feat(lsp): add tcp support

[mfussenegger]

The plan is to make it possible to have a fully decoupled transport - in addition to TCP it should also be possible to have a "same process" transport (e.g. that null-ls could utilize)

Language servers like Godot only support TCP and currently require workarounds
like socat.

Native TCP support will also allow us to use a dummy server in the tests. Opposed to the fake-lsp-server process it would have the advantage that the server behavior could be part of a test case, as a fake tcp server can run in the same process. Currently the expected notifications and responses are split off in a separate file.

Used like:

vim.lsp.start({ name = 'godot', cmd = vim.lsp.rpc.connect('127.0.0.1', 6008) })

closes #11911

[mfussenegger]

@jose-elias-alvarez Could you have a look at this to check if this would allow null-ls to stop monkey-patching rpc.start?

This PR would allow cmd to be a function that will receive the dispatchers and must return a table with notify, request, is_closing and terminate. (The handle is no longer exposed and is_closing/terminate is used by the lsp module instead)

---

For everyone else: This still needs tests, but otherwise I think it's ready for some feedback.

[jose-elias-alvarez]

From a null-ls perspective this looks great! This should be more or less a drop-in replacement for us (I’m away from a PC for the next week or so but will test this as soon as I can).

[eschmidscs]

Hi

I guess I just need some help here. I'm all newbie, lua, neovim, lsp...
I'm trying to use this for a language server that just uses some port available.

So instead of

vim.lsp.start({name="lsp", cmd=vim.lsp.rpc.connect(host, port)})

I try to do the following (simplified):

vim.lsp.start({
  name="lsp",
  cmd=function()
    start_lsp()
    port=get_lsp_port()
    return vim.lsp.rpc.connect(host, port)
  end
})

This fails with

Error executing lua callback: /usr/share/nvim/runtime/filetype.lua:20: Vim(append):Error executing lua callback: /usr/share/nvim/runtime/lua/vim/lsp.lua:1283: attempt to index upvalue 'rpc' (a function value)

It looks like something local should not be so, but even removing all this did not help.
If I just remove the function and keep the vim.lsp.rpc.connect it works.
Can you give me some hint what is wrong?

Or: Is this the completely wrong attempt? How should I get the port after server start? When should the server be started?

[clason]

Sorry, but this is not a support forum -- usage questions should be asked on https://app.element.io/#/room/#neovim:matrix.org or https://neovim.discourse.group.

[eschmidscs]

I'll ask on discourse. I started here because it seems directly related to this PR (at least on how to use the tcp stuff).

[neovim-discourse]

This pull request has been mentioned on Neovim Discourse. There might be relevant details there:

https://neovim.discourse.group/t/starting-order-for-tcp-based-lsp-lua-error-attempt-to-index-upvalue/3108/1