False-positive type error: `vim.cmd` callable table flagged as "table cannot match fun(...)"

まず、Neovim の Lua バッファで pcall(vim.cmd, "redrawtabline") を使って診断を再現し、次に __call メタメソッドを持つ呼び出し可能なテーブルについて、LuaLS の診断と型推論を追跡します。呼び出し可能なテーブルが関数値を期待する箇所で受け入れられ、正当な型エラーを隠すことなく、提示された再現で診断が出なくなれば完了です。

How are you using the lua-language-server?

NeoVim

Which OS are you using?

Linux

What is the issue affecting?

Diagnostics/Syntax Checking

Expected Behaviour

lua-language-server should recognize callable tables (with a __call metamethod) as valid function values. Passing Neovim’s vim.cmd to pcall should not raise a type error.

Actual Behaviour

lua-language-server reports a false-positive type error when vim.cmd (a callable table in Neovim) is passed to pcall:

Cannot assign table to parameter fun(...):...unknown
Type table cannot match fun(...):...unknown

Reproduction steps

1. In Neovim, open a Lua buffer (e.g., :new | set ft=lua).

2. Insert the following code:

   -- Works at runtime, but LuaLS flags the next line:
   pcall(vim.cmd, "redrawtabline")
   -- Diagnostic shown by LuaLS:
   -- Cannot assign `table` to parameter `fun(...):...unknown`
   

3. Observe the diagnostic from lua-language-server.

4. Execute the code in Neovim (e.g., :luafile %) to confirm it runs without runtime errors.

Additional Notes

• vim.cmd is a callable table provided by Neovim (implemented via __call metamethod). Direct calls like vim.cmd("redrawtabline") work at runtime. The false-positive only appears when passing vim.cmd as a function value (e.g., to pcall).

• Workarounds:

  -- Wrap in a function
  pcall(function() vim.cmd("redrawtabline") end)
  
  -- or use the typed API
  pcall(vim.api.nvim_cmd, { cmd = "redrawtabline" }, {})
  

• Please treat callable tables as functions for the purpose of type checking / inference.