https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107390
--- Comment #2 from GCC 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:82c2acd0bc4411524a8248fcdce219927d921a71 commit r15-3694-g82c2acd0bc4411524a8248fcdce219927d921a71 Author: Patrick Palka <ppa...@redhat.com> Date: Wed Sep 18 13:50:43 2024 -0400 c++: alias of decltype(lambda) is opaque [PR116714, PR107390] Here for using type = decltype([]{}); static_assert(is_same_v<type, type>); we strip the alias ahead of time during template argument coercion which effectively transforms the template-id into is_same_v<decltype([]{}), decltype([]{})> which is wrong because later substitution into the template-id will produce two new lambdas with distinct types and cause is_same_v to return false. This demonstrates that such aliases should be considered opaque (a notion that we recently introduced in r15-2331-g523836716137d0). (An alternative solution might be to consider memoizing lambda-expr substitution rather than always producing a new lambda, but this is much simpler.) PR c++/116714 PR c++/107390 gcc/cp/ChangeLog: * pt.cc (dependent_opaque_alias_p): Also return true for a decltype(lambda) alias. gcc/testsuite/ChangeLog: * g++.dg/cpp2a/lambda-uneval18.C: New test. Reviewed-by: Jason Merrill <ja...@redhat.com>
