https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121940
--- Comment #3 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Tomasz Kaminski <tkami...@gcc.gnu.org>: https://gcc.gnu.org/g:7dd28f0a815cdaf52b6f8f6039cabfde256aacc1 commit r16-4059-g7dd28f0a815cdaf52b6f8f6039cabfde256aacc1 Author: Tomasz KamiÅski <tkami...@redhat.com> Date: Tue Sep 23 08:54:28 2025 +0200 libstdc++: Make function_ref(nontype<f>, r) CTAD SFINAE friendly [PR121940] Instantiating the __deduce_funcref function body for function pointers without arguments or member pointers with non-matching object types previously led to hard errors due to the formation of invalid types. The __deduce_funcref function is now adjusted to return void in such cases. The corresponding function_ref deduction guide is constrained to only match if the return type is not void, making it SFINAE friendly. PR libstdc++/121940 libstdc++-v3/ChangeLog: * include/bits/funcwrap.h (__polyfunc::__deduce_funcref): Return void for ill-formed constructs. (function_ref(nontype_t<__f>, _Tp&&)): Constrain on __deduce_funcref producing non-void results. * testsuite/20_util/function_ref/deduction.cc: Negative tests. Reviewed-by: Jonathan Wakely <jwak...@redhat.com> Signed-off-by: Tomasz KamiÅski <tkami...@redhat.com>
