Improve error boundary handling for unmounted subtrees

A passive effect's cleanup function may throw after an unmount. Prior to this commit, such an error would be ignored. (React would not notify any error boundaries.)

After this commit, React will skip any unmounted boundaries and look for a still-mounted boundary. If one is found, it will call getDerivedStateFromError and/or componentDidCatch (depending on the type of boundary). Unmounted boundaries will be ignored, but as they have been unmounted– this seems appropriate.

packages/react-dom/src/__tests__/ReactErrorBoundaries-test.internal.js

@@ -42,6 +42,7 @@ describe('ReactErrorBoundaries', () => {
     PropTypes = require('prop-types');
     ReactFeatureFlags = require('shared/ReactFeatureFlags');
     ReactFeatureFlags.replayFailedUnitOfWorkWithInvokeGuardedCallback = false;
+    ReactFeatureFlags.skipUnmountedBoundaries = true;
     ReactDOM = require('react-dom');
     React = require('react');
     act = require('react-dom/test-utils').unstable_concurrentAct;
@@ -2473,4 +2474,173 @@ describe('ReactErrorBoundaries', () => {
       'Caught an error: gotta catch em all.',
     );
   });
+
+  it('catches errors thrown in componentWillUnmount', () => {
+    class LocalErrorBoundary extends React.Component {
+      state = {error: null};
+      static getDerivedStateFromError(error) {
+        Scheduler.unstable_yieldValue(
+          `ErrorBoundary static getDerivedStateFromError`,
+        );
+        return {error};
+      }
+      render() {
+        const {children, id, fallbackID} = this.props;
+        const {error} = this.state;
+        if (error) {
+          Scheduler.unstable_yieldValue(`${id} render error`);
+          return <Component id={fallbackID} />;
+        }
+        Scheduler.unstable_yieldValue(`${id} render success`);
+        return children || null;
+      }
+    }
+
+    class Component extends React.Component {
+      render() {
+        const {id} = this.props;
+        Scheduler.unstable_yieldValue('Component render ' + id);
+        return id;
+      }
+    }
+
+    class LocalBrokenComponentWillUnmount extends React.Component {
+      componentWillUnmount() {
+        Scheduler.unstable_yieldValue(
+          'BrokenComponentWillUnmount componentWillUnmount',
+        );
+        throw Error('Expected');
+      }
+
+      render() {
+        Scheduler.unstable_yieldValue('BrokenComponentWillUnmount render');
+        return 'broken';
+      }
+    }
+
+    const container = document.createElement('div');
+
+    ReactDOM.render(
+      <LocalErrorBoundary id="OuterBoundary" fallbackID="OuterFallback">
+        <Component id="sibling" />
+        <LocalErrorBoundary id="InnerBoundary" fallbackID="InnerFallback">
+          <LocalBrokenComponentWillUnmount />
+        </LocalErrorBoundary>
+      </LocalErrorBoundary>,
+      container,
+    );
+
+    expect(container.firstChild.textContent).toBe('sibling');
+    expect(container.lastChild.textContent).toBe('broken');
+    expect(Scheduler).toHaveYielded([
+      'OuterBoundary render success',
+      'Component render sibling',
+      'InnerBoundary render success',
+      'BrokenComponentWillUnmount render',
+    ]);
+
+    ReactDOM.render(
+      <LocalErrorBoundary id="OuterBoundary" fallbackID="OuterFallback">
+        <Component id="sibling" />
+      </LocalErrorBoundary>,
+      container,
+    );
+
+    // React should skip over the unmounting boundary and find the nearest still-mounted boundary.
+    expect(container.firstChild.textContent).toBe('OuterFallback');
+    expect(container.lastChild.textContent).toBe('OuterFallback');
+    expect(Scheduler).toHaveYielded([
+      'OuterBoundary render success',
+      'Component render sibling',
+      'BrokenComponentWillUnmount componentWillUnmount',
+      'ErrorBoundary static getDerivedStateFromError',
+      'OuterBoundary render error',
+      'Component render OuterFallback',
+    ]);
+  });
+
+  it('catches errors thrown while detaching refs', () => {
+    class LocalErrorBoundary extends React.Component {
+      state = {error: null};
+      static getDerivedStateFromError(error) {
+        Scheduler.unstable_yieldValue(
+          `ErrorBoundary static getDerivedStateFromError`,
+        );
+        return {error};
+      }
+      render() {
+        const {children, id, fallbackID} = this.props;
+        const {error} = this.state;
+        if (error) {
+          Scheduler.unstable_yieldValue(`${id} render error`);
+          return <Component id={fallbackID} />;
+        }
+        Scheduler.unstable_yieldValue(`${id} render success`);
+        return children || null;
+      }
+    }
+
+    class Component extends React.Component {
+      render() {
+        const {id} = this.props;
+        Scheduler.unstable_yieldValue('Component render ' + id);
+        return id;
+      }
+    }
+
+    class LocalBrokenCallbackRef extends React.Component {
+      _ref = ref => {
+        Scheduler.unstable_yieldValue('LocalBrokenCallbackRef ref ' + !!ref);
+        if (ref === null) {
+          throw Error('Expected');
+        }
+      };
+
+      render() {
+        Scheduler.unstable_yieldValue('LocalBrokenCallbackRef render');
+        return <div ref={this._ref}>ref</div>;
+      }
+    }
+
+    const container = document.createElement('div');
+
+    ReactDOM.render(
+      <LocalErrorBoundary id="OuterBoundary" fallbackID="OuterFallback">
+        <Component id="sibling" />
+        <LocalErrorBoundary id="InnerBoundary" fallbackID="InnerFallback">
+          <LocalBrokenCallbackRef />
+        </LocalErrorBoundary>
+      </LocalErrorBoundary>,
+      container,
+    );
+
+    expect(container.firstChild.textContent).toBe('sibling');
+    expect(container.lastChild.textContent).toBe('ref');
+    expect(Scheduler).toHaveYielded([
+      'OuterBoundary render success',
+      'Component render sibling',
+      'InnerBoundary render success',
+      'LocalBrokenCallbackRef render',
+      'LocalBrokenCallbackRef ref true',
+    ]);
+
+    ReactDOM.render(
+      <LocalErrorBoundary id="OuterBoundary" fallbackID="OuterFallback">
+        <Component id="sibling" />
+      </LocalErrorBoundary>,
+      container,
+    );
+
+    // React should skip over the unmounting boundary and find the nearest still-mounted boundary.
+    expect(container.firstChild.textContent).toBe('OuterFallback');
+    expect(container.lastChild.textContent).toBe('OuterFallback');
+    expect(Scheduler).toHaveYielded([
+      'OuterBoundary render success',
+      'Component render sibling',
+      'LocalBrokenCallbackRef ref false',
+      'ErrorBoundary static getDerivedStateFromError',
+      'OuterBoundary render error',
+      'Component render OuterFallback',
+    ]);
+  });
 });