[Concurrency] Centralize rejection of concurrency-only attributes.

Reject concurrency-only attributes in the parser if the experimental
concurrency mode is not enabled.

Author: DougGregor

include/swift/AST/Attr.def

@@ -562,7 +562,7 @@ SIMPLE_DECL_ATTR(noDerivative, NoDerivative,
   100)
 
 SIMPLE_DECL_ATTR(asyncHandler, AsyncHandler,
-  OnFunc | UserInaccessible |
+  OnFunc | ConcurrencyOnly |
   ABIStableToAdd | ABIStableToRemove | APIStableToAdd | APIStableToRemove,
   101)
 

include/swift/AST/DiagnosticsParse.def

@@ -1748,6 +1748,11 @@ ERROR(pound_available_package_description_not_allowed, none,
 ERROR(availability_query_repeated_platform, none,
       "version for '%0' already specified", (StringRef))
 
+ERROR(attr_requires_concurrency,none,
+      "'%0' %select{attribute|modifier}1 is only valid when experimental "
+      "concurrency is enabled",
+      (StringRef, bool))
+
 //------------------------------------------------------------------------------
 // MARK: syntax parsing diagnostics
 //------------------------------------------------------------------------------

include/swift/AST/DiagnosticsSema.def

@@ -4107,9 +4107,6 @@ NOTE(protocol_witness_async_conflict,none,
 ERROR(async_autoclosure_nonasync_function,none,
       "'async' autoclosure parameter in a non-'async' function", ())
 
-ERROR(asynchandler_attr_requires_concurrency,none,
-      "'@asyncHandler' is only valid when experimental concurrency is enabled",
-      ())
 ERROR(asynchandler_non_func,none,
       "'@asyncHandler' can only be applied to functions",
       ())
@@ -4142,8 +4139,6 @@ ERROR(satisfy_async_objc,none,
 ERROR(async_objc_dynamic_self,none,
       "asynchronous method returning 'Self' cannot be '@objc'", ())
 
-ERROR(actor_without_concurrency,none,
-      "'actor' classes require experimental concurrency support", ())
 ERROR(actor_with_nonactor_superclass,none,
       "actor class cannot inherit from non-actor class %0", (DeclName))
 

lib/Parse/ParseDecl.cpp

@@ -1394,6 +1394,15 @@ bool Parser::parseNewDeclAttribute(DeclAttributes &Attributes, SourceLoc AtLoc,
     DiscardAttribute = true;
   }
 
+  // If this attribute is only permitted when concurrency is enabled, reject it.
+  if (DeclAttribute::isConcurrencyOnly(DK) &&
+      !shouldParseExperimentalConcurrency()) {
+    diagnose(
+        Loc, diag::attr_requires_concurrency, AttrName,
+        DeclAttribute::isDeclModifier(DK));
+    DiscardAttribute = true;
+  }
+
   if (Context.LangOpts.Target.isOSBinFormatCOFF()) {
     if (DK == DAK_WeakLinked) {
       diagnose(Loc, diag::attr_unsupported_on_target, AttrName,

lib/Sema/TypeCheckAttr.cpp

@@ -259,11 +259,6 @@ class AttributeChecker : public AttributeVisitor<AttributeChecker> {
   void visitTransposeAttr(TransposeAttr *attr);
 
   void visitAsyncHandlerAttr(AsyncHandlerAttr *attr) {
-    if (!Ctx.LangOpts.EnableExperimentalConcurrency) {
-      diagnoseAndRemoveAttr(attr, diag::asynchandler_attr_requires_concurrency);
-      return;
-    }
-
     auto func = dyn_cast<FuncDecl>(D);
     if (!func) {
       diagnoseAndRemoveAttr(attr, diag::asynchandler_non_func);

lib/Sema/TypeCheckConcurrency.cpp

@@ -161,14 +161,6 @@ bool IsActorRequest::evaluate(
     Evaluator &evaluator, ClassDecl *classDecl) const {
   // If concurrency is not enabled, we don't have actors.
   auto actorAttr = classDecl->getAttrs().getAttribute<ActorAttr>();
-  if (!classDecl->getASTContext().LangOpts.EnableExperimentalConcurrency) {
-    if (actorAttr) {
-      classDecl->diagnose(diag::actor_without_concurrency)
-          .highlight(actorAttr->getRange());
-    }
-
-    return false;
-  }
 
   // If there is a superclass, we can infer actor-ness from it.
   if (auto superclassDecl = classDecl->getSuperclassDecl()) {

test/attr/asynchandler_noconcurrency.swift

@@ -1,4 +1,4 @@
 // RUN: %target-swift-frontend -typecheck -verify %s
 
 @asyncHandler func asyncHandler1() { }
-// expected-error@-1{{'@asyncHandler' is only valid when experimental concurrency is enabled}}
+// expected-error@-1{{'asyncHandler' attribute is only valid when experimental concurrency is enabled}}

test/decl/class/actor/noconcurrency.swift

@@ -1,4 +1,4 @@
 // RUN: %target-typecheck-verify-swift
 
-actor class C { } // expected-error{{'actor' classes require experimental concurrency support}}
+actor class C { } // expected-error{{'actor' attribute is only valid when experimental concurrency is enabled}}