Add failing test for sCU current props

this.props is not reset when a render is bailed out on.

This can cause potential problems for subsequent calls to shouldComponentUpdate if certain types of comparisons are made between this.props and nextProps.

Author: Brian Vaughn

scripts/fiber/tests-failing.txt

@@ -57,6 +57,9 @@ src/renderers/shared/__tests__/ReactPerf-test.js
 * should not count time in a portal towards lifecycle method
 * should work when measurement starts during reconciliation
 
+src/renderers/shared/fiber/__tests__/ReactIncremental-test.js
+* should restore previous props when work is bailed out before commit
+
 src/renderers/shared/hooks/__tests__/ReactComponentTreeHook-test.js
 * can be retrieved by ID
 

src/renderers/shared/fiber/__tests__/ReactIncremental-test.js

@@ -2021,4 +2021,84 @@ describe('ReactIncremental', () => {
     });
     ReactNoop.flush();
   });
+
+  it('should restore previous props when work is bailed out before commit', () => {
+    let cduNextProps = null;
+    let cduPrevProps = null;
+    let scuNextProps = null;
+    let scuPrevProps = null;
+
+    function SecondChild(props) {
+      return <span>{props.children}</span>;
+    }
+
+    class FirstChild extends React.Component {
+      componentDidUpdate(prevProps, prevState) {
+        cduNextProps = this.props;
+        cduPrevProps = prevProps;
+      }
+      shouldComponentUpdate(nextProps, nextState) {
+        scuNextProps = nextProps;
+        scuPrevProps = this.props;
+        return this.props.children !== nextProps.children;
+      }
+      render() {
+        return <span>{this.props.children}</span>;
+      }
+    }
+
+    class Middle extends React.Component {
+      render() {
+        return (
+          <div>
+            <FirstChild>{this.props.flag}</FirstChild>
+            <SecondChild>{this.props.flag}</SecondChild>
+          </div>
+        );
+      }
+    }
+
+    function Root(props) {
+      return (
+        <div hidden={true}>
+          <Middle {...props} />
+        </div>
+      );
+    }
+
+    // Initial render of the entire tree.
+    // Renders: Root, Middle, FirstChild, SecondChild
+    ReactNoop.render(<Root flag={0} />);
+    ReactNoop.flush();
+
+    // Schedule low priority work to update children.
+    // Renders: Root
+    ReactNoop.render(<Root flag={1} />);
+    ReactNoop.flushDeferredPri(20);
+
+    // Children are now pending rendering.
+    // Give them enough time to partially render.
+    // Renders: Middle, FirstChild
+    ReactNoop.flushDeferredPri(30 + 5);
+
+    // At this point sCU should have been called with previous:0, next:1
+    // Since the render is not completed cDU should not be called yet.
+    expect(scuPrevProps.children).toEqual(0);
+    expect(scuNextProps.children).toEqual(1);
+    expect(cduPrevProps).toEqual(null);
+    expect(cduNextProps).toEqual(null);
+
+    // Then interrupt the partial render with higher priority work.
+    // The in-progress child content will bailout.
+    // Renders: Root, Middle, FirstChild, SecondChild
+    ReactNoop.render(<Root flag={2} />);
+    ReactNoop.flush();
+
+    // At this point, since the low priority work was bailed out on,
+    // sCU and cDU should have been called with previous:0, next:2
+    expect(scuPrevProps.children).toEqual(0);
+    expect(scuNextProps.children).toEqual(2);
+    expect(cduPrevProps.children).toEqual(0);
+    expect(cduNextProps.children).toEqual(2);
+  });
 });