https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68372
--- Comment #1 from lucdanton at free dot fr --- On 7 trunk (rev. 239680) it looks like the program now triggers an ICE: $ g++-trunk -std=c++1z -fconcepts main.cpp main.cpp: In substitution of 'template<class ... X> requires C<X>... void foo::bar(X ...) [with X = {}]': main.cpp:18:16: required from here main.cpp:11:10: internal compiler error: in tsubst_constraint, at cp/constraint.cc:1957 void bar(X...) ^~~ 0x764263 tsubst_constraint(tree_node*, tree_node*, int, tree_node*) ../../gcc/gcc/cp/constraint.cc:1957 0x764362 tsubst_constraint_info(tree_node*, tree_node*, int, tree_node*) ../../gcc/gcc/cp/constraint.cc:1919 0x661f65 tsubst_decl ../../gcc/gcc/cp/pt.c:11967 0x667834 tsubst(tree_node*, tree_node*, int, tree_node*) ../../gcc/gcc/cp/pt.c:12907 0x670290 instantiate_template_1 ../../gcc/gcc/cp/pt.c:17558 0x670290 instantiate_template(tree_node*, tree_node*, int) ../../gcc/gcc/cp/pt.c:17609 0x67701a fn_type_unification(tree_node*, tree_node*, tree_node*, tree_node* const*, unsigned int, tree_node*, unification_kind_t, int, bool, bool) ../../gcc/gcc/cp/pt.c:17984 0x62a048 add_template_candidate_real ../../gcc/gcc/cp/call.c:3119 0x62a813 add_template_candidate ../../gcc/gcc/cp/call.c:3197 0x62a813 add_candidates ../../gcc/gcc/cp/call.c:5384 0x62afe5 build_new_method_call_1 ../../gcc/gcc/cp/call.c:8421 0x62afe5 build_new_method_call(tree_node*, tree_node*, vec<tree_node*, va_gc, vl_embed>**, tree_node*, int, tree_node**, int) ../../gcc/gcc/cp/call.c:8620 0x6bb668 cp_parser_postfix_expression ../../gcc/gcc/cp/parser.c:6908 0x6b9832 cp_parser_unary_expression ../../gcc/gcc/cp/parser.c:8019 0x6c1787 cp_parser_cast_expression ../../gcc/gcc/cp/parser.c:8696 0x6c1d53 cp_parser_binary_expression ../../gcc/gcc/cp/parser.c:8797 0x6c2434 cp_parser_assignment_expression ../../gcc/gcc/cp/parser.c:9084 0x6c48aa cp_parser_expression ../../gcc/gcc/cp/parser.c:9253 0x6c4e8f cp_parser_expression_statement ../../gcc/gcc/cp/parser.c:10736 0x6d17d4 cp_parser_statement ../../gcc/gcc/cp/parser.c:10587