https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85813
--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to Mathias Stearn from comment #7) > > Simply returning an empty exception_ptr is what happened before the PR 64241 > > change, so what we do now retains that behaviour. That might be the main > > reason for it. > > Silently dropping errors always skeeves me out. I'm not sure if anyone is > well served by the current behavior. If it were up to me (and I know it > isn't) I'd make that case call std::terminate() or similar rather than > returning the "no error" value. That seems consistent with the behavior of > the __throw* functions, but it is a breaking change. Or even better, since > gcc seems fine throwing through functions marked noexcept in -fno-exceptions > TUs, maybe in the (very rare) case where copying/moving an exception throws > inside an -fno-exceptions TU, just let it bubble out. > > > ::new (__e) _Ex(std::forward<_Ex>(__ex)); > > Should that be std::move(__ex)? That would move from an lvalue if called as: E e; std::make_exception_ptr<E&>(e); I don't know if that's valid (I sent an email to the LWG reflector about that a few minutes ago). > I don't know why, but make_exception_ptr > takes the exception by value rather than forwarding ref. Probably so it decays (which "throw e;" will do anyway). > I guess > forward<_Ex> is fine either way, and will stay correct if that defect gets > fixed. It just seemed odd to forward a value so I thought I'd mention it. > > > Mix-and-match works if the function gets inlined. > > Do you think this case warrants a [[gnu::always_inline]]? Given the Without thinking about it too deeply, no I don't think it should have that. It could have negative consequences on the optimization of other code around the call to make_exception_ptr (which might be more important, non-error handling code, that should be inlined in preference to the error-handling path). > sensitive nature of error handling, it seems pretty bad if a correct usage > of make_exception_ptr() could be silently transformed to return the "no > error" value just by linking in a bad library. Even if that library never > dynamically executes make_exception_ptr(). I know I'd hate to be called in > to debug that issue... > > I'm going to go make sure no code we link with uses -fno-exceptions! Rather than always_inline a better option might be to give it a different mangled name when exceptions are disabled (or just not declare it at all, but it might be too late for that as it would be a breaking change). That would ensure the return-null version never gets chosen by the linker to replace the real version.
