[Bug c++/112436] New: SFINAE-unfriendly error on throwing pointer to incomplete type

[Bug c++/112436] New: SFINAE-unfriendly error on throwing pointer to incomplete type

[arthur.j.odwyer at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112436

            Bug ID: 112436
           Summary: SFINAE-unfriendly error on throwing pointer to
                    incomplete type
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: arthur.j.odwyer at gmail dot com
  Target Milestone: ---

====
template<class T>
concept Throwable = requires { throw T(); };
struct Incomplete;

static_assert(!Throwable<Incomplete*>);
static_assert(!Throwable<int(*)[]>);
====

<source>:2:32: error: invalid use of incomplete type 'struct Incomplete'
    2 | concept Throwable = requires { throw T(); };
      |                                ^~~~~~~~~
<source>:3:8: note: forward declaration of 'struct Incomplete'
    3 | struct Incomplete;
      |        ^~~~~~~~~~
<source>:2:32: error: invalid use of array with unspecified bounds
    2 | concept Throwable = requires { throw T(); };
      |                                ^~~~~~~~~

Instead of a hard error in both cases, we expect the concept to be false and
the static_assert to succeed. Clang and EDG succeed. MSVC succeeds on
`Incomplete*` and incorrectly permits throwing `int(*)[]`.

The terse/multi-purpose "invalid use of..." error message seems to come up a
lot in Bugzilla, but I didn't see any search hits for that message plus the
word "throw".

Bug #98388 is probably related.

[Bug c++/112436] SFINAE-unfriendly error on throwing pointer to incomplete type

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112436

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=112437
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2023-11-08
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.

While looking into this to see if a slightly different testcase would work, I
found PR 112437 which ICEs.

Note there needs to be a complete type; using an incomplete type causes the
error message like here.

[Bug c++/112436] SFINAE-unfriendly error on throwing pointer to incomplete type

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112436

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|                            |mpolacek at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |mpolacek at gcc dot gnu.org

[Bug c++/112436] SFINAE-unfriendly error on throwing pointer to incomplete type

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112436

--- Comment #2 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:ecc119effe1aa445cb973c8cbb5ef3830f256f13

commit r14-8958-gecc119effe1aa445cb973c8cbb5ef3830f256f13
Author: Marek Polacek <polacek@redhat.com>
Date:   Sat Feb 10 10:52:18 2024 -0500

    c++: SFINAE-unfriendly error on throwing pointer [PR112436]

    On the heels of r14-8903, this patch adds further complain parameters
    so that we don't emit "invalid use of incomplete type" from inside
    a concept.

            PR c++/112436

    gcc/cp/ChangeLog:

            * except.cc (expand_start_catch_block): Pass tf_warning_or_error to
            is_admissible_throw_operand_or_catch_parameter.
            (build_throw): Pass complain to
            is_admissible_throw_operand_or_catch_parameter.
            (complete_ptr_ref_or_void_ptr_p): Add a tsubst_flags_t parameter. 
Use
            it.  Return bool.  Call complete_type_or_maybe_complain instead of
            complete_type_or_else.
            (is_admissible_throw_operand_or_catch_parameter): Add a
tsubst_flags_t
            parameter.  Use it.  Guard error calls.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp2a/concepts-pr112436.C: New test.

[Bug c++/112436] SFINAE-unfriendly error on throwing pointer to incomplete type

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112436

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Fixed for GCC 14.