Feature request: add general support for the Language Server Protocol

[Firehed]

Many languages are starting to add support for the Language Server Protocol, which supports (among other things) getting diagnostic errors on files from the language server. I believe ale could leverage this to get pretty reusable support across many languages, and add support for new languages in the future with relatively little effort.

[w0rp]

Yep, I had planned on doing that for TypeScript, perhaps. Supporting this probably won't be easy, but it'll be worth doing.

My short term plan for TypeScript is to add a linter which grabs results form tsuquyomi, when it's installed, which implements parts of the LSP for TypeScript.

[w0rp]

https://github.com/Microsoft/language-server-protocol/blob/master/protocol.md I recommend reading this, for anyone interested in implementing an LSP client. It took me a while to track that page down. That's the best specification I can find.

[Firehed]

Just FYI, TypeScript (well, tsserver) doesn't appear to actually implement the protocol - although the implementation mechanics will likely be extremely similar.

Broadly, I think the process will look like:

• Spawn server, if one is not already running (this should be the only language-specific thing)
• client/registerCapability
• Send textDocument/didOpen when a document opens
• Send textDocument/didChange with the full buffer contents when a change occurs (it can be done as a series of diffs by the look of it, but that sounds very painful)
• Send textDocument/didSave on save (may need only the above or this, depending on the user's ale settings)
• Listen for textDocument/publishDiagnostics, and display any errors it indicates
• Cleanup work as needed (didClose, stop server, etc)

I'm certainly not an expert on the protocol, but I think that's all that is necessary since a lot of the protocol is for refactoring, IDE hints, etc. Easier said than done, of course, but it may not be too horrible

[w0rp]

I have created the branch tsserver which reports errors using tsserver. The API for tsserver is different from LSP servers, but parts of the logic are roughly the same. I'll experiment with it a bit before merging it into master.

Now I think it would be a good idea to try out a real LSP server for some other language.

[w0rp]

I fixed the way the handling of diagnostic responses figured out which errors are for which buffers for TSServer and merged that into master now. Now others can try it out and I can fix whatever bugs come up.