[clang] [clang-tools-extra] [Attributes][HLSL] Teach EnumArgument to refer to an external enum (PR #70835)

[Erich Keane via cfe-commits]

================
@@ -1010,14 +1022,17 @@ namespace {
       // trivial because some enumeration values have multiple named
       // enumerators, such as type_visibility(internal) and
       // type_visibility(hidden) both mapping to TypeVisibilityAttr::Hidden.
-      OS << "const char *" << getAttrName() << "Attr::Convert" << type
-         << "ToStr(" << type << " Val) {\n"
+      OS << "const char *" << getAttrName() << "Attr::Convert" << shortType
+         << "ToStr(" << fullType << " Val) {\n"
          << "  switch(Val) {\n";
       SmallDenseSet<StringRef, 8> Uniques;
       for (size_t I = 0; I < enums.size(); ++I) {
         if (Uniques.insert(enums[I]).second)
-          OS << "  case " << getAttrName() << "Attr::" << enums[I]
-             << ": return \"" << values[I] << "\";\n";
+          OS << "  case " << fullType << "::" << enums[I] << ": return \""
+             << values[I] << "\";\n";
+      }
+      if (isExternal) {
+        OS << "  default: llvm_unreachable(\"Invalid attribute value\");\n";
----------------
erichkeane wrote:

Could you please provide an excerpt from of `Attr.inc` for me that shows what the external looks like here?  I'm having a bit of a hassle figuring out what allt he changes you've made are doing.

https://github.com/llvm/llvm-project/pull/70835