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From: "tilkax at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/96311] New: false positive for -Wunused-but-set-variable
 (const/constexpr identifier used in generic lambda)
Date: Fri, 24 Jul 2020 15:36:42 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96311

            Bug ID: 96311
           Summary: false positive for -Wunused-but-set-variable
                    (const/constexpr identifier used in generic lambda)
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tilkax at gmail dot com
  Target Milestone: ---

Using gcc version 11.0.0 20200723, this code:

void foo()
{
    constexpr int used =3D 0;
    [](auto unused)
    {
        return used;
    };
}

triggers an incorrect warning:

<source>:3:19: warning: variable 'used' set but not used
[-Wunused-but-set-variable]
    3 |     constexpr int used =3D 0;
      |                   ^~~~

It doesn't matter whether the lambda is called but it does need to be a gen=
eric
lambda to trigger the incorrect warning.

Also, both the lambda parameter as well as the lambda itself are unused here
but don't trigger any warnings :/=