeclContext()->getSelfNominalTypeDecl()) {
-    auto selfTypeIsolation = getActorIsolation(selfTypeDecl);
-    if (!selfTypeIsolation.isUnspecified()) {
-      return inferredIsolation(selfTypeIsolation);
+    // If the declaration is in a nominal type (or extension thereof) that
+    // has isolation, use that.
+    if (auto selfTypeDecl = value->getDeclContext()->getSelfNominalTypeDecl()) {
+      auto selfTypeIsolation = getActorIsolation(selfTypeDecl);
+      if (!selfTypeIsolation.isUnspecified()) {
+        return inferredIsolation(selfTypeIsolation);
+      }
     }
   }
 

test/Concurrency/actor_isolation.swift

@@ -406,4 +406,20 @@ actor class LazyActor {
     @actorIndependent lazy var l43: Int = { self.l }()
     @actorIndependent lazy var l44: Int = self.l
     @actorIndependent lazy var l45: Int = { [unowned self] in self.l }()
-}
+}
+
+// Infer global actors from context only for instance members.
+@MainActor
+class SomeClassInActor {
+  enum ID: String { case best }
+
+  func inActor() { } // expected-note{{calls to instance method 'inActor()' from outside of its actor context are implicitly asynchronous}}
+}
+
+extension SomeClassInActor.ID {
+  func f(_ object: SomeClassInActor) { // expected-note{{add '@MainActor' to make instance method 'f' part of global actor 'MainActor'}}
+    // expected-note@-1{{add 'async' to function 'f' to make it asynchronous}}
+    // expected-note@-2{{add '@asyncHandler' to function 'f' to create an implicit asynchronous context}}
+    object.inActor() // expected-error{{'async' in a function that does not support concurrency}}
+  }
+}