Add rules to convert .map(_ => f) to .as(f) and .map(_ => ()) to .void

[custommonkey]

No description provided.

[armanbilge]

Thanks for the PR! We have to be thoughtful about this one I think. The .map(_ => ()) rule is very good 👍

The .map(_ => f) to .as(f) is a bit trickier, because in the first f is lazily evaluated but in the second it is strictly evaluated. This can have implications for performance or recursion. Thus it's only safe to make this substitution if f is a val (and not a lazy val, def, or expression`).

Apologies if that's what you've already coded here (I'm not very good at reading scalafix :) in which case we should definitely add some tests cases for it

[DavidGregory084]

Like @armanbilge says I think we have to be careful here, and without backing up out of the current tree it might be hard to tell whether the _ argument to our AnonymousMap here has already been evaluated.

It's a shame that as is not by-name for this reason.

What do you think about making this case only match on Lit subtypes?

[custommonkey]

Great thank's for the feed back, I'll give that a go.

[DavidGregory084]

This is great 💯 Thanks for the PR!