[Sema]: Fix data race safety hole with mutable statics within actors

Update the concurrency typechecking logic to remove a check that allowed
mutable static variable declarations nested within an Actor type to be
ignored when diagnosing mutable non-Sendable state.

Author: jamieQ

lib/Sema/TypeCheckConcurrency.cpp

@@ -6202,9 +6202,7 @@ void swift::checkGlobalIsolation(VarDecl *var) {
       var->getASTContext().LangOpts.hasFeature(Feature::GlobalConcurrency) &&
       !isolation.isGlobalActor() &&
       (isolation != ActorIsolation::NonisolatedUnsafe)) {
-    auto *classDecl = var->getDeclContext()->getSelfClassDecl();
-    const bool isActorType = classDecl && classDecl->isAnyActor();
-    if (var->isGlobalStorage() && !isActorType) {
+    if (var->isGlobalStorage()) {
       auto *diagVar = var;
       if (auto *originalVar = var->getOriginalWrappedProperty()) {
         diagVar = originalVar;

test/Concurrency/global_variables.swift

@@ -8,7 +8,7 @@
 
 @globalActor
 actor TestGlobalActor {
-  static var shared = TestGlobalActor()
+  static let shared = TestGlobalActor()
 }
 
 @TestGlobalActor
@@ -72,6 +72,38 @@ struct TestStatics {
 public actor TestPublicActor {
   nonisolated(unsafe) let immutableNonisolatedUnsafeSendable = TestSendable()
   // expected-warning@-1 {{'(unsafe)' is unnecessary for a constant public actor property with 'Sendable' type 'TestSendable', consider removing it}} {{14-22=}}
+
+  // https://github.com/swiftlang/swift/issues/78435
+  static var actorStatic = 0
+  // expected-error@-1 {{static property 'actorStatic' is not concurrency-safe because it is nonisolated global shared mutable state}}
+  // expected-note@-2{{convert 'actorStatic' to a 'let' constant to make 'Sendable' shared state immutable}}{{10-13=let}}
+  // expected-note@-3{{disable concurrency-safety checks if accesses are protected by an external synchronization mechanism}}{{3-3=nonisolated(unsafe) }}
+  // expected-note@-4{{add '@MainActor' to make static property 'actorStatic' part of global actor 'MainActor'}}{{3-3=@MainActor }}
+}
+
+enum EnumSpace {
+  static let enumStaticLet = TestSendable()
+
+  static var enumStatic = 0
+  // expected-error@-1 {{static property 'enumStatic' is not concurrency-safe because it is nonisolated global shared mutable state}}
+  // expected-note@-2{{convert 'enumStatic' to a 'let' constant to make 'Sendable' shared state immutable}}{{10-13=let}}
+  // expected-note@-3{{disable concurrency-safety checks if accesses are protected by an external synchronization mechanism}}{{3-3=nonisolated(unsafe) }}
+  // expected-note@-4{{add '@MainActor' to make static property 'enumStatic' part of global actor 'MainActor'}}{{3-3=@MainActor }}
+}
+
+@TestGlobalActor
+enum IsolatedEnumSpace {
+  static let inferredGlobalActorStaticLet = TestSendable()
+
+  static var inferredGlobalActorStatic = 0
+}
+
+public actor GlobalActorComputed: GlobalActor {
+  static let storage = GlobalActorComputed()
+
+  public static var shared: GlobalActorComputed {
+    Self.storage
+  }
 }
 
 @TestGlobalActor