https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101906
--- Comment #3 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:c3ba0eaaa223f7b8208d279e3f39ff134912f9e9 commit r13-2633-gc3ba0eaaa223f7b8208d279e3f39ff134912f9e9 Author: Patrick Palka <ppa...@redhat.com> Date: Tue Jun 7 14:19:53 2022 -0400 c++: template-id arguments are evaluated [PR101906] Here we're neglecting to clear cp_unevaluated_operand when substituting into the arguments of the alias template-id 'skip<(T(), 0), T>' with T=A, which means cp_unevaluated_operand remains set during mark_used for A::A() and so we don't synthesize it. Later constant evaluation for the substituted template argument '(A(), 0)' (from coerce_template_parms) fails with "'constexpr A::A()' used before its definition" since it was never synthesized. This doesn't happen with a class template because tsubst_aggr_type clears cp_unevaluated_operand during substitution thereof. But since template arguments are generally manifestly constant-evaluated, which in turn are evaluated even in an unevaluated operand, we should be clearing cp_unevaluated_operand more broadly whenever substituting into any set of template arguments. To that end this patch makes us clear it during tsubst_template_args. PR c++/101906 gcc/cp/ChangeLog: * pt.cc (tsubst_template_args): Set cp_evaluated here. (tsubst_aggr_type): Not here. gcc/testsuite/ChangeLog: * g++.dg/template/evaluated1.C: New test. * g++.dg/template/evaluated1a.C: New test. * g++.dg/template/evaluated1b.C: New test. * g++.dg/template/evaluated1c.C: New test.
