[clang] p1099 using enum part 2

This implements the 'using enum maybe-qualified-enum-tag ;' part of
1099. It introduces a new 'UsingEnumDecl', subclassed from
'BaseUsingDecl'. Much of the diff is the boilerplate needed to get the
new class set up.

There is one case where we accept ill-formed, but I believe this is
merely an extended case of an existing bug, so consider it
orthogonal. AFAICT in class-scope the c++20 rule is that no 2 using
decls can bring in the same target decl ([namespace.udecl]/8). But we
already accept:

struct A { enum { a }; };
struct B : A { using A::a; };
struct C : B { using A::a;
using B::a; }; // same enumerator

this patch permits mixtures of 'using enum Bob;' and 'using Bob::member;' in the same way.

Differential Revision: https://reviews.llvm.org/D102241

1 files changed, 4 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index c93339a211f3..7efc97c51eda 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -5740,6 +5740,10 @@ void CodeGenModule::EmitTopLevelDecl(Decl *D) {
     if (CGDebugInfo *DI = getModuleDebugInfo())
         DI->EmitUsingDecl(cast<UsingDecl>(*D));
     break;
+  case Decl::UsingEnum: // using enum X; [C++]
+    if (CGDebugInfo *DI = getModuleDebugInfo())
+      DI->EmitUsingEnumDecl(cast<UsingEnumDecl>(*D));
+    break;
   case Decl::NamespaceAlias:
     if (CGDebugInfo *DI = getModuleDebugInfo())
         DI->EmitNamespaceAlias(cast<NamespaceAliasDecl>(*D));