Fix bindings leak (#40)

Author: LordOfSpelunky

modules/react-roblox/src/client/__tests__/ReactRobloxBindings.roblox.spec.luau

@@ -98,6 +98,34 @@ it("should not return the same root twice", function()
 	jestExpect(reactRobloxRoot).never.toBe(reactRobloxRoot2)
 end)
 
+it("should unsubscribe from bindings when unmounted", function()
+	local counterBinding, setCounter = React.createBinding(0)
+	local renderCount = 0
+	local function Component()
+		return React.createElement("TextLabel", {
+			Text = counterBinding:map(function(counter)
+				renderCount += 1
+				return tostring(counter)
+			end),
+		})
+	end
+	ReactRoblox.act(function()
+		reactRobloxRoot:render(React.createElement(Component))
+	end)
+	jestExpect(renderCount).toBe(1)
+	ReactRoblox.act(function()
+		reactRobloxRoot:render(React.createElement(Component))
+	end)
+	jestExpect(renderCount).toBe(2)
+	setCounter(1)
+	jestExpect(renderCount).toBe(3)
+	ReactRoblox.act(function()
+		reactRobloxRoot:unmount()
+	end)
+	setCounter(2)
+	jestExpect(renderCount).toBe(3)
+end)
+
 describe("useBinding hook", function()
 	it("returns the same binding object each time", function()
 		local captureBinding = jest.fn()

modules/react-roblox/src/client/roblox/RobloxComponentProps.luau

@@ -306,15 +306,24 @@ local function updateProperties(
 	end
 end
 
+local function cleanupBindings(domElement: HostInstance)
+	local instanceBindings = instanceToBindings[domElement]
+	if instanceBindings ~= nil then
+		for _, disconnectBinding in instanceBindings do
+			disconnectBinding()
+		end
+		instanceToBindings[domElement] = nil
+	end
+end
+
 -- ROBLOX deviation: Clear out references to components when they unmount so we
 -- avoid leaking memory when they're removed
 local function cleanupHostComponent(domElement: HostInstance)
 	if instanceToEventManager[domElement] ~= nil then
 		instanceToEventManager[domElement] = nil
 	end
-	if instanceToBindings[domElement] ~= nil then
-		instanceToBindings[domElement] = nil
-	end
+
+	cleanupBindings(domElement)
 
 	-- ROBLOX https://jira.rbx.com/browse/LUAFDN-718: Tables are somehow ending up
 	-- in this function that expects Instances. In that case, we won't be able to
@@ -328,9 +337,8 @@ local function cleanupHostComponent(domElement: HostInstance)
 		if instanceToEventManager[descElement] ~= nil then
 			instanceToEventManager[descElement] = nil
 		end
-		if instanceToBindings[descElement] ~= nil then
-			instanceToBindings[descElement] = nil
-		end
+		
+		cleanupBindings(descElement)
 		removeAllTags(domElement)
 	end
 end