Thanks to Ian Haywood's review, I've finally managed to land a big upgrade to Twisted's annotations for Deferred: https://github.com/twisted/twisted/pull/11770#issuecomment-1625648066
This is a fix for a bunch of broken annotations within Twisted, both ones that would give you the wrong type sometimes and ones that would give up and give you `Deferred[Any]` when enough information was available to do otherwise, and may help you chase down bugs or otherwise remove spurious type:ignore's from your projects.
In particular, the following methods should provide richer type information now:
maybeDeferred
Deferred.fromFuture
Deferred.addErrback
Deferred.addCallbacks
I would like to note that due to limitations in the way ParamSpec is specified, you'll get less strict validation if you use `addCallbacks`; it's not possible to check argument-signature compatibility for your callbacks with the structure of `addCallbacks`'s signature. Using some combination of `addCallback` and `addErrback` when possible is probably better.
Per the linked comment though, while this is not new in terms of the way Twisted's type annotations should have been working, some of those `Any`s might create situations where you were doing `d.addCallback(...); d.addCallback(...); d.addCallback(...); return d` where you will need to switch to `return d.addCallback(...).addCallback(...).addCallback(...)` in order to get the types to line up properly. (I think if you were literally using `addCallback` you won't have this problem, but combinations of `addCallbacks`, `addErrback`, or `addBoth` might have issues.)
I'm still open to trading reviews, and my next types project (which is considerably smaller in scope and less confusing) is to make FilePath properly generic so you can tell whether `.path` is `str` or `bytes`: https://github.com/twisted/twisted/pull/11823 so if anyone has any interest in reviewing that please let me know what PR you'd like me to look at.
-g
