Add csharp lsp support

[Dispersia]

OmniSharp is the defacto LSP for C#, so this just adds it as the default. Tested on Windows/Linux

[Philipp-M]

I don't think the --hostPID is needed and it also needs the actual pid, which I don't think is added by helix?
I'm not sure about the rest of the parameters, my (working) configuration looks a little bit different.

This is my current language configuration (NixOS via home-manager)

{
  name = "c-sharp";
  language-server = { command = "omnisharp"; args = [ "-l" "Error" "--languageserver" "-z" ]; };
}

[Dispersia]

Thanks for taking a look.
Stdio is a more feature-full version, as it allows two way communication compared to the http side:
https://github.com/OmniSharp/omnisharp-roslyn/blob/8f045ddc1922a48ddb9dbe2009e902d1c61453d2/src/OmniSharp.Host/CommandLineApplication.cs

however as for -l Error, I don't believe we would want to limit the logging output to at least less than Warning. OmniSharp will warn on things like package version collisions, things being restored as .net framework, etc, which are all warnings that you wouldn't get as just Error. I also went through the source for http/stdio/cli and couldn't find what the -z is for, do you have a link for the docs for it? https://github.com/OmniSharp/omnisharp-roslyn/blob/8f045ddc1922a48ddb9dbe2009e902d1c61453d2/src/OmniSharp.Host/CommandLineApplication.cs

and it seems you're right about hostPID, I had it auto fill in neovim, but it was working and I assume helix just closes the subprocess when it terminates, so I removed it.

Let me know what you think. Thanks!

[Philipp-M]

Ok good to know, I agree with the logging output, let's keep it default.

Regarding -z:
https://github.com/OmniSharp/omnisharp-roslyn/blob/master/doc/Using-Omnisharp.md#one-based-indexes

[the-mikedavis]

Could you commit the changes from cargo xtask docgen? That should fix the CI

[Dispersia]

Haha, -z was even in the link I posted, i just completely glossed over it somehow.

And thanks, pushed the doc update!

[the-mikedavis]

lgtm 🎉