Show highlight when element is selected in React devtools

Summary:
Changelog:
[General][Changed] - Copied and refactored the current devtools highlighting code from Inspector into its own module and add to the top level `AppContainer`. The effect is that the highlight stills shows without Inspector opened.

This diff copies the current devtools highlighting logic from Inspector into a module and add to the top level `AppContainer`. The effect is without Inspector opened, the highlight will still show.

## Context
This is the first diff for "Component Tab Automatically Highlight Elements". The idea is to replicate the behavior on Web to RN.

## Behavior
on Web:
- highlight shows whenever an element in the component list is hovered
- Selecting an element doesn't keeps the highlight showing.

on RN (before this diff):
- when RN inspector opens: selecting an element keeps the highlight showing
- when RN inspector closes: stop showing highlihgintg.

on RN(this diff)
- selecting an element keeps the highlight showing

## TODO
- See if highlighting event can be sent on hover, instead of when an element is selected.

Reviewed By: lunaruan

Differential Revision: D38568135

fbshipit-source-id: d168874677d08a9c5526a7f896943579da804565

Libraries/Inspector/DevtoolsHighlighter.js

@@ -0,0 +1,80 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ * @flow
+ */
+
+import ElementBox from './ElementBox';
+import * as React from 'react';
+const {useEffect, useState} = React;
+
+const hook = window.__REACT_DEVTOOLS_GLOBAL_HOOK__;
+
+export default function DevtoolsHighlighter(): React.Node {
+  const [inspected, setInspected] = useState(null);
+  useEffect(() => {
+    let devToolsAgent = null;
+    let hideTimeoutId = null;
+
+    function onAgentHideNativeHighlight() {
+      // we wait to actually hide in order to avoid flicker
+      clearTimeout(hideTimeoutId);
+      hideTimeoutId = setTimeout(() => {
+        setInspected(null);
+      }, 100);
+    }
+
+    function onAgentShowNativeHighlight(node: any) {
+      clearTimeout(hideTimeoutId);
+      // Shape of `node` is different in Fabric.
+      const component = node.canonical ?? node;
+
+      component.measure((x, y, width, height, left, top) => {
+        setInspected({
+          frame: {left, top, width, height},
+        });
+      });
+    }
+
+    function cleanup() {
+      const currentAgent = devToolsAgent;
+      if (currentAgent != null) {
+        currentAgent.removeListener(
+          'hideNativeHighlight',
+          onAgentHideNativeHighlight,
+        );
+        currentAgent.removeListener(
+          'showNativeHighlight',
+          onAgentShowNativeHighlight,
+        );
+        currentAgent.removeListener('shutdown', cleanup);
+        devToolsAgent = null;
+      }
+    }
+
+    function _attachToDevtools(agent: Object) {
+      devToolsAgent = agent;
+      agent.addListener('hideNativeHighlight', onAgentHideNativeHighlight);
+      agent.addListener('showNativeHighlight', onAgentShowNativeHighlight);
+      agent.addListener('shutdown', cleanup);
+    }
+
+    hook.on('react-devtools', _attachToDevtools);
+    if (hook.reactDevtoolsAgent) {
+      _attachToDevtools(hook.reactDevtoolsAgent);
+    }
+    return () => {
+      hook.off('react-devtools', _attachToDevtools);
+      cleanup();
+    };
+  }, []);
+
+  if (inspected != null) {
+    return <ElementBox frame={inspected.frame} />;
+  }
+  return null;
+}

Libraries/Inspector/Inspector.js

@@ -144,8 +144,6 @@ class Inspector extends React.Component<
   }
 
   _attachToDevtools = (agent: Object) => {
-    agent.addListener('hideNativeHighlight', this._onAgentHideNativeHighlight);
-    agent.addListener('showNativeHighlight', this._onAgentShowNativeHighlight);
     agent.addListener('shutdown', this._onAgentShutdown);
 
     this.setState({
@@ -153,45 +151,9 @@ class Inspector extends React.Component<
     });
   };
 
-  _onAgentHideNativeHighlight = () => {
-    if (this.state.inspected === null) {
-      return;
-    }
-    // we wait to actually hide in order to avoid flicker
-    this._hideTimeoutID = setTimeout(() => {
-      this.setState({
-        inspected: null,
-      });
-    }, 100);
-  };
-
-  _onAgentShowNativeHighlight = (node: any) => {
-    clearTimeout(this._hideTimeoutID);
-
-    // Shape of `node` is different in Fabric.
-    const component = node.canonical ?? node;
-
-    component.measure((x, y, width, height, left, top) => {
-      this.setState({
-        hierarchy: [],
-        inspected: {
-          frame: {left, top, width, height},
-        },
-      });
-    });
-  };
-
   _onAgentShutdown = () => {
     const agent = this.state.devtoolsAgent;
     if (agent != null) {
-      agent.removeListener(
-        'hideNativeHighlight',
-        this._onAgentHideNativeHighlight,
-      );
-      agent.removeListener(
-        'showNativeHighlight',
-        this._onAgentShowNativeHighlight,
-      );
       agent.removeListener('shutdown', this._onAgentShutdown);
 
       this.setState({devtoolsAgent: null});

Libraries/ReactNative/AppContainer.js

@@ -77,14 +77,19 @@ class AppContainer extends React.Component<Props, State> {
 
   render(): React.Node {
     let logBox = null;
+    let devtoolsHighlighter = null;
     if (__DEV__) {
-      if (
-        !global.__RCTProfileIsProfiling &&
-        !this.props.internal_excludeLogBox
-      ) {
-        const LogBoxNotificationContainer =
-          require('../LogBox/LogBoxNotificationContainer').default;
-        logBox = <LogBoxNotificationContainer />;
+      if (!global.__RCTProfileIsProfiling) {
+        if (!this.props.internal_excludeLogBox) {
+          const LogBoxNotificationContainer =
+            require('../LogBox/LogBoxNotificationContainer').default;
+          logBox = <LogBoxNotificationContainer />;
+        }
+        if (window.__REACT_DEVTOOLS_GLOBAL_HOOK__ != null) {
+          const DevtoolsHighlighter =
+            require('../Inspector/DevtoolsHighlighter').default;
+          devtoolsHighlighter = <DevtoolsHighlighter />;
+        }
       }
     }
 
@@ -118,6 +123,7 @@ class AppContainer extends React.Component<Props, State> {
       <RootTagContext.Provider value={createRootTag(this.props.rootTag)}>
         <View style={styles.appContainer} pointerEvents="box-none">
           {!this.state.hasError && innerView}
+          {devtoolsHighlighter}
           {this.state.inspector}
           {logBox}
         </View>