Bogus error messages "BUG in SwiftNIO, unleakable promise leaked"

[weissi]

If a user accidentally shuts down the ELG before actually being done, they often get

BUG in SwiftNIO (please report), unleakable promise leaked.:486: Fatal error: leaking promise created at (file: "BUG in SwiftNIO (please report), unleakable promise leaked.", line: 486)

which is both

1. wrong (in all cases that I've seen)
2. Misleading

the message should be adjusted to say that it's likely that the EventLoop (which we can actually print!) was likely shut down already (and that it's a bug in NIO if it isn't shut down)

[weissi]

CC @Lukasa

This message is bogus and we need to reword it. Suggestions?

[Lukasa]

Do we think having this message is pulling its weight at all? We already print a message about shutting down the ELG in most of these cases.

[weissi]

Do we think having this message is pulling its weight at all? We already print a message about shutting down the ELG in most of these cases.

Are you suggesting to delete the message entirely and just making it preconditionFailure()? Fine by me, but I'd probably put something like promise of already-shutdown EventLoop leaked or smth.

[Lukasa]

I don't have a strong opinion either way, honestly.