[Bug c++/124096] [reflection] bit_cast with consteval-only types should be rejected

[mpolacek at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124096

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Blocks|                            |123615
           Assignee|unassigned at gcc dot gnu.org      |mpolacek at gcc dot 
gnu.org
           Keywords|                            |accepts-invalid
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2026-02-13

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Maybe we want:

--- a/libstdc++-v3/include/std/bit
+++ b/libstdc++-v3/include/std/bit
@@ -93,6 +93,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       && is_trivially_copyable_v<_To> && is_trivially_copyable_v<_From>
 #endif
     {
+#if __cpp_impl_reflection >= 202506L
+      static_assert(!is_consteval_only_v<_To> && !is_consteval_only_v<_From>,
+           "neither To nor From can be consteval-only types");
+#endif
       return __builtin_bit_cast(_To, __from);
     }
 #endif // __cpp_lib_bit_cast


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123615
[Bug 123615] (c++-reflection) - [meta-bug] reflection issue