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

[Matheus Izvekov via cfe-commits]

https://github.com/mizvekov created https://github.com/llvm/llvm-project/pull/142081

This fixes a regression introduced in https://github.com/llvm/llvm-project/pull/130537,
which was reported here: https://github.com/llvm/llvm-project/pull/132401#issuecomment-2839690599

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.

>From 12f4283d7692b44757103e15146b863cd3e8b023 Mon Sep 17 00:00:00 2001
From: Matheus Izvekov <mizvekov at gmail.com>
Date: Thu, 29 May 2025 23:31:50 -0300
Subject: [PATCH] [clang] member pointer class qualification fix

This fixes a regression introduced in https://github.com/llvm/llvm-project/pull/130537

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.
---
 clang/lib/Sema/SemaTemplateDeduction.cpp |  2 +-
 clang/test/SemaCXX/member-pointer.cpp    | 22 ++++++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/clang/lib/Sema/SemaTemplateDeduction.cpp b/clang/lib/Sema/SemaTemplateDeduction.cpp
index 51bfca9da4231..5566057cccef8 100644
--- a/clang/lib/Sema/SemaTemplateDeduction.cpp
+++ b/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(
diff --git a/clang/test/SemaCXX/member-pointer.cpp b/clang/test/SemaCXX/member-pointer.cpp
index c94c26fbcbb28..6bb0686be7403 100644
--- a/clang/test/SemaCXX/member-pointer.cpp
+++ b/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