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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104492

            Bug ID: 104492
           Summary: Bogus dangling pointer warning (dangling pointer to
                    =E2=80=98candidates=E2=80=99 may be used [-Werror=3Ddan=
gling-pointer=3D])
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: thiago at kde dot org
  Target Milestone: ---

Created attachment 52409
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D52409&action=3Dedit
Preprocessed sources for qlibrary.cpp

Workaround: https://codereview.qt-project.org/c/qt/qtbase/+/394894
Original sources:=20
https://code.qt.io/cgit/qt/qtbase.git/tree/src/corelib/plugin/qlibrary.cpp?=
id=3D5e378aaff61c9708e0657f3ee29517c06cb075fa#n618
https://github.com/qt/qtbase/blob/5e378aaff61c9708e0657f3ee29517c06cb075fa/=
src/corelib/plugin/qlibrary.cpp#L618-L677

Code snippet:

    auto isValidSuffix =3D [](QStringView s) {
        const QLatin1String candidates[] =3D {
            QLatin1String("so"),
        };
        return std::find(std::begin(candidates), std::end(candidates), s) !=
=3D
std::end(candidates);
    };
    auto suffixes =3D qTokenize(completeSuffix, u'.');
    auto it =3D suffixes.begin();
    const auto end =3D suffixes.end();
    while (it !=3D end) {
        if (isValidSuffix(*it++))
          return true;
    }
    return false;

This code above produces the warning:
qlibrary.cpp:114:9: error: dangling pointer to =E2=80=98candidates=E2=80=99=
 may be used
[-Werror=3Ddangling-pointer=3D]=20=20=20=20=20=20=20=20=20=20
  114 |         if (isValidSuffix(*it++))=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20
      |         ^~=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
qlibrary.cpp:76:29: note: =E2=80=98candidates=E2=80=99 declared here=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20
   76 |         const QLatin1String candidates[] =3D {=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
      |                             ^~~~~~~~~~=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20

The 'candidates' variable has indeed gone out of scope, but there's no use =
of
its pointer where the lambda is used. The lambda does a std::find, which
returns a pointer into the array, but that pointer is compared to std::end =
and
the lambda returns a boolean.

Compile the attached preprocessed sources with:
 g++ -march=3Dx86-64-v3 -Wall -Wextra -O3 -o /dev/null -c qlibrary.cpp.ii

GCC commit 1ce5395977f37e8d0c03394f7b932a584ce85cc7 (master branch dated
2022-02-09).=