RFC: Type states.

[alexmccord]

No description provided.

[Dionysusnu]

Here's a rendered link.

What will this change mean for the following code?

local x: number? = 1
function revertX()
    x = nil
end
revertX()
local y: number = x

This is currently sound (TypeError on y assignment). With this RFC, is it tracked that x could revert to a different value in a callback? The RFC covers some introduced unsoundness with table references modified elsewhere, but that's minor. The case above appears more frequently, especially if x is modified in an event handler (RBXScriptConnection) or there is some yielding call in between.

[zeux]

This PR is closed as part of RFC migration; please see #1074 (comment) for context.