https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83417
Jason Merrill <jason at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |jason at gcc dot gnu.org --- Comment #6 from Jason Merrill <jason at gcc dot gnu.org> --- The issue seems to be that do_auto_deduction doesn't pass the previously deduced argument for T down to type_unification_real, so deduction fails.