[clang] fix structural comparison for dependent class member pointer (#133343)

Fixes a regression introduced in
llvm/llvm-project#130537 and reported here
llvm/llvm-project#133144

This fixes a crash in ASTStructuralEquivalence where the non-null
precondition for IsStructurallyEquivalent would be violated, when
comparing member pointers with a dependent class.

This also drive-by fixes the ast node traverser for member pointers so
it doesn't traverse into the qualifier in case it's not a type, or the
class declaration in case it would be equivalent to what the qualifier
refers.

This avoids printing of `<<<NULL>>>` on the text node dumper, which is
redundant.

No release notes since the regression was never released.

Fixes llvm/llvm-project#133144

Author: mizvekov

clang/include/clang/AST/ASTNodeTraverser.h

@@ -394,8 +394,13 @@ class ASTNodeTraverser
   }
   void VisitMemberPointerType(const MemberPointerType *T) {
     // FIXME: Provide a NestedNameSpecifier visitor.
-    Visit(T->getQualifier()->getAsType());
-    Visit(T->getMostRecentCXXRecordDecl());
+    NestedNameSpecifier *Qualifier = T->getQualifier();
+    if (NestedNameSpecifier::SpecifierKind K = Qualifier->getKind();
+        K == NestedNameSpecifier::TypeSpec ||
+        K == NestedNameSpecifier::TypeSpecWithTemplate)
+      Visit(Qualifier->getAsType());
+    if (T->isSugared())
+      Visit(T->getMostRecentCXXRecordDecl()->getTypeForDecl());
     Visit(T->getPointeeType());
   }
   void VisitArrayType(const ArrayType *T) { Visit(T->getElementType()); }

clang/lib/AST/ASTStructuralEquivalence.cpp

@@ -897,9 +897,11 @@ static bool IsStructurallyEquivalent(StructuralEquivalenceContext &Context,
     if (!IsStructurallyEquivalent(Context, MemPtr1->getQualifier(),
                                   MemPtr2->getQualifier()))
       return false;
-    if (!IsStructurallyEquivalent(Context,
-                                  MemPtr1->getMostRecentCXXRecordDecl(),
-                                  MemPtr2->getMostRecentCXXRecordDecl()))
+    CXXRecordDecl *D1 = MemPtr1->getMostRecentCXXRecordDecl(),
+                  *D2 = MemPtr2->getMostRecentCXXRecordDecl();
+    if (D1 == D2)
+      break;
+    if (!D1 || !D2 || !IsStructurallyEquivalent(Context, D1, D2))
       return false;
     break;
   }

clang/test/AST/ast-dump-template-json-win32-mangler-crash.cpp

@@ -2452,9 +2452,6 @@ int main()
 // CHECK-NEXT:          }
 // CHECK-NEXT:         },
 // CHECK-NEXT:         {
-// CHECK-NEXT:          "id": "0x0"
-// CHECK-NEXT:         },
-// CHECK-NEXT:         {
 // CHECK-NEXT:          "id": "0x{{.*}}",
 // CHECK-NEXT:          "kind": "TemplateTypeParmType",
 // CHECK-NEXT:          "type": {