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

Inizia riproducendo lo snippet Lua in NeoVim con Lua Language Server abilitato e ispeziona il percorso di inferenza dei tipi generici per le chiamate che ricevono più valori di ritorno. Il lavoro è completato quando la variabile x viene inferita come string, in corrispondenza del secondo valore di ritorno di f e del parametro generico U.