[Concurrency] Allow 'nonisolated' to be applied to mutable storage of 'Sendable' type on a globally-isolated value type.

Author: simanerush

lib/Sema/TypeCheckAttr.cpp

@@ -6937,18 +6937,32 @@ void AttributeChecker::visitNonisolatedAttr(NonisolatedAttr *attr) {
 
   if (auto var = dyn_cast<VarDecl>(D)) {
     // stored properties have limitations as to when they can be nonisolated.
+    auto type = var->getTypeInContext();
     if (var->hasStorage()) {
-      // 'nonisolated' can not be applied to mutable stored properties unless
-      // qualified as 'unsafe'.
-      if (var->supportsMutation() && !attr->isUnsafe()) {
-        diagnoseAndRemoveAttr(attr, diag::nonisolated_mutable_storage)
-            .fixItInsertAfter(attr->getRange().End, "(unsafe)");
-        var->diagnose(diag::nonisolated_mutable_storage_note, var);
-        return;
+      {
+        // 'nonisolated' can not be applied to mutable stored properties unless
+        // qualified as 'unsafe', or is of a Sendable type on a
+        // globally-isolated value type.
+        bool canBeNonisolated = false;
+        if (dc->isTypeContext()) {
+          if (auto nominal = dc->getSelfStructDecl()) {
+            if (!var->isStatic() && type->isSendableType() &&
+                getActorIsolation(nominal).isGlobalActor()) {
+              canBeNonisolated = true;
+            }
+          }
+        }
+
+        if (var->supportsMutation() && !attr->isUnsafe() && !canBeNonisolated) {
+          diagnoseAndRemoveAttr(attr, diag::nonisolated_mutable_storage)
+              .fixItInsertAfter(attr->getRange().End, "(unsafe)");
+          var->diagnose(diag::nonisolated_mutable_storage_note, var);
+          return;
+        }
       }
 
-      // 'nonisolated' without '(unsafe)' is not allowed on non-Sendable variables.
-      auto type = var->getTypeInContext();
+      // 'nonisolated' without '(unsafe)' is not allowed on non-Sendable
+      // variables.
       if (!attr->isUnsafe() && !type->hasError()) {
         bool diagnosed = diagnoseIfAnyNonSendableTypes(
             type,

lib/Sema/TypeCheckConcurrency.cpp

@@ -515,11 +515,10 @@ static bool varIsSafeAcrossActors(const ModuleDecl *fromModule,
     // A mutable storage of a value type accessed from within the module is
     // okay.
     if (dyn_cast_or_null<StructDecl>(var->getDeclContext()->getAsDecl()) &&
-        !var->isStatic() &&
-        var->hasStorage() &&
-        var->getTypeInContext()->isSendableType() &&
-        accessWithinModule) {
-      return true;
+        !var->isStatic() && var->hasStorage() &&
+        var->getTypeInContext()->isSendableType()) {
+      if (accessWithinModule || varIsolation.isNonisolated())
+        return true;
     }
     // Otherwise, must be immutable.
     return false;

test/Concurrency/actor_isolation.swift

@@ -138,8 +138,7 @@ struct InferredFromContext {
     get { [] }
   }
 
-  nonisolated var status: Bool = true // expected-error {{'nonisolated' cannot be applied to mutable stored properties}}{{3-15=}}{{3-15=}}{{14-14=(unsafe)}}
-  // expected-note@-1{{convert 'status' to a 'let' constant or consider declaring it 'nonisolated(unsafe)' if manually managing concurrency safety}}
+  nonisolated var status: Bool = true // okay
 
   nonisolated let flag: Bool = false
 
@@ -1217,6 +1216,12 @@ func test_conforming_actor_to_global_actor_protocol() {
   // expected-error@-1 {{actor 'MyValue' cannot conform to global actor isolated protocol 'GloballyIsolatedProto'}}
 }
 
+func test_nonisolated_variable() {
+  struct S: GloballyIsolatedProto {
+    nonisolated var x: Int = 0 // okay
+  }
+}
+
 func test_invalid_reference_to_actor_member_without_a_call_note() {
   actor A {
     func partial() { }

test/Concurrency/derived_conformances_nonisolated.swift

@@ -14,7 +14,7 @@ struct X1: Equatable, Hashable, Codable {
 @MainActor
 struct X2: Equatable, Hashable, Codable {
   let x: Int
-  var y: String
+  nonisolated var y: String // okay
 }
 
 class NonSendable {

test/Concurrency/nonisolated_access.swift

@@ -0,0 +1,36 @@
+// RUN: %empty-directory(%t/src)
+// RUN: split-file %s %t/src
+
+/// Build the library A
+// RUN: %target-swift-frontend -emit-module %t/src/A.swift \
+// RUN: -disable-availability-checking \
+// RUN: -module-name A -swift-version 6 \
+// RUN: -emit-module-path %t/A.swiftmodule
+
+// Build the client
+// RUN: %target-swift-frontend -emit-module %t/src/Client.swift \
+// RUN: -disable-availability-checking \
+// RUN: -module-name Client -I %t -swift-version 6 \
+// RUN: -emit-module-path %t/Client.swiftmodule
+
+// REQUIRES: concurrency
+
+//--- A.swift
+@MainActor
+public protocol P {}
+
+public struct S: P {
+  nonisolated public var x: Int = 0
+
+  nonisolated public init() {}
+}
+
+//--- Client.swift
+import A
+
+actor A {
+  func test() {
+    var s = S()
+    s.x += 0 // okay
+  }
+}