[clang] [clang][AST] Fix assertion in `getFullyQualifiedType` for AutoType (PR #186105)

[Harald van Dijk via cfe-commits]

hvdijk wrote:

It turns out that both this and `DecltypeType` are handled already by `getCanonicalType()`, which we call already but then drop its result. If we continue using it, and revert your code changes but keep your tests, those tests pass:
```diff
--- a/clang/lib/Interpreter/InterpreterValuePrinter.cpp
+++ b/clang/lib/Interpreter/InterpreterValuePrinter.cpp
@@ -78,7 +78,7 @@ static std::string QualTypeToString(ASTContext &Ctx, QualType QT) {
       !NonRefTy->isMemberPointerType())
     return Canon.getAsString(Ctx.getPrintingPolicy());

-  if (const auto *TDTy = dyn_cast<TypedefType>(NonRefTy)) {
+  if (const auto *TDTy = dyn_cast<TypedefType>(Canon)) {
     // FIXME: TemplateSpecializationType & SubstTemplateTypeParmType checks
     // are predominately to get STL containers to print nicer and might be
     // better handled in GetFullyQualifiedName.
@@ -90,10 +90,10 @@ static std::string QualTypeToString(ASTContext &Ctx, QualType QT) {
     if (llvm::isa<SubstTemplateTypeParmType>(SSDesugar))
       return GetFullTypeName(Ctx, Canon);
     else if (llvm::isa<TemplateSpecializationType>(SSDesugar))
-      return GetFullTypeName(Ctx, NonRefTy);
-    return DeclTypeToString(NonRefTy, TDTy->getDecl());
+      return GetFullTypeName(Ctx, Canon);
+    return DeclTypeToString(Canon, TDTy->getDecl());
   }
-  return GetFullTypeName(Ctx, NonRefTy);
+  return GetFullTypeName(Ctx, Canon);
 }

 static std::string EnumToString(const Value &V) {
``` 
Would you be able to see if this also works for what you found with `UnaryTransformType` ?

https://github.com/llvm/llvm-project/pull/186105