Remove the warning for setState on unmounted components (#323)

Consistent with upstream React, we should remove the error message when you setState on an unmounted component.

In summary, while it can warn on potential memory leaks, false positives is common and can push people to undesirable workarounds:

function TestComponent:didMount()
    testPromise():andThen(function(newState)
        -- Component might unmount before our promise resolves
        self:setState(newState)
    end)
end
For the full reasoning behind removing the warning, see Dan Abramov's PR: facebook/react#22114

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Roact Changelog
 
 ## Unreleased Changes
+* Removed the warning for `setState` on unmounted components to eliminate false positive warnings, matching upstream React ([#323](https://github.com/Roblox/roact/pull/323)).
 
 ## [1.4.2](https://github.com/Roblox/roact/releases/tag/v1.4.2) (October 6th, 2021)
 * Fixed forwardRef doc code referencing React instead of Roact ([#310](https://github.com/Roblox/roact/pull/310)).

src/Component.lua

@@ -100,21 +100,22 @@ function Component:setState(mapState)
 	local lifecyclePhase = internalData.lifecyclePhase
 
 	--[[
-		When preparing to update, rendering, or unmounting, it is not safe
+		When preparing to update, render, or unmount, it is not safe
 		to call `setState` as it will interfere with in-flight updates. It's
 		also disallowed during unmounting
 	]]
 	if
 		lifecyclePhase == ComponentLifecyclePhase.ShouldUpdate
 		or lifecyclePhase == ComponentLifecyclePhase.WillUpdate
 		or lifecyclePhase == ComponentLifecyclePhase.Render
-		or lifecyclePhase == ComponentLifecyclePhase.WillUnmount
 	then
 		local messageTemplate = invalidSetStateMessages[internalData.lifecyclePhase]
 
 		local message = messageTemplate:format(tostring(internalData.componentClass))
-
 		error(message, 2)
+	elseif lifecyclePhase == ComponentLifecyclePhase.WillUnmount then
+		-- Should not print error message. See https://github.com/facebook/react/pull/22114
+		return
 	end
 
 	local pendingState = internalData.pendingState

src/Component.spec/setState.spec.lua

@@ -109,7 +109,7 @@ return function()
 			expect(result:match("TestComponent")).to.be.ok()
 		end)
 
-		it("should throw when called in willUnmount", function()
+		it("should not throw when called in willUnmount", function()
 			local TestComponent = Component:extend("TestComponent")
 
 			function TestComponent:render()
@@ -125,11 +125,9 @@ return function()
 			local element = createElement(TestComponent)
 			local tree = noopReconciler.mountVirtualTree(element)
 
-			local success, result = pcall(noopReconciler.unmountVirtualTree, tree)
+			local success, _ = pcall(noopReconciler.unmountVirtualTree, tree)
 
-			expect(success).to.equal(false)
-			expect(result:match("willUnmount")).to.be.ok()
-			expect(result:match("TestComponent")).to.be.ok()
+			expect(success).to.equal(true)
 		end)
 
 		it("should remove values from state when the value is None", function()

src/invalidSetStateMessages.lua

@@ -15,12 +15,6 @@ Consider using the didUpdate method instead, or using getDerivedStateFromProps.
 
 Check the definition of willUpdate in the component %q.]]
 
-invalidSetStateMessages[ComponentLifecyclePhase.WillUnmount] = [[
-setState cannot be used in the willUnmount lifecycle method.
-A component that is being unmounted cannot be updated!
-
-Check the definition of willUnmount in the component %q.]]
-
 invalidSetStateMessages[ComponentLifecyclePhase.ShouldUpdate] = [[
 setState cannot be used in the shouldUpdate lifecycle method.
 shouldUpdate must be a pure function that only depends on props and state.