[Bug libstdc++/115145] New: Help lambda in rewritten std::variant comparisons does not specify return type

[hewillk at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115145

            Bug ID: 115145
           Summary: Help lambda in rewritten std::variant comparisons does
                    not specify return type
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hewillk at gmail dot com
  Target Milestone: ---

..which can be an regression:

#include <variant>

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

struct Elem {
  Bool& operator==(const Elem&) const;
};

int main() {
  std::variant<Elem> v;
  return v == v;
}

https://godbolt.org/z/14q14TrYW