https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99180
--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-10 branch has been updated by Jason Merrill <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:92e9b2a995f718f1c2ab1cd0840b439c24d3535f commit r10-9852-g92e9b2a995f718f1c2ab1cd0840b439c24d3535f Author: Jason Merrill <ja...@redhat.com> Date: Fri Apr 9 18:02:38 2021 -0400 c++: deduction guide using alias [PR99180] alias_ctad_tweaks was expecting that all deduction guides for the class would be suitable for deduction from the alias definition; in this case, the deduction guide uses 'true' and the alias B uses 'false', so deduction fails. But that's OK, we just don't use that deduction guide. I also noticed that we were giving up on deduction entirely if substitution failed for some guide; we should only give up on that particular deduction guide. We ought to give a better diagnostic about this case when deduction fails, but that can wait. gcc/cp/ChangeLog: PR c++/99180 PR c++/93295 PR c++/93867 PR c++/99118 PR c++/96873 * pt.c (alias_ctad_tweaks): Handle failure better. gcc/testsuite/ChangeLog: PR c++/99180 PR c++/93295 PR c++/93867 PR c++/95486 * g++.dg/cpp2a/class-deduction-alias5.C: New test. * g++.dg/cpp2a/class-deduction-alias6.C: New test. * g++.dg/cpp2a/class-deduction-alias7.C: New test. * g++.dg/cpp2a/class-deduction-alias8.C: New test.
