[ObjC] Stop hard-coding the list of keywords that are allowed in selectors (#138952)

The design intent is that ObjC selector pieces can be arbitrary
keywords, including basic C keywords like `if`, and the grammar permits
this and makes it unambiguous.

Allow any token that has an identifier (except `__attribute__`) to be
part of a selector.

rdar://150383689

Author: ahatanak

clang/lib/Parse/ParseObjc.cpp

@@ -1067,8 +1067,6 @@ Decl *Parser::ParseObjCMethodPrototype(tok::ObjCKeywordKind MethodImplKind,
 IdentifierInfo *Parser::ParseObjCSelectorPiece(SourceLocation &SelectorLoc) {
 
   switch (Tok.getKind()) {
-  default:
-    return nullptr;
   case tok::colon:
     // Empty selector piece uses the location of the ':'.
     SelectorLoc = Tok.getLocation();
@@ -1094,77 +1092,13 @@ IdentifierInfo *Parser::ParseObjCSelectorPiece(SourceLocation &SelectorLoc) {
     return nullptr;
   }
 
-  case tok::identifier:
-  case tok::kw_asm:
-  case tok::kw_auto:
-  case tok::kw_bool:
-  case tok::kw_break:
-  case tok::kw_case:
-  case tok::kw_catch:
-  case tok::kw_char:
-  case tok::kw_class:
-  case tok::kw_const:
-  case tok::kw_const_cast:
-  case tok::kw_continue:
-  case tok::kw_default:
-  case tok::kw_delete:
-  case tok::kw_do:
-  case tok::kw_double:
-  case tok::kw_dynamic_cast:
-  case tok::kw_else:
-  case tok::kw_enum:
-  case tok::kw_explicit:
-  case tok::kw_export:
-  case tok::kw_extern:
-  case tok::kw_false:
-  case tok::kw_float:
-  case tok::kw_for:
-  case tok::kw_friend:
-  case tok::kw_goto:
-  case tok::kw_if:
-  case tok::kw_inline:
-  case tok::kw_int:
-  case tok::kw_long:
-  case tok::kw_mutable:
-  case tok::kw_namespace:
-  case tok::kw_new:
-  case tok::kw_operator:
-  case tok::kw_private:
-  case tok::kw_protected:
-  case tok::kw_public:
-  case tok::kw_register:
-  case tok::kw_reinterpret_cast:
-  case tok::kw_restrict:
-  case tok::kw_return:
-  case tok::kw_short:
-  case tok::kw_signed:
-  case tok::kw_sizeof:
-  case tok::kw_static:
-  case tok::kw_static_cast:
-  case tok::kw_struct:
-  case tok::kw_switch:
-  case tok::kw_template:
-  case tok::kw_this:
-  case tok::kw_throw:
-  case tok::kw_true:
-  case tok::kw_try:
-  case tok::kw_typedef:
-  case tok::kw_typeid:
-  case tok::kw_typename:
-  case tok::kw_typeof:
-  case tok::kw_union:
-  case tok::kw_unsigned:
-  case tok::kw_using:
-  case tok::kw_virtual:
-  case tok::kw_void:
-  case tok::kw_volatile:
-  case tok::kw_wchar_t:
-  case tok::kw_while:
-  case tok::kw__Bool:
-  case tok::kw__Complex:
-  case tok::kw___alignof:
-  case tok::kw___auto_type:
+  case tok::kw___attribute:
+    return nullptr;
+
+  default:
     IdentifierInfo *II = Tok.getIdentifierInfo();
+    if (!II)
+      return nullptr;
     SelectorLoc = ConsumeToken();
     return II;
   }

clang/test/SemaObjCXX/cxxoperator-selector.mm

@@ -19,5 +19,10 @@ - (id) and{return 0; };
 - (id) xor{return 0; };
 - (id) or{return 0; };
 
+- (void)decltype {}
+- (void)constexpr {}
+- (void)noexcept {}
+- (void)nullptr {}
+
 - (void)dataSetForValuesBetween:(NSDate *)startDate and:(NSDate *)endDate { return; }
 @end