Is there a way to specify type aliases for variadic arg functions

[vaderkos]

Is there any way to achieve proper inference of variadic arguments using aliases?

a should be fun(a: table, b: string, c: integer): boolean but instead it's fun(...: table): boolean

I've also tried but it didn't work

--- @alias Predicate1<A> fun(a: A): boolean
--- @alias Predicate2<A, B> fun(a: A, b: B): boolean
--- @alias Predicate3<A, B, C> fun(a: A, b: B, c: C): boolean
--- @alias Predicate4<A, B, C, D> fun(a: A, b: B, c: C, d: D): boolean

--- @alias Predicate<A, B, C, D>
--- | Predicate1<A>
--- | Predicate2<A, B>
--- | Predicate3<A, B, C>
--- | Predicate4<A, B, C, D>

[tomlau10]

AFAIK, there can only be one type for variadic arg i.e. if you write ...: A => it expects all variadic args to be of type A

For your specific use case which you at most have 4 args, I tested around and you can just write it as:

--- @alias Predicate<A, B, C, D> fun(a: A, b: B, c: C, d: D): boolean

---@type Predicate<table, string, integer>
local function test1(a, b, c)
    --> a: table, b: string, c: integer
    return true
end

---@type Predicate<integer>
local function test2(a)
    --> a: integer
    return false
end

Although in this case when you hover over test2, it will be shown as:

local test2: Predicate<integer>
function (a: integer, b: <B>, c: <C>, d: <D>)
  -> boolean

[vaderkos]

My use case rather involved any number of arguments

[tomlau10]

Then it's just not supported currently in LuaLS I believe. 😕 It assumes the ... to be homogeneous (same type), which you can only specific 1 type for it.

If you still would like to use the @alias method, you can define as many arguments as you can. The annotation for table.unpack is also somewhat done in this way: https://github.com/LuaLS/lua-language-server/blob/24b9faa66332fca9f0df6e552ae9f3ca24c01821/meta/template/table.lua#L66-L85

• instead of writing @return ...T (which means all are of the same generic type T
• it uses @return T1, T2, xxx to support up to 10 different inferred return value type

[vaderkos]

Looks like a hack..