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From: "ed at catmur dot uk" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/109640] New: Spurious Wdangling-reference for argument to
 temporary lambda cast to rvalue reference
Date: Wed, 26 Apr 2023 23:24:05 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 13.1.0
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X-Bugzilla-Severity: normal
X-Bugzilla-Who: ed at catmur dot uk
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109640

            Bug ID: 109640
           Summary: Spurious Wdangling-reference for argument to temporary
                    lambda cast to rvalue reference
           Product: gcc
           Version: 13.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ed at catmur dot uk
  Target Milestone: ---

bool b() {
    int a;
    int&& i =3D [](int& r) -> int&& { return static_cast<int&&>(r); }(a);
    auto const l =3D [](int& r) -> int&& { return static_cast<int&&>(r); };
    int&& j =3D l(a);
    return &i =3D=3D &j;
}

<source>: In function 'bool b()':
<source>:3:11: warning: possibly dangling reference to a temporary
[-Wdangling-reference]
    3 |     int&& i =3D [](int& r) -> int&& { return static_cast<int&&>(r);=
 }(a);
      |           ^
<source>:3:68: note: the temporary was destroyed at the end of the full
expression '<lambda closure
object>b()::<lambda(int&)>().b()::<lambda(int&)>(a)'
    3 |     int&& i =3D [](int& r) -> int&& { return static_cast<int&&>(r);=
 }(a);
      |               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~=
^~~

The heuristic appears to be confused by the lambda itself being a temporary,
even though it is captureless.=