_queuedResolve, _queuedReject, and _queuedFinally can unnecessarily prevent garbage collection

[Corecii]

roblox-lua-promise/lib/init.lua

Lines 219 to 221 in 9db7364

	_queuedResolve = {},
	_queuedReject = {},
	_queuedFinally = {},

If these are not cleared when a promise completes, this can lead to unnecessary prevention of GC. An :andThen or :finally can include callbacks with upvalue references. Since promises keep strong references to these callbacks, the callbacks and their upvalue references will never be collected.

Here's a realistic example:

local gameReadyPromise = getGameReadyPromise() -- this promise exists forever and completes when all modules have loaded
-- ...
game.Players.PlayerAdded:Connect(function(player)
    gameReadyPromise:andThen(function()
        print(player.Name, "has joined the game!")
        -- load the player into the game
    end)
end)

If any players join the game before gameReadyPromise completes then their player objects can never be garbage collected ultimately due to references originating in _queuedResolve.

Here's a simple test:

local function testGc(callback)
	local gcTester = {}
	local weakRef = setmetatable({gcTester}, {__mode = "v"})
	callback(gcTester)
	gcTester = nil
	wait(10)
	return #weakRef == 0 and "GCed" or "Not GCed"
end

local persistentPromise = Promise.delay(0)

local didGetGced = testGc(function(upvalueGcTester)
	persistentPromise:andThen(function()
		local thisUsesUpvalue = upvalueGcTester
	end)
	persistentPromise:await()
	-- the above callback will *never* be called again, so ideally the callback
	-- and upvalueGcTester would be garbage collected, but they won't be:
end)

print("Did upvalueGcTester get collected?:", didGetGced)

---

This can be solved by clearing out or replacing _queuedResolve, _queuedReject, and _queuedFinally when the promise completes (such as in _finalize).