[Bug c++/110025] New: ICE with default-argument for template-param with decltype and auto.

[Bug c++/110025] New: ICE with default-argument for template-param with decltype and auto.

[jehelset at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110025

            Bug ID: 110025
           Summary: ICE with default-argument for template-param with
                    decltype and auto.
           Product: gcc
           Version: 13.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jehelset at gmail dot com
  Target Milestone: ---

Compiler ICE when using
decltype(auto(variable-template<earlier-template-param>)) as default-argument
of a template-param:

https://godbolt.org/z/M9qrvTj8P

[Bug c++/110025] ICE with default-argument for template-param with decltype and auto.

[jehelset at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110025

--- Comment #1 from John Eivind Helset <jehelset at gmail dot com> ---
Some other weirdness related to use of `auto(expr)` in template-arguments:

https://godbolt.org/z/jf64xExTW

Might be a separate bug.

[Bug c++/110025] ICE with default-argument for template-param with decltype and auto.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110025

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Created attachment 55200
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55200&action=edit
testcase 1

Please next time attach the testcases rather than just links to godbolt.

[Bug c++/110025] ICE with default-argument for template-param with decltype and auto.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110025

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Created attachment 55201
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55201&action=edit
testcase 2

[Bug c++/110025] ICE with default-argument for template-param with decltype and auto.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110025

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Created attachment 55202
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55202&action=edit
self contained testcase for testcase 2

No headers.  -std=c++2b

[Bug c++/110025] [C++23] ICE with default-argument for template-param with decltype and auto.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110025

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Created attachment 55203
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55203&action=edit
reduced self-contained testcase for testcase #1

This removes all of the unneeded code really.

[Bug c++/110025] [C++23] ICE with default-argument for template-param with decltype and auto.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110025

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
           Keywords|                            |ice-on-valid-code,
                   |                            |rejects-valid
   Last reconfirmed|                            |2023-05-30

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.

[Bug c++/110025] [C++23] ICE with default-argument for template-param with decltype and auto.

[jehelset at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110025

--- Comment #7 from John Eivind Helset <jehelset at gmail dot com> ---
(In reply to Andrew Pinski from comment #2)
> Created attachment 55200 [details]
> testcase 1
> 
> Please next time attach the testcases rather than just links to godbolt.

Will do! Thanks.

[Bug c++/110025] [C++23] ICE with default-argument for template-param with decltype and auto.

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110025

--- Comment #8 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:a6a1920b592b58c38137c5c891b3bbb02b084f38

commit r14-9260-ga6a1920b592b58c38137c5c891b3bbb02b084f38
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri Mar 1 12:50:18 2024 -0500

    c++: auto(x) partial substitution [PR110025, PR114138]

    In r12-6773-g09845ad7569bac we gave CTAD placeholders a level of 0 and
    ensured we never replaced them via tsubst.  It turns out that autos
    representing an explicit cast need the same treatment and for the same
    reason: such autos appear in an expression context and so their level
    gets easily messed up after partial substitution, leading to premature
    replacement via an incidental tsubst instead of via do_auto_deduction.

    This patch fixes this by extending the r12-6773 approach to auto(x).

            PR c++/110025
            PR c++/114138

    gcc/cp/ChangeLog:

            * cp-tree.h (make_cast_auto): Declare.
            * parser.cc (cp_parser_functional_cast): If the type is an auto,
            replace it with a level-less one via make_cast_auto.
            * pt.cc (find_parameter_packs_r): Don't treat level-less auto
            as a type parameter pack.
            (tsubst) <case TEMPLATE_TYPE_PARM>: Generalize CTAD placeholder
            auto handling to all level-less autos.
            (make_cast_auto): Define.
            (do_auto_deduction): Handle replacement of a level-less auto.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp23/auto-fncast16.C: New test.
            * g++.dg/cpp23/auto-fncast17.C: New test.
            * g++.dg/cpp23/auto-fncast18.C: New test.

    Reviewed-by: Jason Merrill <jason@redhat.com>