[clang] [clang] Add test for CWG170 "Pointer-to-member conversions" (PR #121667)

[Vlad Serebrennikov via cfe-commits]

https://github.com/Endilll created https://github.com/llvm/llvm-project/pull/121667

This patch adds test for [CWG170](https://cplusplus.github.io/CWG/issues/170.html). The resolution adds explicit undefined behavior, so I think the best we can do is to put the test into constexpr evaluator. Change to [expr.static.cast] is not tested, because it was a drive-by fix that removed an impossible case (I confirmed it using minutes). Minutes mention several times a comprehensive paper in this design space which no one seem to remember. I believe it's [P0149R0](https://wg21.link/p0149r0) "Generalised member pointers".

>From ec44a719b7b2dc2e9ac13e1d4d18e7d93337ca69 Mon Sep 17 00:00:00 2001
From: Vlad Serebrennikov <serebrennikov.vladislav at gmail.com>
Date: Sun, 5 Jan 2025 00:08:34 +0300
Subject: [PATCH] [clang] Add test for CWG170 "Pointer-to-member conversions"

---
 clang/test/CXX/drs/cwg1xx.cpp | 20 ++++++++++++++++++++
 clang/www/cxx_dr_status.html  |  2 +-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/clang/test/CXX/drs/cwg1xx.cpp b/clang/test/CXX/drs/cwg1xx.cpp
index 6aec8b65c91f12..0110c711d6dd89 100644
--- a/clang/test/CXX/drs/cwg1xx.cpp
+++ b/clang/test/CXX/drs/cwg1xx.cpp
@@ -1074,6 +1074,26 @@ namespace cwg169 { // cwg169: yes
   };
 }
 
+namespace cwg170 { // cwg170: 3.1
+#if __cplusplus >= 201103L
+struct A {};
+struct B : A { int i; };
+struct C : A {};
+struct D : C {};
+
+constexpr int f(int A::*) { return 0; }
+constexpr int g(int C::*) { return 0; }
+constexpr int h(int D::*) { return 0; }
+
+constexpr auto p = static_cast<int A::*>(&B::i);
+constexpr auto q = f(p);
+constexpr auto r = g(p);
+// since-cxx11-error at -1 {{constexpr variable 'r' must be initialized by a constant expression}}
+constexpr auto s = h(p);
+// since-cxx11-error at -1 {{constexpr variable 's' must be initialized by a constant expression}}
+#endif
+} // namespace cwg170
+
 namespace { // cwg171: 3.4
   int cwg171a;
 }
diff --git a/clang/www/cxx_dr_status.html b/clang/www/cxx_dr_status.html
index c069e155fd547c..935411e778b251 100755
--- a/clang/www/cxx_dr_status.html
+++ b/clang/www/cxx_dr_status.html
@@ -1065,7 +1065,7 @@ <h2 id="cxxdr">C++ defect report implementation status</h2>
     <td><a href="https://cplusplus.github.io/CWG/issues/170.html">170</a></td>
     <td>DRWP</td>
     <td>Pointer-to-member conversions</td>
-    <td class="unknown" align="center">Unknown</td>
+    <td class="full" align="center">Clang 3.1</td>
   </tr>
   <tr id="171">
     <td><a href="https://cplusplus.github.io/CWG/issues/171.html">171</a></td>