https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99811
Bug ID: 99811 Summary: ICE: tree check: accessed elt 2 of 'tree_vec' with 1 elts in tsubst_pack_expansion, at cp/pt.c:13002 Product: gcc Version: 11.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: hewillk at gmail dot com Target Milestone: --- https://godbolt.org/z/shj7Tr65M related to PR 99809: #include <concepts> template <typename... Ts> auto f(Ts...) { return []<typename... Us>(std::same_as<Ts> auto...) {}; } int main() { f(0, 0.5)(); } <source>:9:12: internal compiler error: tree check: accessed elt 2 of 'tree_vec' with 1 elts in tsubst_pack_expansion, at cp/pt.c:13002 9 | f(0, 0.5)(); | ~~~~~~~~~^~ 0x1cfb7f9 internal_error(char const*, ...) ???:0 0x67bcb2 tree_vec_elt_check_failed(int, int, char const*, int, char const*) ???:0 0x93095c tsubst_pack_expansion(tree_node*, tree_node*, int, tree_node*) ???:0 0x73efca constraints_satisfied_p(tree_node*, tree_node*) ???:0 0x954963 fn_type_unification(tree_node*, tree_node*, tree_node*, tree_node* const*, unsigned int, tree_node*, unification_kind_t, int, conversion**, bool, bool) ???:0 0x6e225e build_op_call(tree_node*, vec<tree_node*, va_gc, vl_embed>**, int) ???:0 0x980ae5 finish_call_expr(tree_node*, vec<tree_node*, va_gc, vl_embed>**, bool, bool, int) ???:0 0x8e12ad c_parse_file() ???:0 0xa600a2 c_common_parse_file() ???:0 Please submit a full bug report, with preprocessed source if appropriate. Please include the complete backtrace with any bug report.