Code formatting

[soywod]

haskell-ide-engine proposes to format the code via brittany. It would be possible to do the same for eg. with purty?

[nwolverson]

I'm as yet unconvinced whether this should be in the language server or something external with editor integration; I guess the fact that there only seems to be 1 option does lean towards simply including it.

Welcome opinions

[soywod]

Well, the text formatting is part of the LSP spec, so I guess it makes sense to add one. For eg. the client Coc.vim has implemented the formatting. No matter the language I use, it will call the format function (if exists) from the language server.

[milesfrain]

A few related links that are mostly related to purty with vscode IDE:

There's a vscode extension for purty formatting:
https://github.com/mvakula/vscode-purty

Discussion on consolidating vscode extensions:
nwolverson/vscode-language-purescript#10

purty issue on integration with vscode:
https://gitlab.com/joneshf/purty/-/issues/124

Discourse thread on purty integration with IDE:
https://discourse.purescript.org/t/purty-ide-integration-to-format-on-save/1272

[andys8]

In my opinion it would be nice to provide a format handler and delegate the work to purty. Fail if not installed. The advantage is that there is no need to configure formatting or have a plugin for putty per editor.

[thomashoneyman]

I'm as yet unconvinced whether this should be in the language server or something external with editor integration; I guess the fact that there only seems to be 1 option does lean towards simply including it.

If we do end up with multiple code formatters that's also not a problem; afaik the language server API is designed to accommodate this. In VSCode, for example, if you have multiple code formatters on your system that can be used for the same language then the editor will ask you to choose which one you want to use (or it can be configured in your settings).

[andys8]

haskell-ide-engine (and haskell-language-server) give the user configuration options to select the formatting provider. elm-language-server does not because there is only elm-format.

One could try to detect if purty is on the PATH and conditionally set the the formatting provider capability but I haven't seen that before. I think it's easier to fail silently (log) or with an user facing error once the user executes code formatting with the language server.

[nwolverson]

I've definitely come around to the idea that we should "just do it" (before the PR :) ), can always make the option enabled in config if required.