ERROR: script/core/hint.lua:320: attempt to index a nil value (local 'last')

[tmillr]

How are you using the lua-language-server?

NeoVim 0.10.1
LuaLS 3.9.3

Which OS are you using?

MacOS

What is the issue affecting?

Other

Expected Behaviour

no error

Actual Behaviour

Almost every time I open a file in my editor, I get this error (multiple at a time):

[20:55:15.316][error][#0:script/core/hint.lua:320]: script/core/hint.lua:320: attempt to index a nil value (local 'last')
stack traceback:
	script/core/hint.lua:320: in local 'callback'
	script/parser/guide.lua:770: in function 'parser.guide.eachSourceTypes'
	script/core/hint.lua:288: in upvalue 'semicolonHint'
	script/core/hint.lua:335: in function 'core.hint'
	script/provider/provider.lua:1407: in function <script/provider/provider.lua:1395>
	[C]: in function 'xpcall'
	script/proto/proto.lua:200: in function <script/proto/proto.lua:175>

Reproduction steps

Open an existing Lua file in neovim.

Additional Notes

Config:

require('lspconfig').lua_ls.setup {
  capabilities = require('cmp_nvim_lsp').default_capabilities(),

  settings = {
    Lua = {
      completion = {
        enable = true,
        autoRequire = true,
        keywordSnippet = 'Replace',
        displayContext = 0,
        postfix = '.',
        requireSeparator = '.',
        showParams = true,
      },

      runtime = {
        path = {
          'lua/?.lua',
          'lua/?/init.lua',
        },
        pathStrict = true,
        version = 'LuaJIT',
      },

      diagnostics = {
        enable = true,
        unusedLocalExclude = { '_*' },
      },

      type = {},

      workspace = {
        library = { vim.env.VIMRUNTIME },
      },

      format = { enable = false, defaultConfig = {} },

      hint = {
        enable = true,
        arrayIndex = 'Enabled',
        paramName = 'All',
        paramType = true,
        semicolon = 'All',
        setType = true,
      },

      hover = {
        enable = true,
        enumsLimit = 100,
        expandAlias = true,
      },

      signatureHelp = { enable = true },

      spell = {},

      semantic = {
        enable = false,
        annotation = true,
        keyword = false,
        variable = false,
      },

      telemetry = {
        enable = false,
      },
    },
  },
}

Log File

No response

[clason]

LuaLS 3.9.3

Is this a typo? Latest version is 3.10.3. And please share a concrete (minimal) file to test with. (Just because the error occurred with every file you happened to test with doesn't mean it'll occur with every file. I for example cannot reproduce the error.)

It's also important to show how you

1. installed lua-language-server
2. configured it in Neovim.

[tomlau10]

Insights to this issue

script/core/hint.lua:320: attempt to index a nil value (local 'last')

This logic is under the if case mode == 'All', where local mode = config.get(uri, 'Lua.hint.semicolon')

• lua-language-server/script/core/hint.lua

  Lines 282 to 285 in 2dfb12a

  	local mode = config.get(uri, 'Lua.hint.semicolon')
  	if mode == 'Disable' then
  	return
  	end

• lua-language-server/script/core/hint.lua

  Lines 316 to 320 in 2dfb12a

  	if mode == 'All' then
  	local last = src[#src]
  	results[#results+1] = {
  	text = ';',
  	offset = last.range or last.finish,

=> So this issue happens only when Lua.hint.semicolon is set to All

Reproduction

The default value for Lua.hint.semicolon is SameLine. Once I changed it to All in the .luarc.json (with hint.enable = true of course) of a new workspace, even for an empty file, this error starts to trigger. 🤔

• .luarc.json

{
    "hint.enable": true,
    "hint.semicolon": "All"
}

• then just create an empty test.lua, and observe the error when you open the file
• I used vscode with LuaLS 3.10.3

Analysis

I guess when a block (global scope / if case / etc.) have no statement, the src[] is actually an empty array.

• That's why in the case of empty file, this error already triggers.
  • If the file has at least 1 valid statement say local a => no errors
• Moreover for an empty if block if true then end => error
  • if block with 1 statement if true then local a end => no error

Proposed fix

I believe a simple fix like checking #src > 0 should be enough 🤔 Maybe @tmillr you can test about it and then open PR?

        if mode == 'All' and #src > 0 then
            local last = src[#src]
            ...

[tmillr]

LuaLS 3.9.3

Is this a typo?

No it's not. I use the latest version from nixpkgs unstable, which does seem to lag behind somewhat (because with nix multiple pkgs are updated at once, but only if/when all of them pass tests and don't error). Vim plugins and lua pkgs are usually 1-2 weeks behind.

And please share a concrete (minimal) file to test with. (Just because the error occurred with every file you happened to test with doesn't mean it'll occur with every file. I for example cannot reproduce the error.)

Sorry but I don't have one at this point, but I'll update my OP to include the config I'm using. The error actually appears at "random", but often enough to be annoying. From the error message (attempt to index nil), it appears to be an internal logic error.