https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92103
--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-10 branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:a3a71447513cd6aee06631e1cc73a530e2c7fd95 commit r10-8228-ga3a71447513cd6aee06631e1cc73a530e2c7fd95 Author: Patrick Palka <ppa...@redhat.com> Date: Thu Jun 4 13:03:58 2020 -0400 c++: constrained nested partial specialization [PR92103] When determining the most specialized partial specialization of a primary template that is nested inside a class template, we first tsubst the outer template arguments into the TEMPLATE_DECL of each partial specialization, and then check for satisfaction of each of the new TEMPLATE_DECL's constraints. But tsubst_template_decl does not currently guarantee that constraints from the original DECL_TEMPLATE_RESULT get reattached to the new DECL_TEMPLATE_RESULT. In the testcase below, this leads to the constraints_satisfied_p check in most_specialized_partial_spec to trivially return true for each of the partial specializations. I'm not sure if such a guarantee would be desirable, but in this case we can just check constraints_satisfied_p on the original TEMPLATE_DECL instead of on the tsubsted TEMPLATE_DECL here, which is what this patch does (alongside some reorganizing). gcc/cp/ChangeLog: PR c++/92103 * pt.c (most_specialized_partial_spec): Reorganize the loop over DECL_TEMPLATE_SPECIALIZATIONS. Check constraints_satisfied_p on the original template declaration, not on the tsubsted one. gcc/testsuite/ChangeLog: PR c++/92103 * g++.dg/cpp2a/concepts-partial-spec7.C: New test. (cherry picked from commit aee69073cdb8086d393f12474c6177e75467ceaa)
