[Bug libstdc++/100187] Helper lambda in ranges_algo.h misses forwarding return type

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100187

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:139bafaaba0c775ca65712621bd60e079b488d73

commit r10-10210-g139bafaaba0c775ca65712621bd60e079b488d73
Author: Patrick Palka <ppalka@redhat.com>
Date:   Tue Apr 27 23:21:19 2021 -0400

    libstdc++: Fix various bugs in ranges_algo.h [PR100187, ...]

    This fixes some bugs with our ranges algorithms in uncommon situations,
    such as when the return type of a predicate is a non-copyable class type
    that's implicitly convertible to bool (PR100187), when a comparison
    predicate isn't invocable as an rvalue (PR100237), and when the return
    type of a projection function is non-copyable (PR100249).

    This also fixes PR100287, which reports that we're moving __first twice
    when constructing with it an empty subrange in ranges::partition.

    libstdc++-v3/ChangeLog:

            PR libstdc++/100187
            PR libstdc++/100237
            PR libstdc++/100249
            PR libstdc++/100287
            * include/bits/ranges_algo.h (__search_n_fn::operator()): Give
            the __value_comp lambda an explicit bool return type.
            (__is_permutation_fn::operator()): Give the __proj_scan local
            variable auto&& return type.  Give the __comp_scan lambda an
            explicit bool return type.
            (__remove_fn::operator()): Give the __pred lambda an explicit
            bool return type.
            (__partition_fn::operator()): Don't std::move __first twice
            when returning an empty subrange.
            (__min_fn::operator()): Don't std::move __comp.
            (__max_fn::operator()): Likewise.
            (__minmax_fn::operator()): Likewise.

    (cherry picked from commit d91e7eab3a2c3957c2220ad71e62d9fc78cccb9b)