https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118626
--- Comment #11 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:58c5055162b698dab6a493b1f90c18af1a34ac65 commit r15-9230-g58c5055162b698dab6a493b1f90c18af1a34ac65 Author: Patrick Palka <ppa...@redhat.com> Date: Sat Apr 5 22:39:12 2025 -0400 c++: maybe_dependent_member_ref and stripped alias [PR118626] Here during maybe_dependent_member_ref (as part of CTAD rewriting for the variant constructor) for __accepted_type<_Up> we strip this alias all the way to type _Nth_type<__accepted_index<_Up>>, for which we return NULL since _Nth_type is at namespace scope and so no longer needs rewriting. Note that however the template argument __accepted_index<_Up> of this stripped type _does_ need rewriting (since it specializes a variable template from the current instantiation). We end up not rewriting this variable template reference at any point however because upon returning NULL, the caller (tsubst) proceeds to substitute the original form of the type __accepted_type<_Up>, which doesn't directly refer to __accepted_index. This later leads to an ICE during subsequent alias CTAD rewriting of this guide that contains a non-rewritten reference to __accepted_index. So when maybe_dependent_member_ref decides to not rewrite a class-scope alias that's been stripped, the caller needs to commit to substituting the stripped type rather than the original type. This patch essentially implements that by making maybe_dependent_member_ref call tsubst itself in that case. PR c++/118626 gcc/cp/ChangeLog: * pt.cc (maybe_dependent_member_ref): Substitute and return the stripped type if we decided to not rewrite it directly. gcc/testsuite/ChangeLog: * g++.dg/cpp2a/class-deduction-alias25.C: New test. Reviewed-by: Jason Merrill <ja...@redhat.com>
