[MSVC Compat] Try to treat an implicit, fixed enum as an unfixed enum

consider the following:
enum E *p;
enum E { e };

The above snippet is not ANSI C because 'enum E' has not bee defined
when we are processing the declaration of 'p'; however, it is a popular
extension to make the above work.  This would fail using the Microsoft
enum semantics because the definition of 'E' would implicitly have a
fixed underlying type of 'int' which would trigger diagnostic messages
about a mismatch between the declaration and the definition.

Instead, treat fixed underlying types as not fixed for the purposes of
the diagnostic.

llvm-svn: 249674

1 files changed, 2 insertions, 1 deletions

diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 029af186fdc..1789855c40f 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -835,7 +835,8 @@ Decl *TemplateDeclInstantiator::VisitEnumDecl(EnumDecl *D) {
         SemaRef.SubstType(TI->getType(), TemplateArgs,
                           UnderlyingLoc, DeclarationName());
       SemaRef.CheckEnumRedeclaration(Def->getLocation(), Def->isScoped(),
-                                     DefnUnderlying, Enum);
+                                     DefnUnderlying,
+                                     /*EnumUnderlyingIsImplicit=*/false, Enum);
     }
   }