Fix bailout broken in lazy components due to default props resolving (#…

…18539)

* Add failing tests for lazy components

* Fix bailout broken in lazy components due to default props resolving

We should never compare unresolved props with resolved props. Since comparing
resolved props by reference doesn't make sense, we use unresolved props in that
case. Otherwise, resolved props are used.

* Avoid reassigning props warning when we bailout

packages/react-reconciler/src/ReactFiberBeginWork.js

@@ -856,7 +856,7 @@ function updateClassComponent(
   );
   if (__DEV__) {
     const inst = workInProgress.stateNode;
-    if (inst.props !== nextProps) {
+    if (shouldUpdate && inst.props !== nextProps) {
       if (!didWarnAboutReassigningProps) {
         console.error(
           'It looks like %s is reassigning its own `this.props` while rendering. ' +

packages/react-reconciler/src/ReactFiberClassComponent.js

@@ -997,11 +997,13 @@ function updateClassInstance(
 
   cloneUpdateQueue(current, workInProgress);
 
-  const oldProps = workInProgress.memoizedProps;
-  instance.props =
+  const unresolvedOldProps = workInProgress.memoizedProps;
+  const oldProps =
     workInProgress.type === workInProgress.elementType
-      ? oldProps
-      : resolveDefaultProps(workInProgress.type, oldProps);
+      ? unresolvedOldProps
+      : resolveDefaultProps(workInProgress.type, unresolvedOldProps);
+  instance.props = oldProps;
+  const unresolvedNewProps = workInProgress.pendingProps;
 
   const oldContext = instance.context;
   const contextType = ctor.contextType;
@@ -1029,7 +1031,10 @@ function updateClassInstance(
     (typeof instance.UNSAFE_componentWillReceiveProps === 'function' ||
       typeof instance.componentWillReceiveProps === 'function')
   ) {
-    if (oldProps !== newProps || oldContext !== nextContext) {
+    if (
+      unresolvedOldProps !== unresolvedNewProps ||
+      oldContext !== nextContext
+    ) {
       callComponentWillReceiveProps(
         workInProgress,
         instance,
@@ -1047,7 +1052,7 @@ function updateClassInstance(
   newState = workInProgress.memoizedState;
 
   if (
-    oldProps === newProps &&
+    unresolvedOldProps === unresolvedNewProps &&
     oldState === newState &&
     !hasContextChanged() &&
     !checkHasForceUpdateAfterProcessing()
@@ -1056,15 +1061,15 @@ function updateClassInstance(
     // effect even though we're bailing out, so that cWU/cDU are called.
     if (typeof instance.componentDidUpdate === 'function') {
       if (
-        oldProps !== current.memoizedProps ||
+        unresolvedOldProps !== current.memoizedProps ||
         oldState !== current.memoizedState
       ) {
         workInProgress.effectTag |= Update;
       }
     }
     if (typeof instance.getSnapshotBeforeUpdate === 'function') {
       if (
-        oldProps !== current.memoizedProps ||
+        unresolvedOldProps !== current.memoizedProps ||
         oldState !== current.memoizedState
       ) {
         workInProgress.effectTag |= Snapshot;
@@ -1121,15 +1126,15 @@ function updateClassInstance(
     // effect even though we're bailing out, so that cWU/cDU are called.
     if (typeof instance.componentDidUpdate === 'function') {
       if (
-        oldProps !== current.memoizedProps ||
+        unresolvedOldProps !== current.memoizedProps ||
         oldState !== current.memoizedState
       ) {
         workInProgress.effectTag |= Update;
       }
     }
     if (typeof instance.getSnapshotBeforeUpdate === 'function') {
       if (
-        oldProps !== current.memoizedProps ||
+        unresolvedOldProps !== current.memoizedProps ||
         oldState !== current.memoizedState
       ) {
         workInProgress.effectTag |= Snapshot;

packages/react-reconciler/src/__tests__/ReactLazy-test.internal.js

@@ -343,6 +343,97 @@ describe('ReactLazy', () => {
     expect(root).toMatchRenderedOutput('SiblingB');
   });
 
+  it('resolves defaultProps without breaking bailout due to unchanged props and state, #17151', async () => {
+    class LazyImpl extends React.Component {
+      static defaultProps = {value: 0};
+
+      render() {
+        const text = `${this.props.label}: ${this.props.value}`;
+        return <Text text={text} />;
+      }
+    }
+
+    const Lazy = lazy(() => fakeImport(LazyImpl));
+
+    const instance1 = React.createRef(null);
+    const instance2 = React.createRef(null);
+
+    const root = ReactTestRenderer.create(
+      <>
+        <LazyImpl ref={instance1} label="Not lazy" />
+        <Suspense fallback={<Text text="Loading..." />}>
+          <Lazy ref={instance2} label="Lazy" />
+        </Suspense>
+      </>,
+      {
+        unstable_isConcurrent: true,
+      },
+    );
+    expect(Scheduler).toFlushAndYield(['Not lazy: 0', 'Loading...']);
+    expect(root).not.toMatchRenderedOutput('Not lazy: 0Lazy: 0');
+
+    await Promise.resolve();
+
+    expect(Scheduler).toFlushAndYield(['Lazy: 0']);
+    expect(root).toMatchRenderedOutput('Not lazy: 0Lazy: 0');
+
+    // Should bailout due to unchanged props and state
+    instance1.current.setState(null);
+    expect(Scheduler).toFlushAndYield([]);
+    expect(root).toMatchRenderedOutput('Not lazy: 0Lazy: 0');
+
+    // Should bailout due to unchanged props and state
+    instance2.current.setState(null);
+    expect(Scheduler).toFlushAndYield([]);
+    expect(root).toMatchRenderedOutput('Not lazy: 0Lazy: 0');
+  });
+
+  it('resolves defaultProps without breaking bailout in PureComponent, #17151', async () => {
+    class LazyImpl extends React.PureComponent {
+      static defaultProps = {value: 0};
+      state = {};
+
+      render() {
+        const text = `${this.props.label}: ${this.props.value}`;
+        return <Text text={text} />;
+      }
+    }
+
+    const Lazy = lazy(() => fakeImport(LazyImpl));
+
+    const instance1 = React.createRef(null);
+    const instance2 = React.createRef(null);
+
+    const root = ReactTestRenderer.create(
+      <>
+        <LazyImpl ref={instance1} label="Not lazy" />
+        <Suspense fallback={<Text text="Loading..." />}>
+          <Lazy ref={instance2} label="Lazy" />
+        </Suspense>
+      </>,
+      {
+        unstable_isConcurrent: true,
+      },
+    );
+    expect(Scheduler).toFlushAndYield(['Not lazy: 0', 'Loading...']);
+    expect(root).not.toMatchRenderedOutput('Not lazy: 0Lazy: 0');
+
+    await Promise.resolve();
+
+    expect(Scheduler).toFlushAndYield(['Lazy: 0']);
+    expect(root).toMatchRenderedOutput('Not lazy: 0Lazy: 0');
+
+    // Should bailout due to shallow equal props and state
+    instance1.current.setState({});
+    expect(Scheduler).toFlushAndYield([]);
+    expect(root).toMatchRenderedOutput('Not lazy: 0Lazy: 0');
+
+    // Should bailout due to shallow equal props and state
+    instance2.current.setState({});
+    expect(Scheduler).toFlushAndYield([]);
+    expect(root).toMatchRenderedOutput('Not lazy: 0Lazy: 0');
+  });
+
   it('sets defaultProps for modern lifecycles', async () => {
     class C extends React.Component {
       static defaultProps = {text: 'A'};