[ms] Give -Wmicrosoft-enum-forward-reference a chance to fire in clang-cl, PR32736

[thakis]

Summary

clang-cl sets MicrosoftCompat. In that mode, we always give enums a fixed underlying type, and for enums with fixed underlying type we never enter the block that tries to emit ext_ms_forward_ref_enum. Fix this by requiring an explicit underlying type when we're skipping this diagnostic.

We had a test for this warning, but it only ran in C++98 mode. clang-cl always enables -std=c++14, so MicrosoftCompatibiliy-cxx98.cpp is a fairly useless test. Fold it into MicrosoftCompatibility.cpp -- that way, the test checks if -Wmicrosoft-enum-forward-reference can fire in clang-cl builds.

[hans]

lgtm

[thakis]

r301032, thanks.

lib/Sema/SemaDecl.cpp

New = EnumDecl::Create(Context, SearchDC, KWLoc, Loc, Name,
                            ScopedEnumUsesClassTag, !EnumUnderlying.isNull());
 
     if (isStdAlignValT && (!StdAlignValT || getStdAlignValT()->isImplicit()))
       StdAlignValT = cast<EnumDecl>(New);
 
     // If this is an undefined enum, warn.
     if (TUK != TUK_Definition && !Invalid) {
       TagDecl *Def;
-      if ((getLangOpts().CPlusPlus11 || getLangOpts().ObjC2) &&
+      if (!EnumUnderlyingIsImplicit &&
+          (getLangOpts().CPlusPlus11 || getLangOpts().ObjC2) &&
           cast<EnumDecl>(New)->isFixed()) {
         // C++0x: 7.2p2: opaque-enum-declaration.
         // Conflicts are diagnosed above. Do nothing.
       }
       else if (PrevDecl && (Def = cast<EnumDecl>(PrevDecl)->getDefinition())) {
         Diag(Loc, diag::ext_forward_ref_enum_def)
           << New;
         Diag(Def->getLocation(), diag::note_previous_definition);

test/SemaCXX/MicrosoftCompatibility-cxx98.cpp

-// RUN: %clang_cc1 %s -triple i686-pc-win32 -fsyntax-only -std=c++98 -Wmicrosoft -verify -fms-compatibility -fexceptions -fcxx-exceptions
-
-
-//MSVC allows forward enum declaration
-enum ENUM; // expected-warning {{forward references to 'enum' types are a Microsoft extension}}
-ENUM *var = 0;     
-ENUM var2 = (ENUM)3;
-enum ENUM1* var3 = 0;// expected-warning {{forward references to 'enum' types are a Microsoft extension}}
-
-typedef void (*FnPtrTy)();
-void (*PR23733_1)() = static_cast<FnPtrTy>((void *)0); // expected-warning {{static_cast between pointer-to-function and pointer-to-object is a Microsoft extension}}
-void (*PR23733_2)() = FnPtrTy((void *)0);
-void (*PR23733_3)() = (FnPtrTy)((void *)0);
-void (*PR23733_4)() = reinterpret_cast<FnPtrTy>((void *)0);
-
-long function_prototype(int a);
-long (*function_ptr)(int a);
-
-void function_to_voidptr_conv() {
-  void *a1 = function_prototype;  // expected-warning {{implicit conversion between pointer-to-function and pointer-to-object is a Microsoft extension}}
-  void *a2 = &function_prototype; // expected-warning {{implicit conversion between pointer-to-function and pointer-to-object is a Microsoft extension}}
-  void *a3 = function_ptr;        // expected-warning {{implicit conversion between pointer-to-function and pointer-to-object is a Microsoft extension}}
-}

test/SemaCXX/MicrosoftCompatibility.cpp

 {
     const T::Type var = 2; // expected-warning {{missing 'typename' prior to dependent type name}}
 }
 
 template void function_missing_typename<D>(const D::Type param);
 
 }
 
+//MSVC allows forward enum declaration
+enum ENUM; // expected-warning {{forward references to 'enum' types are a Microsoft extension}}
+ENUM *var = 0;     
+ENUM var2 = (ENUM)3;
+enum ENUM1* var3 = 0;// expected-warning {{forward references to 'enum' types are a Microsoft extension}}
+
+enum ENUM1 { kA };
+enum ENUM1;  // This way round is fine.
+
 enum ENUM2 {
   ENUM2_a = (enum ENUM2) 4,
   ENUM2_b = 0x9FFFFFFF, // expected-warning {{enumerator value is not representable in the underlying type 'int'}}
   ENUM2_c = 0x100000000 // expected-warning {{enumerator value is not representable in the underlying type 'int'}}
 };
 
 
 namespace PR11791 {

 void f(int);
 void g() {
   // This is an ambiguous call in standard C++.
   // This calls f(long long) in Microsoft mode because LL is always signed.
   f(0xffffffffffffffffLL);
   f(0xffffffffffffffffi64);
 }
 }
+
+typedef void (*FnPtrTy)();
+void (*PR23733_1)() = static_cast<FnPtrTy>((void *)0); // expected-warning {{static_cast between pointer-to-function and pointer-to-object is a Microsoft extension}}
+void (*PR23733_2)() = FnPtrTy((void *)0);
+void (*PR23733_3)() = (FnPtrTy)((void *)0);
+void (*PR23733_4)() = reinterpret_cast<FnPtrTy>((void *)0);
+
+long function_prototype(int a);
+long (*function_ptr)(int a);
+
+void function_to_voidptr_conv() {
+  void *a1 = function_prototype;  // expected-warning {{implicit conversion between pointer-to-function and pointer-to-object is a Microsoft extension}}
+  void *a2 = &function_prototype; // expected-warning {{implicit conversion between pointer-to-function and pointer-to-object is a Microsoft extension}}
+  void *a3 = function_ptr;        // expected-warning {{implicit conversion between pointer-to-function and pointer-to-object is a Microsoft extension}}
+}