Fix type guard additions

[rob3c]

Description:
This is a fix for the recently-added type guard support in the filter, find, first and last operator typings. Please see the test cases for details of what's working now, and be sure to let me know if I missed anything this time! ;-)

Related issue (if exists):
Apparently, my previous PR in #2119 is being reverted in #2164 due to the important missed case mentioned in #2163. Unfortunately, I didn't receive any notifications about it, but I'm glad I saw it today while lurking through the repo! :-) Hopefully, this PR should address the problem (which I'm embarrased that I missed), and let us keep the new support without breaking previous behavior.

[coveralls]

Coverage remained the same at 97.686% when pulling d9ed68a on rob3c:fix-type-guard-additions into bd56b3c on ReactiveX:master.

[coveralls]

Coverage remained the same at 97.686% when pulling d9ed68a on rob3c:fix-type-guard-additions into bd56b3c on ReactiveX:master.

[jayphelps]

Cc/ @david-driscoll can you review?

[david-driscoll]

I swear I had tried overload ordering the other day to validate if this was possible.

I tried again just now and these changes seem to be working just fine. 👍

cc @saneyuki for an extra set of 👀

[rob3c]

@david-driscoll Yep, the ordering is definitely necessary! It wasn't enough, though, so there are some strategic non-optional function parameters in there, too, to help typescript resolve certain cases.

[tetsuharuohzeki]

@rob3c @david-driscoll

I confirmed that in #2164 we need to write the version which takes predicate returning boolean before to define the one which takes the type guard predicate so that the type inference works correctly for the case of that predicate returning boolean simply. (So we need to define the order of bar<T>() => bar<T, S extends T>())

Is it resolved in this? The current patches are not care about them.

[rob3c]

@saneyuki That's what I originally thought, too.

Surprisingly, it turns out that <T, S extends T> (and <T, S extends T, R> for first and last) needs to be declared before the simpler <T> (and <T, R>) definitions, but it needs to be combined with carefully-defined required/optional parameters, so typescript can distinguish all desired cases. Otherwise, we get the dreaded {} type inferred instead of the actual types for some of them.

[kwonoj]

LGTM

[benlesh]

Thanks so much, @rob3c!!

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.