https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119379
--- Comment #4 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:df5fa3a3d0d7f2413c832548c88f76dfe67802fd commit r15-8671-gdf5fa3a3d0d7f2413c832548c88f76dfe67802fd Author: Patrick Palka <ppa...@redhat.com> Date: Sat Mar 22 10:15:52 2025 -0400 c++: structural equality and partially inst typedef [PR119379] Complex alias templates (and their dependent specializations) always use structural equality because we need to treat them as transparent in some contexts but not others. Structural-ness however wasn't being preserved during partial instantiation, which for the below testcase leads to the checking ICE same canonical type node for different types 'S<int>::P<U>' and 'pair<int, U>' when comparing those two types with comparing_dependent_aliases set (from alias_ctad_tweaks). This patch fixes this by making us preserve structural-ness for partially instantiated typedefs in general. PR c++/119379 gcc/cp/ChangeLog: * pt.cc (tsubst_decl) <case TYPE_DECL>: Preserve structural-ness of a partially instantiated typedef. gcc/testsuite/ChangeLog: * g++.dg/cpp2a/class-deduction-alias24.C: New test. Reviewed-by: Jason Merrill <ja...@redhat.com>
