Table passed across modules flagged by type checker for missing optional property about luau HOT 3 CLOSED

--!strict
local function a()
    return { Start = function() end }
end

local mod = a()

type Service = {
    Start: () -> (),
    OnPlayerAdded: (player: Player) -> ()?,
}

local function Load(service: Service)
end

Load(mod)

local function f()
  return { p = 5, q = "seven" }
end

local function g(t: { p: number, q: number? })
  t.q = 7
end

-- t : { p : number, q : string }
-- u : { p : number }
-- at runtime, u aliases t
local t = f()
local u = t :: { p : number }

g(u) -- at runtime, mutates q to have `7` (and consequently, t)

local q = t.q -- type system thinks `t.q` has type `string`, but at runtime it's a `number`.

local t = { p = 5 }

g(t)