https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102412
--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-11 branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:5a411459b73b65d8a1235a16d6e2aac4eed17338 commit r11-9082-g5a411459b73b65d8a1235a16d6e2aac4eed17338 Author: Patrick Palka <ppa...@redhat.com> Date: Wed Sep 22 11:16:53 2021 -0400 c++: concept-ids and value-dependence [PR102412] The problem here is that uses_template_parms returns true for all concept-ids (even those with non-dependent arguments), so when a concept-id is used as a default template argument then during deduction the default argument is considered dependent even after substituting into it, which leads to deduction failure (from type_unification_real). This patch fixes this by implementing the resolution of CWG 2446 which says a concept-id is dependent only if its arguments are. DR 2446 PR c++/102412 gcc/cp/ChangeLog: * constexpr.c (cxx_eval_constant_expression) <case TEMPLATE_ID_EXPR>: Check value_dependent_expression_p instead of processing_template_decl. * pt.c (value_dependent_expression_p) <case TEMPLATE_ID_EXPR>: Return true only if any_dependent_template_arguments_p. (instantiation_dependent_r) <case CALL_EXPR>: Remove this case. <case TEMPLATE_ID_EXPR>: Likewise. gcc/testsuite/ChangeLog: * g++.dg/cpp2a/concepts-nondep2.C: New test. * g++.dg/cpp2a/concepts-nondep3.C: New test. (cherry picked from commit 9329344a6d81a6a5e3bd171167ebc7b158bb44f4)
