Haskell-language-server: Case splitting features

[pepeiborra]

Original Twitter threads: https://twitter.com/Anka213/status/1289724597735063552

Case splitting an equation (in Idris):

How this could be implemented in HLS:

• A code action provider to split equations with an empty rhs
• A completion provider with splitting suggestions for case [..] of

Tools that already do this:

• hackage.haskell.org/package/shplit
• https://hackage.haskell.org/package/ghc-mod-5.8.0.0/docs/GhcMod-Exe-CaseSplit.html

[jneira]

Just in case the references can help, the feature was included in hie (afaik using ghc-mod underneath and using hare by @Avi-D-coder): https://github.com/haskell/haskell-ide-engine/issues/907

[isovector]

@TOTBWF and are tackling this (and other great things!)

[isovector]

It's looking really good! We want to get a little more code automation in before opening a PR.

[pepeiborra]

Wow, that looks fabulous!

[isovector]

Blocked by https://github.com/alanz/ghc-exactprint/issues/91, since it prevents us from to synthesize new terms that respect layout.

[pepeiborra]

Blocked by alanz/ghc-exactprint#91, since it prevents us from to synthesize new terms that respect layout.

Oh no! Please share the ghcide/HLS branch and maybe someone can find a workaround.

[isovector]

@pepeiborra sure! I will be forever in your debt if you can. https://github.com/isovector/haskell-language-server/tree/tactics

Everything is hooked up and working, but TreeTransform (which uses ExactPrint) runs into this issue when trying to insert the generated terms back into the source.