[SEMA] split ExtWarn dupl-decl-spec's into Extension and ExtWarn

[nickdesaulniers]

Summary

For types deduced from typedef's and typeof's, don't warn for duplicate
declaration specifiers in C90 unless -pedantic.

Create a third diagnostic type for duplicate declaration specifiers.
Previously, we had an ExtWarn and a Warning. This change adds a third,
Extension, which only warns when -pedantic is set, staying silent
otherwise.

Fixes PR32985.

[rsmith]

LGTM, thanks!

[nickdesaulniers]

Thanks for your suggestions and code review. I appreciate it.

cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td

 def err_designator_into_flexible_array_member : Error<
   "designator into flexible array member subobject">;
 def note_flexible_array_member : Note<
   "initialized flexible array member %0 is here">;
 def ext_flexible_array_init : Extension<
   "flexible array initialization is a GNU extension">, InGroup<GNUFlexibleArrayInitializer>;
 
 // Declarations.
-def ext_duplicate_declspec : ExtWarn<"duplicate '%0' declaration specifier">,
+def ext_duplicate_declspec : Extension<"duplicate '%0' declaration specifier">,
+  InGroup<DuplicateDeclSpecifier>;
+def ext_warn_duplicate_declspec : ExtWarn<"duplicate '%0' declaration specifier">,
   InGroup<DuplicateDeclSpecifier>;
 def warn_duplicate_declspec : Warning<"duplicate '%0' declaration specifier">,
   InGroup<DuplicateDeclSpecifier>;
 def ext_plain_complex : ExtWarn<
   "plain '_Complex' requires a type specifier; assuming '_Complex double'">;
 def ext_imaginary_constant : Extension<
   "imaginary constants are a GNU extension">, InGroup<GNUImaginaryConstant>;
 def ext_integer_complex : Extension<

cfe/trunk/lib/Parse/ParseDecl.cpp

case tok::less:
       // If a type specifier follows, it will be diagnosed elsewhere.
       continue;
     }
     // If the specifier wasn't legal, issue a diagnostic.
     if (isInvalid) {
       assert(PrevSpec && "Method did not return previous specifier!");
       assert(DiagID);
 
-      if (DiagID == diag::ext_duplicate_declspec)
+      if (DiagID == diag::ext_duplicate_declspec ||
+          DiagID == diag::ext_warn_duplicate_declspec)
         Diag(Tok, DiagID)
           << PrevSpec << FixItHint::CreateRemoval(Tok.getLocation());
       else if (DiagID == diag::err_opencl_unknown_type_specifier) {
         Diag(Tok, DiagID) << getLangOpts().OpenCLCPlusPlus
             << getLangOpts().getOpenCLVersionTuple().getAsString()
             << PrevSpec << isStorageClass;
       } else
         Diag(Tok, DiagID) << PrevSpec;

cfe/trunk/lib/Sema/DeclSpec.cpp

 template <class T> static bool BadSpecifier(T TNew, T TPrev,
                                             const char *&PrevSpec,
                                             unsigned &DiagID,
                                             bool IsExtension = true) {
   PrevSpec = DeclSpec::getSpecifierName(TPrev);
   if (TNew != TPrev)
     DiagID = diag::err_invalid_decl_spec_combination;
   else
-    DiagID = IsExtension ? diag::ext_duplicate_declspec :
+    DiagID = IsExtension ? diag::ext_warn_duplicate_declspec :
                            diag::warn_duplicate_declspec;
   return true;
 }
 
 const char *DeclSpec::getSpecifierName(DeclSpec::SCS S) {
   switch (S) {
   case DeclSpec::SCS_unspecified: return "unspecified";
   case DeclSpec::SCS_typedef:     return "typedef";
bool DeclSpec::SetFriendSpec(SourceLocation Loc, const char *&PrevSpec,
   FriendLoc = Loc;
   return false;
 }
 
 bool DeclSpec::setModulePrivateSpec(SourceLocation Loc, const char *&PrevSpec,
                                     unsigned &DiagID) {
   if (isModulePrivateSpecified()) {
     PrevSpec = "__module_private__";
-    DiagID = diag::ext_duplicate_declspec;
+    DiagID = diag::ext_warn_duplicate_declspec;
     return true;
   }
 
   ModulePrivateLoc = Loc;
   return false;
 }
 
 bool DeclSpec::SetConstexprSpec(SourceLocation Loc, const char *&PrevSpec,

cfe/trunk/test/Sema/pr32985.c

+/*
+RUN: %clang_cc1 %s -std=gnu89 -fsyntax-only 2>&1 | FileCheck -check-prefix=CHECK-GNU89 %s -allow-empty
+RUN: %clang_cc1 %s -std=gnu89 -pedantic -fsyntax-only 2>&1 | FileCheck -check-prefix=CHECK-GNU89-PEDANTIC %s
+*/
+
+typedef const int t;
+const t c_i;
+/*
+CHECK-GNU89-NOT: 7:1: warning: duplicate 'const' declaration specifier
+CHECK-GNU89-PEDANTIC: 7:1: warning: duplicate 'const' declaration specifier
+*/
+
+const int c_i2;
+const typeof(c_i2) c_i3;
+/*
+CHECK-GNU89-NOT: 14:7: warning: extension used
+CHECK-GNU89-NOT: 14:1: warning: duplicate 'const' declaration specifier
+CHECK-GNU89-PEDANTIC: 14:7: warning: extension used
+CHECK-GNU89-PEDANTIC: 14:1: warning: duplicate 'const' declaration specifier
+*/