Add a feature flag for DisableActorInferenceFromPropertyWrapperUsage.

This will be enabled by default in Swift 6, but can now also be enabled by passing `-enable-upcoming-feature DisableActorInferenceFromPropertyWrapperUsage` to the compiler.

(cherry picked from commit f876f26)

Author: bjhomer

include/swift/Basic/Features.def

@@ -113,6 +113,7 @@ UPCOMING_FEATURE(ForwardTrailingClosures, 286, 6)
 UPCOMING_FEATURE(BareSlashRegexLiterals, 354, 6)
 UPCOMING_FEATURE(ExistentialAny, 335, 6)
 UPCOMING_FEATURE(ImportObjcForwardDeclarations, 384, 6)
+UPCOMING_FEATURE(DisableActorInferenceFromPropertyWrapperUsage, 0, 6)
 
 EXPERIMENTAL_FEATURE(StaticAssert, false)
 EXPERIMENTAL_FEATURE(NamedOpaqueTypes, false)

lib/AST/ASTPrinter.cpp

@@ -3346,6 +3346,10 @@ static bool usesFeatureFreestandingExpressionMacros(Decl *decl) {
   return macro->getMacroRoles().contains(MacroRole::Expression);
 }
 
+static bool usesFeatureDisableActorInferenceFromPropertyWrapperUsage(Decl *decl) {
+  return false;
+}
+
 static void
 suppressingFeatureNoAsyncAvailability(PrintOptions &options,
                                       llvm::function_ref<void()> action) {

lib/Sema/TypeCheckConcurrency.cpp

@@ -3624,7 +3624,7 @@ static Optional<ActorIsolation> getIsolationFromWrappers(
     return None;
 
   ASTContext &ctx = nominal->getASTContext();
-  if (ctx.isSwiftVersionAtLeast(6)) {
+  if (ctx.LangOpts.hasFeature(Feature::DisableActorInferenceFromPropertyWrapperUsage)) {
     // In Swift 6, we no longer infer isolation of a nominal type
     // based on the property wrappers used in its stored properties
     return None;