MS ABI: Mangle alias templates used as template-template arguments

A templated using declaration may be used as a template-template
argument.

Unfortunately, the VS "14" chooses '?' as the sole marker for the
argument.  This is problematic because it presupposes the possibility of
using more than one template-aliases as arguments to the same template.

This fixes PR20047.

llvm-svn: 214290

1 files changed, 13 insertions, 3 deletions

diff --git a/clang/lib/AST/MicrosoftMangle.cpp b/clang/lib/AST/MicrosoftMangle.cpp
index e6a6d09b484..0c80ff814c7 100644
--- a/clang/lib/AST/MicrosoftMangle.cpp
+++ b/clang/lib/AST/MicrosoftMangle.cpp
@@ -1179,11 +1179,21 @@ void MicrosoftCXXNameMangler::mangleTemplateArg(const TemplateDecl *TD,
     }
     break;
   }
-  case TemplateArgument::Template:
-    mangleType(cast<TagDecl>(
-        TA.getAsTemplate().getAsTemplateDecl()->getTemplatedDecl()));
+  case TemplateArgument::Template: {
+    const NamedDecl *ND =
+        TA.getAsTemplate().getAsTemplateDecl()->getTemplatedDecl();
+    if (const auto *TD = dyn_cast<TagDecl>(ND)) {
+      mangleType(TD);
+    } else if (isa<TypeAliasDecl>(ND)) {
+      // FIXME: The mangling, while compatible with VS "14", is horribly
+      // broken.  Update this when they release their next compiler.
+      Out << '?';
+    } else {
+      llvm_unreachable("unexpected template template NamedDecl!");
+    }
     break;
   }
+  }
 }
 
 void MicrosoftCXXNameMangler::mangleQualifiers(Qualifiers Quals,