[Bug libstdc++/100187] New: ranges::search_n helper lambda misses forwarding return type

[hewillk at gmail dot com via Gcc-bugs]

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

            Bug ID: 100187
           Summary: ranges::search_n helper lambda misses forwarding
                    return type
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hewillk at gmail dot com
  Target Milestone: ---

ranges_algo.h#L565:

auto __value_comp = [&] <typename _Rp> (_Rp&& __arg) {
  return std::__invoke(__pred, std::forward<_Rp>(__arg), __value);
};

__value_comp misses forwarding the return type (-> decltype(auto)) which made
the following unnecessary failed:

#include <algorithm>

struct Bool {
  operator bool() { return true; };
  Bool() = default;
  Bool(const Bool&) = delete;
};

int main() {
  Bool b;
  std::vector v{1, 0};
  std::ranges::search_n(v, 1, 1, [&](auto, auto) -> Bool& { return b; });
}

https://godbolt.org/z/zjn8Gz3c5