Enforce the C++11 anonymous enum bitfields check even for

Objective-C++11 and under MS extensions.

This matches the MSVC behavior, and means that Objective-C behaves as a
set of extensions to the base language, rather than replacing the base
language rule with a different one.

clang/lib/Parse/ParseDecl.cpp

@@ -4543,8 +4543,7 @@ void Parser::ParseEnumSpecifier(SourceLocation StartLoc, DeclSpec &DS,
     if (CanBeBitfield && !isEnumBase(CanBeOpaqueEnumDeclaration)) {
       // Outside C++11, do not interpret the tokens as an enum-base if they do
       // not make sense as one. In C++11, it's an error if this happens.
-      if (getLangOpts().CPlusPlus11 && !getLangOpts().ObjC &&
-          !getLangOpts().MicrosoftExt)
+      if (getLangOpts().CPlusPlus11)
         Diag(Tok.getLocation(), diag::err_anonymous_enum_bitfield);
     } else if (CanHaveEnumBase || !ColonIsSacred) {
       SourceLocation ColonLoc = ConsumeToken();

clang/test/Parser/MicrosoftExtensions.cpp

@@ -455,4 +455,17 @@ namespace enum_class {
   auto f4() -> enum class E4 { return {}; }
   auto f5() -> enum E5 : int { return {}; } // FIXME: MSVC rejects this and crashes if the body is {}.
   auto f6() -> enum E6 { return {}; } // expected-warning {{Microsoft extension}}
+
+  // MSVC does not perform disambiguation for a colon that could introduce an
+  // enum-base or a bit-field.
+  enum E {};
+  struct S {
+    enum E : int(1); // expected-error {{anonymous bit-field}}
+    enum E : int : 1; // OK, bit-field
+    enum F : int a = {}; // OK, default member initializer
+    // MSVC produces a "C4353 constant 0 as function expression" for this,
+    // considering the final {} to be part of the bit-width. We follow P0683R1
+    // and treat it as a default member initializer.
+    enum E : int : int{}{}; // expected-error {{anonymous bit-field cannot have a default member initializer}} expected-warning {{C++20 extension}}
+  };
 }

clang/test/Parser/objcxx-enum.mm

@@ -1,10 +1,14 @@
 // RUN: %clang_cc1 -verify -std=c++98 %s
+// RUN: %clang_cc1 -verify=cxx11 -std=c++11 %s
+
+#if __cplusplus < 201103L
 // expected-no-diagnostics
+#endif
 
 // Objective-C allows C++11 enumerations in C++98 mode. We disambiguate in
 // order to make this a backwards-compatible extension.
 struct A {
   enum E : int{a}; // OK, enum definition
-  enum E : int(a); // OK, bit-field declaration
+  enum E : int(a); // OK, bit-field declaration cxx11-error{{anonymous bit-field}}
 };
 _Static_assert(A::a == 0, "");

clang/test/SemaCXX/MicrosoftExtensions.cpp

@@ -154,6 +154,9 @@ struct X0 {
 #endif
 
   enum E1 : seventeen;
+#if __cplusplus >= 201103L
+  // expected-error@-2 {{bit-field}}
+#endif
 };
 
 #if __cplusplus <= 199711L