[clang] do not emit note for bad conversion when destination type qualifiers don't compatibly include source type qualifiers

[zequanwu]

Summary

llvm.org/PR52014

[rsmith]

Thanks! Would it be worth also including a testcase where the from and to types are different classes but the qualifications are incompatible, to ensure we're handling that case too?

[zequanwu]

Add a testcase that from and to type are differ and qualification are incompatible.

clang/lib/Sema/SemaInit.cpp

if (destType.getNonReferenceType()->isObjCObjectPointerType() &&
     S.EmitRelatedResultTypeNote(op);
 
     // Emit a possible note about a return failing because we're
     // expecting a related result type.
     if (entity.getKind() == InitializedEntity::EK_Result)
       S.EmitRelatedResultTypeNoteForReturn(destType);
   }
   QualType fromType = op->getType();
-  auto *fromDecl = fromType.getTypePtr()->getPointeeCXXRecordDecl();
-  auto *destDecl = destType.getTypePtr()->getPointeeCXXRecordDecl();
+  QualType fromPointeeType = fromType.getCanonicalType()->getPointeeType();
+  QualType destPointeeType = destType.getCanonicalType()->getPointeeType();
+  auto *fromDecl = fromType->getPointeeCXXRecordDecl();
+  auto *destDecl = destType->getPointeeCXXRecordDecl();
   if (fromDecl && destDecl && fromDecl->getDeclKind() == Decl::CXXRecord &&
       destDecl->getDeclKind() == Decl::CXXRecord &&
       !fromDecl->isInvalidDecl() && !destDecl->isInvalidDecl() &&
-      !fromDecl->hasDefinition())
+      !fromDecl->hasDefinition() &&
+      destPointeeType.getQualifiers().compatiblyIncludes(
+          fromPointeeType.getQualifiers()))
     S.Diag(fromDecl->getLocation(), diag::note_forward_class_conversion)
         << S.getASTContext().getTagDeclType(fromDecl)
         << S.getASTContext().getTagDeclType(destDecl);
 }
 
 static void diagnoseListInit(Sema &S, const InitializedEntity &Entity,
                              InitListExpr *InitList) {
   QualType DestType = Entity.getType();

clang/test/SemaCXX/pointer-forward-declared-class-conversion.cpp

 // RUN: %clang_cc1 -fsyntax-only -verify %s
 
 class A1 {};
 class B1; // expected-note{{'B1' is not defined, but forward declared here; conversion would be valid if it was derived from 'A1'}}
 B1 *b1;
 A1 *a1 = b1; // expected-error{{cannot initialize a variable of type 'A1 *' with an lvalue of type 'B1 *'}}
 
 template <class C> class A2 {};
 template <class C> class B2;
 B2<int> *b2;
 A2<int> *a2 = b2; // expected-error{{cannot initialize a variable of type 'A2<int> *' with an lvalue of type 'B2<int> *'}}
+
+typedef struct S s;
+const s *f();
+s *g1() { return f(); } // expected-error{{cannot initialize return object of type 's *' (aka 'S *') with an rvalue of type 'const s *' (aka 'const S *')}}
+
+B1 *g2() { return f(); } // expected-error{{cannot initialize return object of type 'B1 *' with an rvalue of type 'const s *' (aka 'const S *')}}
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