https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102529
--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The trunk branch has been updated by Jason Merrill <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:afe1f0c251d0429069c2414d4f3f14042efc174f commit r13-6556-gafe1f0c251d0429069c2414d4f3f14042efc174f Author: Jason Merrill <ja...@redhat.com> Date: Thu Feb 9 12:58:35 2023 -0800 c++: CTAD for less-specialized alias template [PR102529] The standard was unclear what happens with the transformation of a deduction guide if the initial template argument deduction fails for a reason other than not deducing all the arguments; my implementation assumed that the right thing was to give up on the deduction guide. But in consideration of CWG2664 this week I realized that we get a better result by just continuing with an empty set of deductions, so the alias deduction guide is the same as the original deduction guide plus the deducible constraint. DR 2664 PR c++/102529 gcc/cp/ChangeLog: * pt.cc (alias_ctad_tweaks): Continue after deduction failure. gcc/testsuite/ChangeLog: * g++.dg/DRs/dr2664.C: New test. * g++.dg/cpp2a/class-deduction-alias15.C: New test.
