[Bug c++/111493] New: [concepts] multidimensional subscript operator inside requires is broken

[Bug c++/111493] New: [concepts] multidimensional subscript operator inside requires is broken

[elrodc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111493

            Bug ID: 111493
           Summary: [concepts] multidimensional subscript operator inside
                    requires is broken
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: elrodc at gmail dot com
  Target Milestone: ---

Two example programs:

>  #include <concepts>
>  constexpr auto foo(const auto &A, int i, int j)  requires(requires(decltype(A) a, int ii) { a[ii, ii]; }) {
>    return A[i, j];
>  }
>  constexpr auto foo(const auto &A, int i, int j) {
>    return A + i + j;
>  }
>  static_assert(foo(2,3,4) == 9);


>  #include <concepts>
>  template <typename T, typename S>
>  concept CartesianIndexable = requires(T t, int i) {
>    { t[i, i] } -> std::convertible_to<S>;
>  };
>  static_assert(!CartesianIndexable<double,int>);

These result in errors of the form

  error: invalid types 'const int[int]' for array subscript

Here is godbolt for reference: https://godbolt.org/z/WE66nY8zG

The invalid subscript should result in the `requires` failing, not an error.

[Bug c++/111493] [concepts] multidimensional subscript operator inside requires is broken

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111493

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
                 CC|                            |ppalka at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2023-09-20

--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Confirmed.

[Bug c++/111493] [concepts] multidimensional subscript operator inside requires is broken

[elrodc at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111493

--- Comment #2 from Chris Elrod <elrodc at gmail dot com> ---
Note that it also shows up in gcc-13. I put gcc-14 as the version to indicate
that I confirmed it is still a problem on latest trunk. Not sure what the
policy is on which version we should report.

[Bug c++/111493] [concepts] multidimensional subscript operator inside requires is broken

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111493

--- Comment #3 from CVS 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:1fea14def849dd38b098b0e2d54e64801f9c1f43

commit r14-4225-g1fea14def849dd38b098b0e2d54e64801f9c1f43
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri Sep 22 06:27:48 2023 -0400

    c++: missing SFINAE in grok_array_decl [PR111493]

    We should guard both the diagnostic and backward compatibilty fallback
    code with tf_error, so that in a SFINAE context we don't issue any
    diagnostics and correctly treat ill-formed C++23 multidimensional
    subscript operator expressions as such.

            PR c++/111493

    gcc/cp/ChangeLog:

            * decl2.cc (grok_array_decl): Guard diagnostic and backward
            compatibility fallback code paths with tf_error.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp23/subscript15.C: New test.

[Bug c++/111493] [concepts] multidimensional subscript operator inside requires is broken

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111493

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-13 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:40d2dec34b58c3c31b1c731049a914204ec252c3

commit r13-7837-g40d2dec34b58c3c31b1c731049a914204ec252c3
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri Sep 22 06:27:48 2023 -0400

    c++: missing SFINAE in grok_array_decl [PR111493]

    We should guard both the diagnostic and backward compatibilty fallback
    code with tf_error, so that in a SFINAE context we don't issue any
    diagnostics and correctly treat ill-formed C++23 multidimensional
    subscript operator expressions as such.

            PR c++/111493

    gcc/cp/ChangeLog:

            * decl2.cc (grok_array_decl): Guard diagnostic and backward
            compatibility fallback code paths with tf_error.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp23/subscript15.C: New test.

    (cherry picked from commit 1fea14def849dd38b098b0e2d54e64801f9c1f43)

[Bug c++/111493] [concepts] multidimensional subscript operator inside requires is broken

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111493

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |13.3
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #5 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 13.3 / 14, thanks for the bug report.

[Bug c++/111493] [concepts] multidimensional subscript operator inside requires is broken

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111493

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ldalessandro at gmail dot com

--- Comment #6 from Patrick Palka <ppalka at gcc dot gnu.org> ---
*** Bug 108736 has been marked as a duplicate of this bug. ***