AST: Begin accepting @cdecl on enums (but not @_cdecl)

Author: xymus

include/swift/AST/DeclAttr.def

@@ -365,7 +365,7 @@ SIMPLE_DECL_ATTR(_show_in_interface, ShowInInterface,
   62)
 
 DECL_ATTR(_cdecl, CDecl,
-  OnFunc | OnAccessor,
+  OnFunc | OnAccessor | OnEnum,
   LongAttribute | UserInaccessible | ABIStableToAdd | ABIStableToRemove | APIStableToAdd | APIStableToRemove | ForbiddenInABIAttr,
   63)
 DECL_ATTR_ALIAS(cdecl, CDecl)

lib/Sema/TypeCheckAttr.cpp

@@ -2398,6 +2398,12 @@ void AttributeChecker::visitCDeclAttr(CDeclAttr *attr) {
                attr->Name);
   }
 
+  // @_cdecl was never accepted on enums. Keep the previous diagnostic.
+  if (isa<EnumDecl>(D) && attr->Underscored) {
+    diagnose(attr->getLocation(), diag::attr_only_one_decl_kind,
+             attr, "func");
+  }
+
   if (!attr->Underscored &&
       !Ctx.LangOpts.hasFeature(Feature::CDecl)) {
     Ctx.Diags.diagnose(attr->getLocation(), diag::cdecl_feature_required);

test/attr/attr_cdecl.swift

@@ -8,7 +8,7 @@ func emptyName(x: Int) -> Int { return x }
 @_cdecl("noBody")
 func noBody(x: Int) -> Int // expected-error{{expected '{' in body of function}}
 
-@_cdecl("property") // expected-error{{may only be used on 'func' declarations}}
+@_cdecl("property") // expected-error{{'@_cdecl' attribute cannot be applied to this declaration}}
 var property: Int
 
 var computed: Int {
@@ -24,6 +24,9 @@ enum SwiftEnum { case A, B }
 @objc enum CEnum: Int { case A, B }
 #endif
 
+@_cdecl("enum") // expected-error {{@_cdecl may only be used on 'func' declarations}}
+enum UnderscoreCDeclEnum: Int { case A, B }
+
 @_cdecl("swiftStruct")
 func swiftStruct(x: SwiftStruct) {} // expected-error{{cannot be represented}} expected-note{{Swift struct}}
 
@@ -40,10 +43,10 @@ class Foo {
   @_cdecl("Foo_foo_2") // expected-error{{can only be applied to global functions}}
   static func foo(x: Int) -> Int { return x }
 
-  @_cdecl("Foo_init") // expected-error{{may only be used on 'func'}}
+  @_cdecl("Foo_init") // expected-error{{'@_cdecl' attribute cannot be applied to this declaration}}
   init() {}
 
-  @_cdecl("Foo_deinit") // expected-error{{may only be used on 'func'}}
+  @_cdecl("Foo_deinit") // expected-error{{'@_cdecl' attribute cannot be applied to this declaration}}
   deinit {}
 }
 

test/attr/attr_cdecl_official.swift

@@ -14,7 +14,7 @@ func emptyName(x: Int) -> Int { return x }
 @cdecl("noBody")
 func noBody(x: Int) -> Int // expected-error{{expected '{' in body of function}}
 
-@cdecl("property") // expected-error{{may only be used on 'func' declarations}}
+@cdecl("property") // expected-error{{'@cdecl' attribute cannot be applied to this declaration}}
 var property: Int
 
 var computed: Int {
@@ -51,10 +51,10 @@ class Foo {
   @cdecl("Foo_foo_2") // expected-error{{@cdecl can only be applied to global functions}}
   static func foo(x: Int) -> Int { return x }
 
-  @cdecl("Foo_init") // expected-error{{@cdecl may only be used on 'func'}}
+  @cdecl("Foo_init") // expected-error{{'@cdecl' attribute cannot be applied to this declaration}}
   init() {}
 
-  @cdecl("Foo_deinit") // expected-error{{@cdecl may only be used on 'func'}}
+  @cdecl("Foo_deinit") // expected-error{{'@cdecl' attribute cannot be applied to this declaration}}
   deinit {}
 }