[Bug c++/105497] New: -Wswitch ignores [[maybe_unused]] for an enumerator

[Bug c++/105497] New: -Wswitch ignores [[maybe_unused]] for an enumerator

[olafurw at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105497

            Bug ID: 105497
           Summary: -Wswitch ignores [[maybe_unused]] for an enumerator
           Product: gcc
           Version: 11.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: olafurw at gmail dot com
  Target Milestone: ---

enum class Button
{
    Left,
    Right,
    Middle,
    NumberOfButtons [[maybe_unused]]
};

int main()
{
    Button b = Button::Left;
    switch (b) {
        case Button::Left:
        case Button::Right:
        case Button::Middle:
            break;
//#ifdef __GNUC__
//        case Button::NumberOfButtons:
//            __builtin_unreachable();
//#endif
    }
}

https://godbolt.org/z/d5M5MYc45

No warning generated for Clang or MSVC but it does for GCC. Works with
__builtin_unreachable()

LLVM bug report about the same thing:
https://bugs.llvm.org/show_bug.cgi?id=36231

[Bug c++/105497] -Wswitch ignores [[maybe_unused]] for an enumerator

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105497

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2022-05-05
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
           Keywords|                            |diagnostic
                 CC|                            |mpolacek at gcc dot gnu.org

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Ah, that's interesting.  Confirmed.

[Bug c++/105497] -Wswitch ignores [[maybe_unused]] for an enumerator

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105497

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

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

[Bug c++/105497] -Wswitch ignores [[maybe_unused]] for an enumerator

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105497

--- Comment #2 from CVS 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:60fdce11dc9e5ddf671b07a3fc6ed70476860b22

commit r13-622-g60fdce11dc9e5ddf671b07a3fc6ed70476860b22
Author: Marek Polacek <polacek@redhat.com>
Date:   Sat May 7 16:15:49 2022 -0400

    c, c++: -Wswitch warning on [[maybe_unused]] enumerator [PR105497]

    This PR complains that we emit the "enumeration value not handled in
    switch" warning even though the enumerator was marked with the
    [[maybe_unused]] attribute.

    I couldn't just check TREE_USED, because the enumerator could have been
    used earlier in the function, which doesn't play well with the
    c_do_switch_warnings warning.  Instead, I had to check the attributes on
    the CONST_DECL.  This is easy since the TYPE_VALUES of an enum type are
    now consistent between C and C++, both of which store the CONST_DECL in
    its TREE_VALUE.

            PR c++/105497

    gcc/c-family/ChangeLog:

            * c-warn.cc (c_do_switch_warnings): Don't warn about unhandled
            enumerator when it was marked with attribute unused.

    gcc/testsuite/ChangeLog:

            * c-c++-common/Wswitch-1.c: New test.
            * g++.dg/warn/Wswitch-4.C: New test.

[Bug c++/105497] -Wswitch ignores [[maybe_unused]] for an enumerator

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105497

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

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

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Fixed for GCC 13.