Automatically Profile roots when DevTools is present

packages/react-reconciler/src/ReactFiber.js

@@ -35,6 +35,7 @@ import {
 } from 'shared/ReactTypeOfWork';
 import getComponentName from 'shared/getComponentName';
 
+import {isDevToolsPresent} from './ReactFiberDevToolsHook';
 import {NoWork} from './ReactFiberExpirationTime';
 import {NoContext, AsyncMode, ProfileMode, StrictMode} from './ReactTypeOfMode';
 import {
@@ -345,7 +346,15 @@ export function createWorkInProgress(
 }
 
 export function createHostRootFiber(isAsync: boolean): Fiber {
-  const mode = isAsync ? AsyncMode | StrictMode : NoContext;
+  let mode = isAsync ? AsyncMode | StrictMode : NoContext;
+
+  if (enableProfilerTimer && isDevToolsPresent) {
+    // Always collect profile timings when DevTools are present.
+    // This enables DevTools to start capturing timing at any point–
+    // Without some nodes in the tree having empty base times.
+    mode |= ProfileMode;
+  }
+
   return createFiber(HostRoot, null, null, mode);
 }
 

packages/react-reconciler/src/ReactFiberDevToolsHook.js

@@ -31,6 +31,9 @@ function catchErrors(fn) {
   };
 }
 
+export const isDevToolsPresent =
+  typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ !== 'undefined';
+
 export function injectInternals(internals: Object): boolean {
   if (typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ === 'undefined') {
     // No DevTools

packages/react-test-renderer/src/ReactTestRenderer.js

@@ -29,6 +29,7 @@ import {
   Profiler,
 } from 'shared/ReactTypeOfWork';
 import invariant from 'shared/invariant';
+import ReactVersion from 'shared/ReactVersion';
 
 import * as ReactTestHostConfig from './ReactTestHostConfig';
 import * as TestRendererScheduling from './ReactTestRendererScheduling';
@@ -510,4 +511,14 @@ const ReactTestRendererFiber = {
   unstable_setNowImplementation: TestRendererScheduling.setNowImplementation,
 };
 
+// Enable ReactTestRenderer to be used to test DevTools integration.
+TestRenderer.injectIntoDevTools({
+  findFiberByHostInstance: (() => {
+    throw new Error('TestRenderer does not support findFiberByHostInstance()');
+  }: any),
+  bundleType: __DEV__ ? 1 : 0,
+  version: ReactVersion,
+  rendererPackageName: 'react-test-renderer',
+});
+
 export default ReactTestRendererFiber;

packages/react/src/__tests__/ReactProfilerDevToolsIntegration-test.internal.js

@@ -0,0 +1,111 @@
+/**
+ * Copyright (c) 2013-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @emails react-core
+ */
+
+'use strict';
+
+describe('ReactProfiler DevTools integration', () => {
+  let React;
+  let ReactFeatureFlags;
+  let ReactTestRenderer;
+  let AdvanceTime;
+  let advanceTimeBy;
+  let hook;
+  let mockNow;
+
+  const mockNowForTests = () => {
+    let currentTime = 0;
+
+    mockNow = jest.fn().mockImplementation(() => currentTime);
+
+    ReactTestRenderer.unstable_setNowImplementation(mockNow);
+    advanceTimeBy = amount => {
+      currentTime += amount;
+    };
+  };
+
+  beforeEach(() => {
+    global.__REACT_DEVTOOLS_GLOBAL_HOOK__ = hook = {
+      inject: () => {},
+      onCommitFiberRoot: jest.fn((rendererId, root) => {}),
+      onCommitFiberUnmount: () => {},
+      supportsFiber: true,
+    };
+
+    jest.resetModules();
+
+    ReactFeatureFlags = require('shared/ReactFeatureFlags');
+    ReactFeatureFlags.enableProfilerTimer = true;
+    React = require('react');
+    ReactTestRenderer = require('react-test-renderer');
+
+    mockNowForTests();
+
+    AdvanceTime = class extends React.Component {
+      static defaultProps = {
+        byAmount: 10,
+        shouldComponentUpdate: true,
+      };
+      shouldComponentUpdate(nextProps) {
+        return nextProps.shouldComponentUpdate;
+      }
+      render() {
+        // Simulate time passing when this component is rendered
+        advanceTimeBy(this.props.byAmount);
+        return this.props.children || null;
+      }
+    };
+  });
+
+  it('should auto-Profile all fibers if the DevTools hook is detected', () => {
+    const App = ({multiplier}) => {
+      advanceTimeBy(2);
+      return (
+        <React.unstable_Profiler id="Profiler" onRender={onRender}>
+          <AdvanceTime byAmount={3 * multiplier} shouldComponentUpdate={true} />
+          <AdvanceTime
+            byAmount={7 * multiplier}
+            shouldComponentUpdate={false}
+          />
+        </React.unstable_Profiler>
+      );
+    };
+
+    const onRender = jest.fn(() => {});
+    const rendered = ReactTestRenderer.create(<App multiplier={1} />);
+
+    expect(hook.onCommitFiberRoot).toHaveBeenCalledTimes(1);
+
+    // Measure observable timing using the Profiler component.
+    // The time spent in App (above the Profiler) won't be included in the durations,
+    // But needs to be accounted for in the offset times.
+    expect(onRender).toHaveBeenCalledTimes(1);
+    expect(onRender).toHaveBeenCalledWith('Profiler', 'mount', 10, 10, 2, 12);
+    onRender.mockClear();
+
+    // Measure unobservable timing required by the DevTools profiler.
+    // At this point, the base time should include both:
+    // The time 2ms in the App component itself, and
+    // The 10ms spend in the Profiler sub-tree beneath.
+    expect(rendered.root.findByType(App)._currentFiber().treeBaseTime).toBe(12);
+
+    rendered.update(<App multiplier={2} />);
+
+    // Measure observable timing using the Profiler component.
+    // The time spent in App (above the Profiler) won't be included in the durations,
+    // But needs to be accounted for in the offset times.
+    expect(onRender).toHaveBeenCalledTimes(1);
+    expect(onRender).toHaveBeenCalledWith('Profiler', 'update', 6, 13, 14, 20);
+
+    // Measure unobservable timing required by the DevTools profiler.
+    // At this point, the base time should include both:
+    // The initial 9ms for the components that do not re-render, and
+    // The updated 6ms for the component that does.
+    expect(rendered.root.findByType(App)._currentFiber().treeBaseTime).toBe(15);
+  });
+});