Extract FilePattern to its own library

[eborden]

Shake's FilePattern seems like a useful module. It should be extract into a library so it can be shared by other tools.

This has been mentioned before:
#499
#485
ndmitchell/hlint#402
ndmitchell/hlint#334

[ndmitchell]

Are you going to give this a try?

[ndmitchell]

One thing to note is that Shake supports // patterns mostly as a legacy feature. I suggest the new filepattern package also supports that, but perhaps behind a useLegacyPatterns function, just so Shake can migrate more slowly.

[eborden]

I'm going to give it a go.

[eborden]

First pass to extract the necessary modules:
https://github.com/eborden/filepattern

[eborden]

I've done the work to provide FilePattern and FilePattern.Legacy. As well as opening #551 to begin relying on that library. There is a bit more work in filepattern getting CI running and re-enabling some tests, but should be enough draft work for you to review.

[eborden]

Oh also not sure how you want to handle the filepattern repo. Totally fine to hand it over to you if you'd rather keep maintainer-ship.

[ndmitchell]

Thanks for all the work, I’ll review later. What do you prefer/hope in terms of maintainership? You, me or both seems the possible options.

[eborden]

I think a dual maintainership sounds good. This lib is integral to shake so it is probably good for you to at least have one hand on the wheel.

[eborden]

Popping in here to see if you've had a chance to review.

[ndmitchell]

Alas, not yet - I've penciled in a train journey tomorrow morning to do a thorough review!

[eborden]

@ndmitchell How are you feeling about this initiative?

[ndmitchell]

Still positive, going through it slowly. Unfortunately other things cropped up so it's currently 5th on my 3rd todo list (I work through them all in parallel).

[ndmitchell]

Completed - thanks to your help and constant enthusiasm. https://hackage.haskell.org/package/filepattern is the result, and it's vastly better than the stuff in Shake.

[eborden]

Awesome!

[ndmitchell]

Plan is to wait until filepattern is used in HLint, ideally extensively (there are a few good places it could fit) and then we can sanity test it before turning it loose in Shake.

Once we do turn it lose the plan is make a release with everything but this. Then make a 0.1 bump with just the change to filepattern. Also requires removing // from the documentation.

[ndmitchell]

As it happened, for #642 I needed to use exactly the nice clean and optimised functions that were in filepattern, so I added the dependency. Most FilePattern values are the internal Shake implementation, but this particular one for --lint-watch is the new style. Given it's a debug only feature it shouldn't hurt too much.