[clang] member pointer class qualification fix (#142081)

This fixes a regression introduced in
#130537,
which was reported here:
#132401 (comment)

When deducing member pointers class, ignore top level qualifiers on the
argument side, since the class portion of a member pointer is a
nested-name-specifier, and these just nominate an entity.

Qualifiers on the parameter side are fine since deduction allows the
parameter side to be more qualified, and these qualifiers won't be part
of the result.

Since this regression was never released, there are no release notes.

Author: mizvekov

clang/lib/Sema/SemaTemplateDeduction.cpp

@@ -2127,7 +2127,7 @@ static TemplateDeductionResult DeduceTemplateArgumentsByTypeMatch(
         TA = S.Context.getTypeDeclType(MPA->getMostRecentCXXRecordDecl());
       } else {
         NestedNameSpecifier *QA = MPA->getQualifier();
-        TA = QualType(QA->translateToType(S.Context), 0);
+        TA = QualType(QA->translateToType(S.Context), 0).getUnqualifiedType();
       }
       assert(!TA.isNull() && "member pointer with non-type class");
       return DeduceTemplateArgumentsByTypeMatch(

clang/test/SemaCXX/member-pointer.cpp

@@ -408,3 +408,25 @@ namespace deduction2 {
     void i() { e(&C::h); }
   };
 } // namespace deduction2
+
+namespace deduction_qualifiers {
+  struct A {
+    int v;
+  };
+  using CA = const A;
+
+  template <class T> void g(const T&, int T::*);
+  template <class T> void h(const T&, int CA::*);
+
+  void test(const A a, A b) {
+    g(a, &A::v);
+    g(a, &CA::v);
+    h(a, &A::v);
+    h(a, &CA::v);
+
+    g(b, &A::v);
+    g(b, &CA::v);
+    h(b, &A::v);
+    h(b, &CA::v);
+  }
+} // namespace deduction_qualifiers