Guard the changes behind an experimental feature flag.

Author: simanerush

include/swift/Basic/Features.def

@@ -232,6 +232,7 @@ EXPERIMENTAL_FEATURE(PreambleMacros, false)
 EXPERIMENTAL_FEATURE(TupleConformances, false)
 EXPERIMENTAL_FEATURE(FullTypedThrows, false)
 EXPERIMENTAL_FEATURE(SameElementRequirements, false)
+EXPERIMENTAL_FEATURE(GlobalActorInferenceCutoff, false)
 
 // Whether to enable @_used and @_section attributes
 EXPERIMENTAL_FEATURE(SymbolLinkageMarkers, true)

lib/AST/FeatureSet.cpp

@@ -204,6 +204,7 @@ UNINTERESTING_FEATURE(ExtractConstantsFromMembers)
 UNINTERESTING_FEATURE(FixedArrays)
 UNINTERESTING_FEATURE(GroupActorErrors)
 UNINTERESTING_FEATURE(SameElementRequirements)
+UNINTERESTING_FEATURE(GlobalActorInferenceCutoff)
 
 static bool usesFeatureSendingArgsAndResults(Decl *decl) {
   auto isFunctionTypeWithSending = [](Type type) {

lib/Sema/TypeCheckAttr.cpp

@@ -7127,6 +7127,15 @@ void AttributeChecker::visitNonisolatedAttr(NonisolatedAttr *attr) {
   // 'nonisolated' can be applied to global and static/class variables
   // that do not have storage.
   auto dc = D->getDeclContext();
+  auto &ctx = D->getASTContext();
+
+  if (!ctx.LangOpts.hasFeature(Feature::GlobalActorInferenceCutoff)) {
+    if (isa<ProtocolDecl>(D) || isa<ExtensionDecl>(D) || isa<ClassDecl>(D) ||
+        isa<StructDecl>(D) || isa<EnumDecl>(D)) {
+      diagnoseAndRemoveAttr(attr, diag::invalid_decl_modifier, attr);
+      return;
+    }
+  }
 
   // nonisolated(unsafe) is unsafe, but only under strict concurrency.
   if (attr->isUnsafe() &&
@@ -7149,12 +7158,14 @@ void AttributeChecker::visitNonisolatedAttr(NonisolatedAttr *attr) {
           }
         }
 
-        // Additionally, a stored property of a non-'Sendable' type can be
-        // explicitly marked 'nonisolated'.
-        if (auto parentDecl = dc->getDeclaredTypeInContext())
-          if (!parentDecl->isSendableType()) {
-            canBeNonisolated = true;
-          }
+        if (ctx.LangOpts.hasFeature(Feature::GlobalActorInferenceCutoff)) {
+          // Additionally, a stored property of a non-'Sendable' type can be
+          // explicitly marked 'nonisolated'.
+          if (auto parentDecl = dc->getDeclaredTypeInContext())
+            if (!parentDecl->isSendableType()) {
+              canBeNonisolated = true;
+            }
+        }
 
         // Otherwise, this stored property has to be qualified as 'unsafe'.
         if (var->supportsMutation() && !attr->isUnsafe() && !canBeNonisolated) {
@@ -7164,14 +7175,16 @@ void AttributeChecker::visitNonisolatedAttr(NonisolatedAttr *attr) {
           return;
         }
 
-        // 'nonisolated' without '(unsafe)' is not allowed on non-Sendable
-        // variables, unless they are a member of a non-'Sendable' type.
-        if (!attr->isUnsafe() && !type->hasError() && !canBeNonisolated) {
-          bool diagnosed = diagnoseIfAnyNonSendableTypes(
-              type, SendableCheckContext(dc), Type(), SourceLoc(),
-              attr->getLocation(), diag::nonisolated_non_sendable);
-          if (diagnosed)
-            return;
+        if (ctx.LangOpts.hasFeature(Feature::GlobalActorInferenceCutoff)) {
+          // 'nonisolated' without '(unsafe)' is not allowed on non-Sendable
+          // variables, unless they are a member of a non-'Sendable' type.
+          if (!attr->isUnsafe() && !type->hasError() && !canBeNonisolated) {
+            bool diagnosed = diagnoseIfAnyNonSendableTypes(
+                type, SendableCheckContext(dc), Type(), SourceLoc(),
+                attr->getLocation(), diag::nonisolated_non_sendable);
+            if (diagnosed)
+              return;
+          }
         }
       }
 

test/Concurrency/nonisolated_rules.swift

@@ -1,5 +1,4 @@
-// RUN: %target-swift-frontend -disable-availability-checking -swift-version 6 -parse-as-library %s -emit-sil -o /dev/null -verify
-// RUN: %target-swift-frontend -disable-availability-checking -swift-version 6 -parse-as-library %s -emit-sil -o /dev/null -verify -strict-concurrency=complete
+// RUN: %target-swift-frontend -disable-availability-checking -swift-version 6 -enable-experimental-feature GlobalActorInferenceCutoff -parse-as-library %s -emit-sil -o /dev/null -verify -strict-concurrency=complete
 
 // REQUIRES: concurrency
 // REQUIRES: asserts