https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99008
--- 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:8913b2c2bcded39427ff27e6dfc276ae8555f6b8 commit r11-8155-g8913b2c2bcded39427ff27e6dfc276ae8555f6b8 Author: Patrick Palka <ppa...@redhat.com> Date: Tue Apr 13 12:35:33 2021 -0400 c++: Reject alias CTAD in C++17 [PR99008] Here, in C++17 mode, we only pedwarn about the use of alias CTAD and then later ICE from alias_ctad_tweaks when attempting to constrain the guides. Since the construction of the guides of an alias template effectively relies on concepts, we shouldn't be permissive about alias CTAD in C++17 mode, so this patch turns the pertinent pedwarn in do_class_deduction into an error. In order to get a consistent diagnostic for B() vs the other forms in the added testcase, I had to remove the special handling of CTAD with empty initializer in build_functional_cast_1 so that we always pass 'complain' to do_auto_deduction. gcc/cp/ChangeLog: PR c++/99008 * pt.c (do_class_deduction): Reject alias CTAD in C++17 mode rather than issuing a pedwarn. * typeck2.c (build_functional_cast_1): Handle CTAD uniformly for consistent diagnostics. gcc/testsuite/ChangeLog: PR c++/99008 * g++.dg/parse/template2.C: Adjust expected diagnostic. * g++.dg/template/error8.C: Likewise. * g++.dg/cpp1z/class-deduction84.C: New test.
