[clang][docs] Reflect the implementation status for P2280R4

clang/test/SemaCXX/constant-expression-cxx11.cpp

@@ -2005,7 +2005,7 @@ namespace ConstexprConstructorRecovery {
   constexpr X x{}; // cxx11-error {{constant expression}} cxx11-note {{not initialized}}
 }
 
-namespace Lifetime {
+namespace Lifetime { // FIXME: Fix the error messages quality regression introduced by GH95474.
   void f() {
     constexpr int &n = n; // expected-error {{constant expression}} cxx23-note {{reference to 'n' is not a constant expression}} cxx23-note {{address of non-static constexpr variable 'n' may differ}} expected-warning {{not yet bound to a value}}
                           // cxx11_20-note@-1 {{use of reference outside its lifetime is not allowed in a constant expression}}
@@ -2421,7 +2421,7 @@ namespace PR41854 {
   unsigned b = d.c;
 }
 
-namespace array_size {
+namespace array_size { // FIXME: P2280R4 should be backported, and these cases should be accepted in C++11 and later.
   template<int N> struct array {
     static constexpr int size() { return N; }
   };

clang/test/SemaCXX/constant-expression-p2280r4.cpp

@@ -1,6 +1,8 @@
 // RUN: %clang_cc1 -std=c++23 -verify=expected,nointerpreter %s
 // RUN: %clang_cc1 -std=c++23 -verify %s -fexperimental-new-constant-interpreter
 
+// FIXME: P2280R4 should be backported. Run this in C++11 and later modes.
+
 using size_t = decltype(sizeof(0));
 
 namespace std {

clang/www/cxx_status.html

@@ -476,7 +476,7 @@ <h2 id="cxx23">C++23 implementation status</h2>
     <tr>
       <td>Using unknown pointers and references in constant expressions</td>
       <td><a href="https://wg21.link/P2280R4">P2280R4</a> (<a href="#dr">DR</a>)</td>
-      <td class="full" align="center">Clang 20</td>
+      <td class="full" align="center">Clang 20 <a href="#p2280">(12)</a></td>
     </tr>
     <tr>
       <td>static <code>operator()</code></td>
@@ -546,6 +546,11 @@ <h2 id="cxx23">C++23 implementation status</h2>
       <td class="full" align="center">Yes</td>
     </tr>
 </table>
+
+<p>
+<span id="p2280">(12): This feature is not yet available in C++20 and earlier modes.
+</span>
+</p>
 </details>