avoid bailing in strict equality (#3884)

src/diff/index.js

@@ -143,10 +143,16 @@ export function diff(
 						) === false) ||
 					newVNode._original === oldVNode._original
 				) {
-					c.props = newProps;
-					c.state = c._nextState;
 					// More info about this here: https://gist.github.com/JoviDeCroock/bec5f2ce93544d2e6070ef8e0036e4e8
-					if (newVNode._original !== oldVNode._original) c._dirty = false;
+					if (newVNode._original !== oldVNode._original) {
+						// When we are dealing with a bail because of sCU we have to update
+						// the props, state and dirty-state.
+						// when we are dealing with strict-equality we don't as the child could still
+						// be dirtied see #3883
+						c.props = newProps;
+						c.state = c._nextState;
+						c._dirty = false;
+					}
 					newVNode._dom = oldVNode._dom;
 					newVNode._children = oldVNode._children;
 					newVNode._children.forEach(vnode => {

test/browser/lifecycles/shouldComponentUpdate.test.js

@@ -858,6 +858,53 @@ describe('Lifecycle methods', () => {
 		// ]);
 	});
 
+	it('should correctly handle double state updates', () => {
+		let updateParent, updateChild;
+		class Parent extends Component {
+			state = { text: 'parent-old' };
+
+			componentDidMount() {
+				updateParent = () => this.setState({ text: 'Parent-NEW' });
+			}
+
+			render() {
+				return (
+					<Fragment>
+						{this.props.children} and {this.state.text}
+					</Fragment>
+				);
+			}
+		}
+
+		class Child extends Component {
+			state = { text: 'child-old' };
+
+			shouldComponentUpdate(nextProps, nextState) {
+				return this.state.text !== nextState.text;
+			}
+
+			componentDidMount() {
+				updateChild = () => this.setState({ text: 'Child-NEW' });
+			}
+
+			render() {
+				return <h1>{this.state.text}</h1>;
+			}
+		}
+
+		render(
+			<Parent>
+				<Child />
+			</Parent>,
+			scratch
+		);
+
+		updateParent();
+		updateChild();
+		rerender();
+		expect(scratch.innerHTML).to.equal('<h1>Child-NEW</h1> and Parent-NEW');
+	});
+
 	it('should maintain the order if memoised component initially rendered empty content', () => {
 		let showText, updateParent;
 		class Child extends Component {