Forward traced-component ref

Cannot be merged yet, since enzyme@3.3.0 currently breaks on a React.forwardRef with an 'Enzyme Internal Error: unknown node with tag 14' (see issue enzymejs/enzyme#1604).

src/traceLifecycle.jsx

@@ -4,7 +4,7 @@ import PropTypes from 'prop-types';
 
 import * as constants from './constants';
 import * as ActionCreators from './redux/actionCreators';
-import { withDeprecationWarning } from './util';
+import * as util from './util';
 import LifecyclePanel from './components/LifecyclePanel';
 import { MConstructor, MShouldUpdate, MRender, MDidMount,
          MDidUpdate, MWillUnmount, MSetState, MGetDerivedState,
@@ -16,7 +16,7 @@ export const resetInstanceIdCounters = () => {
   Object.keys(instanceIdCounters).forEach((k) => delete instanceIdCounters[k]);
 };
 
-export const clearInstanceIdCounters = withDeprecationWarning(
+export const clearInstanceIdCounters = util.withDeprecationWarning(
   constants.DEPRECATED_CLEAR_COUNTERS,
   resetInstanceIdCounters
 );
@@ -46,11 +46,11 @@ export default function traceLifecycle(ComponentToTrace) {
     constructor(props, context) {
       props.trace(MConstructor);
       super(props, context);
-      this.LifecyclePanel = withDeprecationWarning(
+      this.LifecyclePanel = util.withDeprecationWarning(
         constants.DEPRECATED_THIS_LIFECYCLE_PANEL,
         props.LifecyclePanel
       );
-      this.trace = withDeprecationWarning(
+      this.trace = util.withDeprecationWarning(
         constants.DEPRECATED_THIS_TRACE,
         props.trace
       );
@@ -175,7 +175,15 @@ export default function traceLifecycle(ComponentToTrace) {
     }
 
     render() {
-      return <TracedComponent LifecyclePanel={this.LifecyclePanel} trace={this.trace} {...this.props}/>;
+      const { forwardedRef, ...nonRefProps } = this.props;
+      return (
+        <TracedComponent
+          ref={forwardedRef}
+          LifecyclePanel={this.LifecyclePanel}
+          trace={this.trace}
+          {...nonRefProps}
+        />
+      );
     }
 
     // Get store directly from context, to prevent introducing extra `Connect` component.
@@ -198,5 +206,11 @@ export default function traceLifecycle(ComponentToTrace) {
     delete TracedComponent.prototype.componentWillUpdate;
   }
 
-  return hoistStatics(TracingComponent, ComponentToTrace);
+  const TracingComponentHoisted = hoistStatics(TracingComponent, ComponentToTrace);
+
+  // Prior to v16.4, React.forwardRef triggered unnecessary renders, causing infinite loops.
+  // (see https://github.com/facebook/react/pull/12690)
+  return util.reactVersionIsAtLeast(16, 4)
+    ? React.forwardRef((props, ref) => <TracingComponentHoisted {...props} forwardedRef={ref}/>)
+    : TracingComponentHoisted;
 }

src/util.js

@@ -1,7 +1,13 @@
+import React from 'react';
 import * as constants from './constants';
 
 export const padZeroes = (width, n) => ('' + n).padStart(width, '0');
 
+export const reactVersionIsAtLeast = (vMajorRequired, vMinorRequired) => {
+  const [, vMajor, vMinor] = React.version.match(/^(\d+)\.(\d+)/);
+  return +vMajor > vMajorRequired || +vMajor === vMajorRequired && vMinor >= vMinorRequired;
+};
+
 export const getTimeStamp = () => {
   const now = new Date();
   return `[${padZeroes(2, now.getHours())}:${padZeroes(2, now.getMinutes())}:` +

test/integration.test.jsx

@@ -53,6 +53,20 @@ describe('traceLifecycle', () => {
   it('preserves static properties', () => {
     expect(TracedChild.staticProperty).toBe('a static property');
   });
+
+  // TODO: Untested because of Enzyme failure on React.forwardRef (https://github.com/airbnb/enzyme/issues/1604)
+  it('forwards refs', () => {
+    const refSpy = jest.fn();
+    const RefWrapper = () => (
+      <VisualizerProvider>
+        <TracedChild ref={refSpy}/>
+      </VisualizerProvider>
+    );
+    const refWrapper = mount(<RefWrapper/>);
+    const childInstance = refWrapper.find(TracedChild).childAt(0).instance();
+
+    expect(refSpy).toHaveBeenCalledWith(childInstance);
+  });
 });
 
 describe('LifecyclePanel', () => {