[Clang] Modify CXXMethodDecl::isMoveAssignmentOperator() to look through type sugar

AcceptedPublic

Currently CXXMethodDecl::isMoveAssignmentOperator() does not look though type
sugar and so if the parameter is a type alias it will not be able to detect
that the method is a move assignment operator. This PR fixes that and adds a set
of tests that covers that we correctly detect special member functions when
defaulting or deleting them.

This fixes: https://github.com/llvm/llvm-project/issues/56456

Differential Revision: https://reviews.llvm.org/D129591

clang/docs/ReleaseNotes.rst

@@ -186,6 +186,8 @@ Bug Fixes
 - Clang now checks ODR violations when merging concepts from different modules.
   Note that this may possibly break existing code, and is done so intentionally.
   Fixes `Issue 56310 <https://github.com/llvm/llvm-project/issues/56310>`_.
+- Clang will now look through type sugar when checking a member function is a
+  move assignment operator. Fixes `Issue 56456 <https://github.com/llvm/llvm-project/issues/56456>`_.
 
 Improvements to Clang's diagnostics
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/AST/DeclCXX.cpp

@@ -2410,7 +2410,7 @@ bool CXXMethodDecl::isMoveAssignmentOperator() const {
     return false;
 
   QualType ParamType = getParamDecl(0)->getType();
-  if (!isa<RValueReferenceType>(ParamType))
+  if (!ParamType->isRValueReferenceType())
     return false;
   ParamType = ParamType->getPointeeType();
 

clang/test/SemaCXX/cxx0x-defaulted-functions.cpp

@@ -259,3 +259,28 @@ namespace P1286R2 {
 
   static_assert(noexcept(A::B()), "");
 }
+
+namespace GH56456 {
+template <typename T>
+using RC=T const&;
+template <typename T>
+using RV=T&;
+template <typename T>
+using RM=T&&;
+
+struct A {
+  A(RC<A>) = default;
+  A(RM<A>) = default;
+
+  auto operator=(RC<A>) -> RV<A> = default;
+  auto operator=(RM<A>) -> RV<A> = default;
+};
+
+struct B {
+  B (RC<B>) = delete;
+  B (RM<B>) = delete;
+
+  auto operator = (RC<B>) -> RV<B> = delete;
+  auto operator = (RM<B>) -> RV<B> = delete;
+};
+}