Dependent return value types for declared functions

[PhoenixWhitefire]

I'm trying to implement support for Luau's Analyzer via Luau LSP for Visual Studio Code in my runtime. I've gotten most of the way there, and the main thing left is adding a function which returns a type dependent on it's input, similar to Instance.new in Roblox. I tried looking through Luau LSP's globalTypes.d.luau, but I couldn't figure out how it worked.

Essentially:

local animal = Object.createWithComponent("Deer")
-- type of `animal` should be "Object & Deer", where `Object` and `Deer` are already defined external types
-- `animal` should have the combined members of `Object` and `Deer`

[PhoenixWhitefire]

I think I should ask this on the Luau LSP repository instead

[PhoenixWhitefire]

Here's what I eventually ended up using:

type Creatables = {
    Deer: Deer,
    Fox: Fox,
    Rabbit: Rabbit
}

declare Object: {
    createWithComponent: <T>(T & keyof<Creatables>) -> Object & index<Creatables, T>
}