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

首先，在启用 Lua Language Server 的 NeoVim 中复现这段 Lua 代码，并检查接收多个返回值的调用所经过的泛型类型推断路径。完成标准是变量 x 被推断为 string，与 f 的第二个返回值和泛型参数 U 相匹配。