[Clang] fix overload resolution for object parameters with top-level cv-qualifiers in member functions

clang/docs/ReleaseNotes.rst

@@ -473,6 +473,7 @@ Bug Fixes to C++ Support
   containing outer unexpanded parameters were not correctly expanded. (#GH101754)
 - Fixed a bug in constraint expression comparison where the ``sizeof...`` expression was not handled properly
   in certain friend declarations. (#GH93099)
+- Fixed overload handling for object parameters with top-level cv-qualifiers in explicit member functions (#GH100394)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaOverload.cpp

@@ -1511,6 +1511,12 @@ static bool IsOverloadOrOverrideImpl(Sema &SemaRef, FunctionDecl *New,
       auto NewObjectType = New->getFunctionObjectParameterReferenceType();
       auto OldObjectType = Old->getFunctionObjectParameterReferenceType();
 
+      if (Old->isExplicitObjectMemberFunction() &&
+          OldObjectType.getQualifiers() != NewObjectType.getQualifiers())
+        return OldObjectType.isConstQualified() &&
+               (NewObjectType.isConstQualified() ||
+                NewObjectType.isVolatileQualified());
+
       auto IsImplicitWithNoRefQual = [](const CXXMethodDecl *F) {
         return F->getRefQualifier() == RQ_None &&
                !F->isExplicitObjectMemberFunction();

clang/test/SemaCXX/cxx2b-deducing-this.cpp

@@ -1073,3 +1073,16 @@ int main() {
   return foo[]; // expected-error {{no viable overloaded operator[] for type 'Foo'}}
 }
 }
+
+namespace GH100394 {
+struct C1 {
+  void f(this const C1);
+  void f() const;        // ok
+};
+
+struct C2 {
+  void f(this const C2);    // expected-note {{previous declaration is here}}
+  void f(this volatile C2); // expected-error {{class member cannot be redeclared}} \
+                            // expected-warning {{volatile-qualified parameter type 'volatile C2' is deprecated}}
+};
+}