Native lsp handshake 2

[pr2502]

This is a rewrite of #22 using the new types I've put in. It still needs to be tested properly before I'll be happy with merging it.

Thank you @WhyNotHugo for the idea and for proving it was possible to do this!

TODO

• Basic implementation
• Configuration changes (we no longer use some fields)
• Documentation (README)
• Example minimal editor configuration for testing
  • neovim (via direct TCP)
  • helix (via the builtin proxy client)

[WhyNotHugo]

Thanks for picking this up again!

I tested this with my existing neovim config. I expect it to not-work right away, since my config says raMultiplex, and this now needs to be lspMux.

require'lspconfig'.rust_analyzer.setup{
  cmd = vim.lsp.rpc.connect("127.0.0.1", 27631),
  init_options = {
    raMultiplex = {
      server = "rust-analyzer",
    },
  },
  settings = {
    ['rust-analyzer'] = {
        checkOnSave = {
          command = "clippy",
        },
    }
  }
}

Neovim starts, but give no indication that the LSP has rejected the connection or anything alike. ra-multiple server logs:

 INFO client{port=32894}: client connected
ERROR client{port=32894}: client error: missing `lspMux` in `initializationOptions` in `initialize` request

I think that the connection might not be closed right away when this error happens, so the client is just waiting for a response.

Anyway, I updated raMultiplex to lspMux (with the above camelCase suggestion applied), but that didn't work.

 INFO client{port=45894}: client connected
ERROR client{port=45894}: client error: parse `initialize` request params

Caused by:
    missing field `version`

After some quick debugging, it seems that what is missing here is
lspMux.version. The docs for this say:

/// If you're connecting directly from a client make sure to set the same
/// version reported by `ra-multiplex --version`.

This approach would require reconfiguring the client after
each update. I think it's a bit simpler to just expect version = 1 for now,
and only change this the day backwards-incompatible changes are introduced.

Anyway, I added version to my init_options (which now looks like this:

    init_options = {
      lsp_mux = {
        version = "0.2.2",
        server = "rust-analyzer",
      },
    },

Neovim first complains about this:

LSP[rust_analyzer] received `end` message with no corresponding `begin`

But the LSP then seeks to work fine. I'm not entirely sure what that is about.

---

I then tried opening other projects, but those don't work. Only opening this project works for some mysterious reason (key detail: the ra-multiplex server has as current working directory the root of this project).

 INFO instance{pid=10904}: spawned langauge server server="rust-analyzer" args=[] cwd="file:///home/hugo/src/git.sr.ht/~whynothugo/shotman"
 INFO instance{pid=10904}: initialized server
ERROR instance{pid=10904}: stderr line=[ERROR rust_analyzer::config] failed to find any projects in [AbsPathBuf("/home/hugo/src/git.sr.ht/~whynothugo/shotman")]
ERROR instance{pid=10904}: stderr line=[ERROR rust_analyzer::main_loop] FetchWorkspaceError:
ERROR instance{pid=10904}: stderr line=rust-analyzer failed to discover workspace
 INFO client{port=37310}: initialized client
ERROR instance{pid=10904}: stderr line=[ERROR rust_analyzer::main_loop] FetchWorkspaceError:
ERROR instance{pid=10904}: stderr line=rust-analyzer failed to discover workspace

Neovim shows:

LSP[rust_analyzer] Failed to discover workspace.
Consider adding the `Cargo.toml` of the workspace to the [`linkedProjects`](https://rust-analyzer.github.io/manual.html#rust-analyzer.linkedProjects) setting.

Failed to load workspaces.

The same happens with any other project.

Never mind this last part: this is a bug due to my sandboxing the language servers. I think that previous implementations of ra-multiplex would run the LSP with the workspace directory as cwd, but this implementation does not.

[pr2502]

I consider this mergeable now, if you want to test it again you're welcome, I'll wait a few days anyway. I've changed the exact protocol again, a working configuration example is in examples/neovim/init.lua now.

Also I'd like to figure out how to test the examples (at least that they successfully connect) in CI so I don't forget to update them when/if something changes again.

[WhyNotHugo]

Seems to work fine with the same neovim setup that I mentioned above.

[WhyNotHugo]

... or via the lspMux initialisation options.

(this is non-blocking here tho).

[WhyNotHugo]

Seeing this error when neovim tries to connect:

 INFO client{port=48934}: client connected
ERROR client{port=48934}: client error: parse `initialize` request params

Caused by:
    missing field `method`

On 752fe68

[WhyNotHugo]

Never mind the above; I was missing method = "connect", in my config again for some reason. What do you think of making this parameter optional (with default "connect")?

Neovim now prints this error when first connecting to the LSP:

LSP[rust_analyzer] received `end` message with no corresponding `begin`

Everything seems to work okay regardless.

[pr2502]

I wonder where does that error come from because I haven't seen it with the config in this repository.

[WhyNotHugo]

I'll debug that error when I have some spare time. It's harmless, apparently. Thanks for implementing this.