[Frontend] Mark 'Type Wrappers' as experimental feature that has to be enabled

Author: xedin

include/swift/AST/DiagnosticsSema.def

@@ -6480,6 +6480,9 @@ ERROR(move_expression_not_passed_lvalue,none,
 // MARK: Type Wrappers
 //------------------------------------------------------------------------------
 
+ERROR(type_wrappers_are_experimental,none,
+      "type wrappers are an experimental feature", ())
+
 ERROR(type_wrapper_attribute_not_allowed_here,none,
       "type wrapper attribute %0 can only be applied to a class, struct",
       (Identifier))

include/swift/Basic/Features.def

@@ -122,6 +122,11 @@ EXPERIMENTAL_FEATURE(SendableCompletionHandlers)
 /// Enables opaque type erasure without also enabling implict dynamic
 EXPERIMENTAL_FEATURE(OpaqueTypeErasure)
 
+/// Whether to enable experimental @typeWrapper feature which allows to
+/// declare a type that controls access to all stored properties of the
+/// wrapped type.
+EXPERIMENTAL_FEATURE(TypeWrappers)
+
 #undef EXPERIMENTAL_FEATURE
 #undef UPCOMING_FEATURE
 #undef SUPPRESSIBLE_LANGUAGE_FEATURE

lib/AST/ASTPrinter.cpp

@@ -2935,6 +2935,10 @@ static bool usesFeatureSpecializeAttributeWithAvailability(Decl *decl) {
   return false;
 }
 
+static bool usesFeatureTypeWrappers(Decl *decl) {
+  return decl->getAttrs().hasAttribute<TypeWrapperAttr>();
+}
+
 static void suppressingFeatureSpecializeAttributeWithAvailability(
                                         PrintOptions &options,
                                         llvm::function_ref<void()> action) {

lib/Sema/TypeCheckAttr.cpp

@@ -3587,6 +3587,12 @@ void AttributeChecker::visitPropertyWrapperAttr(PropertyWrapperAttr *attr) {
 }
 
 void AttributeChecker::visitTypeWrapperAttr(TypeWrapperAttr *attr) {
+  if (!Ctx.LangOpts.hasFeature(Feature::TypeWrappers)) {
+    diagnose(attr->getLocation(), diag::type_wrappers_are_experimental);
+    attr->setInvalid();
+    return;
+  }
+
   auto nominal = dyn_cast<NominalTypeDecl>(D);
   if (!nominal)
     return;

test/Interpreter/type_wrappers.swift

@@ -1,5 +1,5 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-build-swift -parse-as-library -emit-library -emit-module-path %t/type_wrapper_defs.swiftmodule -module-name type_wrapper_defs %S/Inputs/type_wrapper_defs.swift -o %t/%target-library-name(type_wrapper_defs)
+// RUN: %target-build-swift -enable-experimental-feature TypeWrappers -parse-as-library -emit-library -emit-module-path %t/type_wrapper_defs.swiftmodule -module-name type_wrapper_defs %S/Inputs/type_wrapper_defs.swift -o %t/%target-library-name(type_wrapper_defs)
 // RUN: %target-build-swift -ltype_wrapper_defs -module-name main -I %t -L %t %s -o %t/a.out
 // RUN: %target-run %t/a.out | %FileCheck %s
 

test/type/type_wrapper.swift

@@ -1,4 +1,4 @@
-// RUN: %target-typecheck-verify-swift
+// RUN: %target-typecheck-verify-swift -enable-experimental-feature TypeWrappers
 
 @typeWrapper
 struct ConcreteTypeWrapper { // expected-error {{type wrapper has to declare a single generic parameter for underlying storage type}}