https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93140
--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-9 branch has been updated by Jason Merrill <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:1a8996b0a7b238180f4a10b19b1e90b33e5b2df0 commit r9-8291-g1a8996b0a7b238180f4a10b19b1e90b33e5b2df0 Author: Jason Merrill <ja...@redhat.com> Date: Wed Feb 26 13:03:23 2020 -0500 c++: Fix decltype of empty pack expansion of parm. In unevaluated context, we only substitute a single PARM_DECL, not the entire chain, but the handling of an empty pack expansion was missing that check. gcc/cp/ChangeLog 2020-02-26 Jason Merrill <ja...@redhat.com> PR c++/93140 * pt.c (tsubst_decl) [PARM_DECL]: Check cp_unevaluated_operand in handling of TREE_CHAIN for empty pack.