vim.lsp.buf.formatting_sync() fails with `attempt to index a nil value`

[tyrion]

Executing :lua vim.lsp.buf.formatting_sync() sometimes fails with attempt to index a nil value
at

neovim/runtime/lua/vim/lsp/buf.lua

Line 142 in d17e508

result = result[1].result

I am not a lua expert and I do not know how to reproduce this with nvim -u NORC. However, I tried to debug this by making a small lua file test.lua and then executing it in the current buffer with :luafile. This shows that sometimes the result variable is inside the 2 key, instead of 1.

-- dump copied from https://stackoverflow.com/a/27028488/641317
function dump(o)
   if type(o) == 'table' then
      local s = '{ '
      for k,v in pairs(o) do
         if type(k) ~= 'number' then k = '"'..k..'"' end
         s = s .. '['..k..'] = ' .. dump(v) .. ','
      end
      return s .. '} '
   else
      return tostring(o)
   end
end

local params = require'vim.lsp.util'.make_formatting_params()
local result = vim.lsp.buf_request_sync(0, "textDocument/formatting", params)

print(dump(result))
-- shows: { [2] = { ["result"] = { } ,} ,}

This seems to happen only when I open two different files that uses two different language server. Then the problem happens on the second one.
Not sure what this index here is meant to represent. My guess is that it seems the index of the language server used.

• nvim --version:

  NVIM v0.5.0-dev
  Build type: Release
  LuaJIT 2.1.0-beta3
  Compilation: 
  Compiled by nixbld
  Features: +acl +iconv +tui
  

  git rev: a061d53

• language server name/version: typescript-language-server v0.4.0

• Operating system/version: nixos

nvim -c ":checkhealth nvim nvim_lsp"

health#nvim#check

Configuration

• WARNING: Missing user config file: /home/tyrion/.config/nvim/init.vim
  • ADVICE:
    • :help |init.vim|

Performance

• OK: Build type: Release

Remote Plugins

• OK: Up to date

terminal

• INFO: key_backspace (kbs) terminfo entry: key_backspace=\177
• INFO: key_dc (kdch1) terminfo entry: key_dc=\E[3~
• INFO: $COLORTERM='truecolor'

health#nvim_lsp#check

Checking language server protocol configuration

• INFO: tsserver: configuration checked.
• INFO: svelte_lsp: configuration checked.

lsp.log

[ DEBUG ] 2020-11-05T20:39:58+0100 ] ...m-unwrapped-0.5.0-799/share/nvim/runtime/lua/vim/lsp.lua:666 ] "LSP[tsserver]" "client.request" 2 "textDocument/formatting" { options = { insertSpaces = true, tabSize = 4 }, textDocument = { uri = "file:///home/tyrion/src/kschema/src/main.ts" }} <function 1> 3
[ DEBUG ] 2020-11-05T20:39:58+0100 ] ...wrapped-0.5.0-799/share/nvim/runtime/lua/vim/lsp/rpc.lua:376 ] "rpc.send.payload" { id = 5, jsonrpc = "2.0", method = "textDocument/formatting", params = { options = { insertSpaces = true, tabSize = 4 }, textDocument = { uri = "file:///home/tyrion/src/kschema/src/main.ts" } }}
[ DEBUG ] 2020-11-05T20:39:58+0100 ] ...wrapped-0.5.0-799/share/nvim/runtime/lua/vim/lsp/rpc.lua:477 ] "decoded" { id = 5, jsonrpc = "2.0", result = {}}

[fsouza]

Yeah, buf_request_sync uses the client_id as the key and we assume it's [1] here, which is wrong. The correct approach is probably to use next(result) instead of result[1] in formatting_sync.

Here's where the result is set to the client_id:

neovim/runtime/lua/vim/lsp.lua

Lines 1067 to 1070 in d17e508

	local function _callback(err, _method, result, client_id)
	request_results[client_id] = { error = err, result = result }
	result_count = result_count + 1
	end

[tyrion]

I would happily open a PR, however I basically never used lua. Let me know if I should do it anyway. This is what I came up with to fix the issue:

  local util = require 'vim.lsp.util'

  function _G.formatting_sync(options, timeout_ms)
    local params = util.make_formatting_params(options)
    local result = vim.lsp.buf_request_sync(0, "textDocument/formatting", params, timeout_ms)
    if not result then return end
    local index, value = next(result)
    result = value.result
    if not result then return end
    vim.lsp.util.apply_text_edits(result)
  end

[fsouza]

Sent #13233.