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

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.

首先，在 Neovim Lua 缓冲区中使用 pcall(vim.cmd, "redrawtabline") 重现该诊断，然后跟踪带有 __call 元方法的可调用表的 LuaLS 诊断和类型推断。完成的标准是：在需要函数值的地方接受可调用表，同时不隐藏真正的类型错误，并且给出的重现不再产生诊断。