Haskell-language-server: Retrie plugin

[pepeiborra]

http://hackage.haskell.org/package/retrie

Retrie is a modern alternative to HaRe, and possibly better maintained as it is used by Facebook.

It can be used to implement refactorings like:

• Inline functions with --unfold
• Extract functions, with --fold
• Inline and extract type synonyms, with --type-forward and --type-backward

It could be also used to implement renames and moves, but those would require custom scripts.

[pepeiborra]

/cc @xich in case he is already working on this

[alanz]

Yes, I have been wanting to get to this. And also wondering if it should not be used to make the changes from hlint.

[xich]

I'm not working on it myself, but happy to support anyone who does. I would love to see this happen!

@alanz Funny you mention hlint. That was the initial motivation for retrie, but I never got back around to doing the integration. I probably will at some point, if someone doesn't beat me to it.

[alanz]

ping @ndmitchell

[ndmitchell]

HLint uses the refactor data types - https://hackage.haskell.org/package/refact-0.3.0.2/docs/Refact-Types.html - so all that is required is someone to have those supported in retrie. Note that recently @zliu41 has been working to improve these, and there are some known bugs in apply-refact that we currently use to execute these replacements.

[xich]

The Replace constructor from Refact.Types would be quite easy to generate from retrie's writer type:

https://github.com/facebookincubator/retrie/blob/f54706a1c8e4f16ae39e540059cf4e2b33498d18/Retrie/Replace.hs#L86-L90

That is essentially how I do replacements in CPP files already:

https://github.com/facebookincubator/retrie/blob/99256ce6f97c40bb4f3211302a3381eed099ad5e/Retrie/Run.hs#L113

(printCPP splices them into the actual file)

The API for actually running retrie with a custom handler for Replacements is to call run with a custom WriteFn:

https://github.com/facebookincubator/retrie/blob/master/Retrie/Run.hs#L77

See examples of various WriteFns in Retrie.Run module.

[pepeiborra]

I have started working on Retrie integration in the branch https://github.com/pepeiborra/ide/tree/retrie

The branch relies on some upstream changes (https://github.com/facebookincubator/retrie/pull/9) and therefore cannot be merged until those changes are accepted and released.

[TomMD]

Looks like retrie has included @pepeiborra 's changes. From the linked PR:

Just released this as part of retrie-0.1.1.1

So... LGTM?

[pepeiborra]

I want to wait until https://github.com/facebookincubator/retrie/issues/10 lands before resuming this work

[xich]

Ah, sorry! Didn’t realize I was blocking you. I’m afk the next couple days, but once I’m back, let’s try to work out the details.