https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93286
--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jason Merrill <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:5194b51ed9714808d88827531e91474895b6c706 commit r10-6029-g5194b51ed9714808d88827531e91474895b6c706 Author: Jason Merrill <ja...@redhat.com> Date: Thu Jan 16 16:55:39 2020 -0500 PR c++/93286 - ICE with __is_constructible and variadic template. Here we had been recursing in tsubst_copy_and_build if type2 was a TREE_LIST because that function knew how to deal with pack expansions, and tsubst didn't. But tsubst_copy_and_build expects to be dealing with expressions, so we crash when trying to convert_from_reference a type. * pt.c (tsubst) [TREE_LIST]: Handle pack expansion. (tsubst_copy_and_build) [TRAIT_EXPR]: Always use tsubst for type2.