[Bug libstdc++/125981] std::find_if/std::mismatch dereference the past-the-end iterator when the predicate result type has an ADL-reachable operator&&

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125981

--- Comment #13 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-16 branch has been updated by Jonathan Wakely
<[email protected]>:

https://gcc.gnu.org/g:8618618b466b819d27930bdb6cf1b765099a2c22

commit r16-9548-g8618618b466b819d27930bdb6cf1b765099a2c22
Author: Yan Churkin <[email protected]>
Date:   Fri Jun 26 22:45:31 2026 +0300

    libstdc++: Don't dereference past-the-end iterator with overloaded
operator&& [PR125981]

    std::__find_if, std::__mismatch and std::__push_heap drove their loops
    with a condition of the form

      while (__first != __last && PREDICATE_CALL(...))

    If the predicate/comparator result type has an ADL-reachable
    operator&&(bool, T), overload resolution selects that user-defined
    operator&& for the loop condition.  It does not short-circuit, so the
    operand that dereferences *__first is evaluated even when
    __first == __last, dereferencing the past-the-end iterator.

    Such a result type does not model boolean-testable, so this is undefined
    behaviour and not a conformance issue.  Handle it anyway as a QoI
    extension, consistent with std::equal, std::binary_search and
    std::__partition, by forcing the predicate result to bool so the
    built-in && is used.  This has no effect on well-behaved predicates; the
    ranges:: versions are unaffected because their wrappers already return
    bool.

            PR libstdc++/125981

    libstdc++-v3/ChangeLog:

            * include/bits/stl_algobase.h (__find_if): Force the predicate
            result to bool so that non-boolean_testable predicates cannot
            cause a past-the-end iterator to be dereferenced.
            (__mismatch): Likewise for both overloads.
            * include/bits/stl_heap.h (__push_heap): Likewise for the
            comparator result.
            * testsuite/25_algorithms/find_if/overloaded_logical_ops.cc: New
            test.
            * testsuite/25_algorithms/mismatch/overloaded_logical_ops.cc:
            New test.

    Signed-off-by: Yan Churkin <[email protected]>
    (cherry picked from commit a4ceb702480b9f46dd9b862c81ad7505ca344286)