Lua Language Server Fails to Infer Type When Passing Multiple Return Values to Generic Function

How are you using the lua-language-server?

NeoVim

Which OS are you using?

MacOS

What is the issue affecting?

Type Checking

Expected Behaviour

---@return integer
---@return string
local f = function()
	return 1, "a"
end

---@generic T
---@generic U
---@param t T
---@param u U
---@return U
local g = function(t, u)
	return u
end

local x = g(f())

When the function g is called with the multiple return values of f, the Lua Language Server should infer the type of x based on the second return value of f (string), corresponding to the second generic type parameter (U) in g.

Actual Behaviour

The Lua Language Server fails to infer the type of x. Instead, the type is left unknown.

Reproduction steps

1. Write the following Lua code in an editor with the Lua Language Server enabled:

---@return integer
---@return string
local f = function()
	return 1, "a"
end

---@generic T
---@generic U
---@param t T
---@param u U
---@return U
local g = function(t, u)
	return u
end

local x = g(f())

2. Observe the type inference for x.
3. Note that the type of x is not inferred as string as expected.

Additional Notes

No response

Log File

No response

Comece reproduzindo o snippet de Lua no NeoVim com o Lua Language Server habilitado e inspecione o caminho de inferência de tipos genéricos para chamadas que recebem múltiplos valores de retorno. Considera-se concluído quando a variável x for inferida como string, correspondendo ao segundo valor de retorno de f e ao parâmetro genérico U.