Proposal consider vararg returns as forced optional

How are you using the lua-language-server?

Visual Studio Code Extension (sumneko.lua)

Which OS are you using?

Windows

What is the issue affecting?

Diagnostics/Syntax Checking

Expected Behaviour

I suggest consider vararg returns as optional (can be nil) because no one guarantees that they will be filled in. The same goes for arguments, despite the fact that their type can also be optional or nilable.

If we return at least something, but we don't know the quantity, then the first argument won't be vararg - any, any ....

Thus after that we do not need to additionally specify that the vararg returns is optional.

---@param a string
function test(a) end

---@param ... string
---@return string ...
function f(...) end
local a, b, c = f() --no warn
local a, b, c = f("1")

test(a) --no warn, expected optinal cannot match

---@param ... string?
---@return string? ...
function f(...) end
local a, b, c = f() --no warn
local a, b, c = f("1")

test(a) --warn optinal cannot match

---@param ... string|nil
---@return string|nil ...
function f(...) end
local a, b, c = f() --no warn
local a, b, c = f("1")

test(a) --warn nil cannot match

Actual Behaviour

Vararg arguments are optional, but vararg returns are not.

Reproduction steps

1. Make vararg return of some existing type.
2. It is guaranteed to be infinite - not optional or nil.

Additional Notes

No response

Log File

No response

Lua language server の vararg 引数と戻り値に対する診断および型推論の処理から始め、再現手順と例を動作の指針として使用します。vararg の戻り値が適切に optional または nilable として扱われることを確認し、提示された呼び出しがそれぞれ期待される警告と警告なしの結果を生成することを確認します。