[clang] [clang-tools-extra] [clang] [Sema] Preserve nested name specifier prefix in MemberPointerType (PR #118236)

[Matheus Izvekov via cfe-commits]

================
@@ -5347,13 +5347,16 @@ static TypeSourceInfo *GetFullTypeForDeclarator(TypeProcessingState &state,
 
         case NestedNameSpecifier::TypeSpec:
         case NestedNameSpecifier::TypeSpecWithTemplate:
-          ClsType = QualType(NNS->getAsType(), 0);
+          const Type *NNSType = NNS->getAsType();
+          ClsType = QualType(NNSType, 0);
           // Note: if the NNS has a prefix and ClsType is a nondependent
-          // TemplateSpecializationType, then the NNS prefix is NOT included
-          // in ClsType; hence we wrap ClsType into an ElaboratedType.
-          // NOTE: in particular, no wrap occurs if ClsType already is an
-          // Elaborated, DependentName, or DependentTemplateSpecialization.
-          if (isa<TemplateSpecializationType>(NNS->getAsType()))
+          // TemplateSpecializationType or a RecordType, then the NNS prefix is
+          // NOT included in ClsType; hence we wrap ClsType into an
+          // ElaboratedType. NOTE: in particular, no wrap occurs if ClsType
+          // already is an Elaborated, DependentName, or
+          // DependentTemplateSpecialization.
+          if (isa<TemplateSpecializationType>(NNSType) ||
+              (NNSPrefix && isa<RecordType>(NNSType)))
----------------
mizvekov wrote:

It would also be cool to have an assertion here, that we are handling all cases.

I think the logic here would be something like:
```
if (isa<DependentTemplateSpecializationType>...)
  // Rebuild DependentTemplateSpecializationType, adding the Prefix.
else
  // either the dependent case (TemplateSpecializationType), or the non-dependent one (RecordType).
 // assert(isa<TemplateSpecializationType, RecordType>...)
``` 

https://github.com/llvm/llvm-project/pull/118236