https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101181
--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:2c699fd29829cd6115f78238dab7cab74f0a5009 commit r12-2222-g2c699fd29829cd6115f78238dab7cab74f0a5009 Author: Patrick Palka <ppa...@redhat.com> Date: Fri Jul 9 10:20:25 2021 -0400 c++: requires-expr with dependent extra args [PR101181] Here we're crashing ultimately because the mechanism for delaying substitution into a requires-expression (and constexpr if and pack expansions) doesn't expect to see dependent args. But we end up capturing dependent args here during substitution into the default template argument as part of coerce_template_parms for the dependent specialization p<T>. This patch enables the commented out code in add_extra_args for handling this situation. This isn't needed for pack expansions (as the accompanying comment points out), and it doesn't seem strictly necessary for constexpr if either, but for requires-expressions delaying even dependent substitution is important for ensuring we don't evaluate requirements out of order. It turns out we also need to make a copy of the arguments when capturing them so that coerce_template_parms doesn't later add to them and form an unexpected cycle (REQUIRES_EXPR_EXTRA_ARGS (t) would indirectly point to t). We also need to make tsubst_template_args handle missing template arguments, since the arguments we capture from coerce_template_parms and are incomplete at that point. PR c++/101181 gcc/cp/ChangeLog: * constraint.cc (tsubst_requires_expr): Pass complain/in_decl to add_extra_args. * cp-tree.h (add_extra_args): Add complain/in_decl parameters. * pt.c (build_extra_args): Make a copy of args. (add_extra_args): Add complain/in_decl parameters. Enable the code for handling the case where the extra arguments are dependent. (tsubst_pack_expansion): Pass complain/in_decl to add_extra_args. (tsubst_template_args): Handle missing template arguments. (tsubst_expr) <case IF_STMT>: Pass complain/in_decl to add_extra_args. gcc/testsuite/ChangeLog: * g++.dg/cpp2a/concepts-requires26.C: New test. * g++.dg/cpp2a/lambda-uneval16.C: New test.
