[Bug libstdc++/118160] Dangling reference in std::ranges::is_permutation may cause a crash

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118160

--- Comment #2 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:

https://gcc.gnu.org/g:2a2bd96d0d2109384a0eedde843ba811d2e18738

commit r15-7424-g2a2bd96d0d2109384a0eedde843ba811d2e18738
Author: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Date:   Thu Feb 6 14:24:17 2025 +0000

    libstdc++: fix a dangling reference crash in ranges::is_permutation
[PR118160]

    The code was caching the result of `invoke(proj, *it)` in a local
    `auto &&` variable. The problem is that this may create dangling
    references, for instance in case `proj` is `std::identity` (the common
    case) and `*it` produces a prvalue: lifetime extension does not
    apply here due to the expressions involved.

    Instead, store (and lifetime-extend) the result of `*it` in a separate
    variable, then project that variable. While at it, also forward the
    result of the projection to the predicate, so that the predicate can
    act on the proper value category.

    libstdc++-v3/ChangeLog:

            PR libstdc++/118160
            PR libstdc++/100249
            * include/bits/ranges_algo.h (__is_permutation_fn): Avoid a
            dangling reference by storing the result of the iterator
            dereference and the result of the projection in two distinct
            variables, in order to lifetime-extend each one.
            Forward the projected value to the predicate.
            * testsuite/25_algorithms/is_permutation/constrained.cc: Add a
            test with a range returning prvalues. Test it in a constexpr
            context, in order to rely on the compiler to catch UB.

    Signed-off-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>