[Bug c++/113256] New: False -Wdangling-reference positive

[Bug c++/113256] New: False -Wdangling-reference positive

[pdimov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113256

            Bug ID: 113256
           Summary: False -Wdangling-reference positive
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pdimov at gmail dot com
  Target Milestone: ---

The following code
```
#include <utility>
#include <cassert>

template<class M, class T, class A> auto bind( M T::* pm, A a )
{
    return [=]( auto&& x ) -> M const& { return x.*pm; };
}

template<int I> struct arg {};

arg<1> _1;

int main()
{
    std::pair<int, int> pair;
    int const& x = bind( &std::pair<int, int>::first, _1 )( pair );
    assert( &x == &pair.first );
}
```
(https://godbolt.org/z/a555MMTqo)

(reduced from a Boost.Bind test case)

causes

```
<source>:16:16: warning: possibly dangling reference to a temporary
[-Wdangling-reference]
   16 |     int const& x = bind( &std::pair<int, int>::first, _1 )( pair );
      |                ^
```

with GCC 13.2 (but not trunk).

There are indeed two temporaries created in that full expression, but `int
const&` can't possibly bind to any of them.

[Bug c++/113256] False -Wdangling-reference positive

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113256

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2024-01-18
     Ever confirmed|0                           |1

[Bug c++/113256] False -Wdangling-reference positive

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113256

--- Comment #1 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:9010fdba68063beccfbab0aa9ec8739f232ca2f4

commit r14-8375-g9010fdba68063beccfbab0aa9ec8739f232ca2f4
Author: Marek Polacek <polacek@redhat.com>
Date:   Fri Jan 19 13:59:41 2024 -0500

    c++: -Wdangling-reference and lambda false warning [PR109640]

    -Wdangling-reference checks if a function receives a temporary as its
    argument, and only warns if any of the arguments was a temporary.  But
    we should not warn when the temporary represents a lambda or we generate
    false positives as in the attached testcases.

            PR c++/113256
            PR c++/111607
            PR c++/109640

    gcc/cp/ChangeLog:

            * call.cc (do_warn_dangling_reference): Don't warn if the temporary
            is of lambda type.

    gcc/testsuite/ChangeLog:

            * g++.dg/warn/Wdangling-reference14.C: New test.
            * g++.dg/warn/Wdangling-reference15.C: New test.
            * g++.dg/warn/Wdangling-reference16.C: New test.

[Bug c++/113256] False -Wdangling-reference positive

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113256

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

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

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Should be fixed; thanks for the report.