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Subject: [Bug c++/89741] [9 Regression] static_assert fires when template not
 instantiated
Date: Sat, 18 Feb 2023 21:19:23 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D89741

--- Comment #12 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:9944ca17c0766623bce260684edc614def7ea761

commit r13-6133-g9944ca17c0766623bce260684edc614def7ea761
Author: Jason Merrill <jason@redhat.com>
Date:   Fri Feb 10 16:16:45 2023 -0800

    c++: static_assert (false) in template [DR2518]

    For a long time, people have expected to be able to write
    static_assert (false) in a template and only have it diagnosed if the
    template is instantiated, but we (and other implementations) gave an er=
ror
    about the uninstantiated template because the standard says that if no
valid
    instantiation of the template is possible, the program is ill-formed, no
    diagnostic required, and we try to diagnose IFNDR things when feasible.

    At the meeting last week we were looking at CWG2518, which wanted to
specify
    that an implementation must not accept a program containing a failing
#error
    or static_assert.  We also looked at P2593, which proposed allowing
    static_assert in an uninstantiated template.  We ended up combining the=
se
    two in order to avoid requiring implementations to reject programs with
    static_assert (false) in uninstantiated templates.

    The committee accepted this as a DR, so I'm making the change to all
    standard modes.  This behavior was also conformant previously, since no
    diagnostic was required in this case.

    We continue to diagnose non-constant or otherwise ill-formed conditions=
, so
    no changes to existing tests were needed.

            DR 2518
            PR c++/52809
            PR c++/53638
            PR c++/87389
            PR c++/89741
            PR c++/92099
            PR c++/104041
            PR c++/104691

    gcc/cp/ChangeLog:

            * semantics.cc (finish_static_assert): Don't diagnose in
            template context.

    gcc/testsuite/ChangeLog:

            * g++.dg/DRs/dr2518.C: New test.=