[Actor isolation] Initializers don't infer global actor isolation.

Initializers within a global-actor-isolated type are not inferred to
be global-actor-isolated themselves, because that isn't generally what
one wants: usually, you want to be able to create an instance of
the type by calling the initializer from somewhere.

Within such initializers, allow access to the stored properties on
"self" regardless.

Fixes rdar://75450300.

Author: DougGregor

lib/Sema/TypeCheckConcurrency.cpp

@@ -2186,6 +2186,13 @@ namespace {
         LLVM_FALLTHROUGH;
 
       case ActorIsolationRestriction::GlobalActor:
+        // If we are within an initializer and are referencing a stored
+        // property on "self", we are not crossing actors.
+        if (isa<ConstructorDecl>(getDeclContext()) &&
+            isa<VarDecl>(member) && cast<VarDecl>(member)->hasStorage() &&
+            getReferencedSelf(base))
+          return false;
+
         return checkGlobalActorReference(
             memberRef, memberLoc, isolation.getGlobalActor(),
             isolation.isCrossActor, context);
@@ -2688,8 +2695,8 @@ ActorIsolation ActorIsolationRequest::evaluate(
     }
   }
 
-  // Instance members and initializers can infer isolation from their context.
-  if (value->isInstanceMember() || isa<ConstructorDecl>(value)) {
+  // Instance members 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())) {

test/Concurrency/actor_isolation.swift

@@ -651,10 +651,10 @@ class SomeClassWithInits {
     self.mutableState = 42
     self.otherMutableState = 17
 
-    self.isolated()
+    self.isolated() // expected-error{{'isolated()' isolated to global actor 'MainActor' can not be referenced from this synchronous context}}
   }
 
-  func isolated() { }
+  func isolated() { } // expected-note{{calls to instance method 'isolated()' from outside of its actor context are implicitly asynchronous}}
 
   func hasDetached() {
     Task.runDetached {
@@ -668,6 +668,10 @@ class SomeClassWithInits {
   }
 }
 
+func outsideSomeClassWithInits() {
+  _ = SomeClassWithInits() // okay, initializer is not isolated
+}
+
 // ----------------------------------------------------------------------
 // Actor protocols.
 // ----------------------------------------------------------------------