validate-tree

Validates a rojo-esque tree definition like so:

Demo

local projectTree = {
    ["$className"] = "Folder",
    NumItems = {
        ["$className"] = "IntValue",
        Data = "Folder", -- This is shorthand for { ["$className"] = "Folder" }
    }
}

function g(o)
    o.NumItems.Value += 1
    return 0
end

function f(o: Instance)
    if validateTree(o, projectTree) then
        print(o.NumItems.Data:GetFullName()) -- Good
        g(o) -- Good
    end
    o.NumItems.Data:GetFullName() -- error!
    g(o) -- error!

    promiseTree(o, projectTree):andThen(function(project)
        print(project.NumItems.Value)
    end)
end

The first parameter must be an Instance (or extend from it). The second parameter must be an object tree similar to ones considered valid by Rojo. Every tree must have a $className member, and can have any number of keys which represent the name of a child instance, which should have a corresponding value which is this same kind of tree. There is also a shorthand syntax, seen above with Folder: "Folder", which is equivalent to Folder: { $className: "Folder" }.