Add named hooks support to react-devtools-inline (facebook#22263)

This commit builds on PR facebook#22260 and makes the following changes:
* Adds a DevTools feature flag for named hooks support. (This allows us to disable it entirely for a build via feature flag.)
* Adds a new Suspense cache for dynamically imported modules. (This allows a component to suspend while importing an external code chunk– like the hook names parsing code).
* DevTools supports a hookNamesModuleLoaderFunction param to import the hook names module. I wish this could be handles as part of the react-devtools-shared package, but I'm not sure how to configure Webpack (4) to serve the chunk from react-devtools-inline. This seemed like a reasonable workaround.

The PR also contains an additional unrelated change:
* Removes pre-fetch optimization (added in DevTools: Improve named hooks network caching facebook#22198). This optimization was mostly only important for cases where sources needed to be re-downloaded, something which we can now avoid in most cases¹ thanks to using cached responses already loaded by the page. (I tested this locally on Facebook and this change has no negative performance impact. There is still some overhead from serializing the JS through the Bridge but that's constant between the two approaches.)

¹ The case where we don't benefit from cached responses is when DevTools are opened after the page has already loaded certain scripts. This seems uncommon enough that I don't think it justified the added complexity of prefetching.

packages/react-devtools-extensions/src/main.js

@@ -287,32 +287,30 @@ function createPanelIfReactLoaded() {
           };
         }
 
+        // TODO (Webpack 5) Hopefully we can remove this prop after the Webpack 5 migration.
+        const hookNamesModuleLoaderFunction = () =>
+          import('react-devtools-inline/hookNames');
+
         root = createRoot(document.createElement('div'));
 
         render = (overrideTab = mostRecentOverrideTab) => {
           mostRecentOverrideTab = overrideTab;
-          import('react-devtools-shared/src/hooks/parseHookNames').then(
-            ({parseHookNames, prefetchSourceFiles, purgeCachedMetadata}) => {
-              root.render(
-                createElement(DevTools, {
-                  bridge,
-                  browserTheme: getBrowserTheme(),
-                  componentsPortalContainer,
-                  enabledInspectedElementContextMenu: true,
-                  fetchFileWithCaching,
-                  loadHookNames: parseHookNames,
-                  overrideTab,
-                  prefetchSourceFiles,
-                  profilerPortalContainer,
-                  purgeCachedHookNamesMetadata: purgeCachedMetadata,
-                  showTabBar: false,
-                  store,
-                  warnIfUnsupportedVersionDetected: true,
-                  viewAttributeSourceFunction,
-                  viewElementSourceFunction,
-                }),
-              );
-            },
+          root.render(
+            createElement(DevTools, {
+              bridge,
+              browserTheme: getBrowserTheme(),
+              componentsPortalContainer,
+              enabledInspectedElementContextMenu: true,
+              fetchFileWithCaching,
+              hookNamesModuleLoaderFunction,
+              overrideTab,
+              profilerPortalContainer,
+              showTabBar: false,
+              store,
+              warnIfUnsupportedVersionDetected: true,
+              viewAttributeSourceFunction,
+              viewElementSourceFunction,
+            }),
           );
         };
 

packages/react-devtools-extensions/webpack.config.js

@@ -52,6 +52,7 @@ module.exports = {
     path: __dirname + '/build',
     publicPath: '/build/',
     filename: '[name].js',
+    chunkFilename: '[name].chunk.js',
   },
   node: {
     // Don't define a polyfill on window.setImmediate

packages/react-devtools-inline/README.md

@@ -64,6 +64,23 @@ const DevTools = initialize(contentWindow);
 
 ## Examples
 
+### Supporting named hooks
+
+DevTools can display hook "names" for an inspected component, although determining the "names" requires loading the source (and source-maps), parsing the code, and infering the names based on which variables hook values get assigned to. Because the code for this is non-trivial, it's lazy-loaded only if the feature is enabled.
+
+To configure this package to support this functionality, you'll need to provide a prop that dynamically imports the extra functionality:
+```js
+// Follow code examples above to configure the backend and frontend.
+// When rendering DevTools, the important part is to pass a 'hookNamesModuleLoaderFunction' prop.
+const hookNamesModuleLoaderFunction = () => import('react-devtools-inline/hookNames');
+
+// Render:
+<DevTools
+  hookNamesModuleLoaderFunction={hookNamesModuleLoaderFunction}
+  {...otherProps}
+/>;
+```
+
 ### Configuring a same-origin `iframe`
 
 The simplest way to use this package is to install the hook from the parent `window`. This is possible if the `iframe` is not sandboxed and there are no cross-origin restrictions.

packages/react-devtools-inline/hookNames.js

@@ -0,0 +1 @@
+module.exports = require('./dist/hookNames');

packages/react-devtools-inline/package.json

@@ -20,7 +20,10 @@
     "prepublish": "yarn run build",
     "start": "cross-env NODE_ENV=development webpack --config webpack.config.js --watch"
   },
-  "dependencies": {},
+  "dependencies": {
+    "source-map-js": "^0.6.2",
+    "sourcemap-codec": "^1.4.8"
+  },
   "devDependencies": {
     "@babel/core": "^7.11.1",
     "@babel/plugin-proposal-class-properties": "^7.10.4",

packages/react-devtools-inline/src/hookNames.js

@@ -0,0 +1,9 @@
+/** @flow */
+
+import {
+  parseHookNames,
+  parseSourceAndMetadata,
+  purgeCachedMetadata,
+} from 'react-devtools-shared/src/hooks/parseHookNames';
+
+export {parseHookNames, parseSourceAndMetadata, purgeCachedMetadata};

packages/react-devtools-inline/webpack.config.js

@@ -37,10 +37,12 @@ module.exports = {
   entry: {
     backend: './src/backend.js',
     frontend: './src/frontend.js',
+    hookNames: './src/hookNames.js',
   },
   output: {
     path: __dirname + '/dist',
     filename: '[name].js',
+    chunkFilename: '[name].chunk.js',
     library: '[name]',
     libraryTarget: 'commonjs2',
   },

packages/react-devtools-shared/src/config/DevToolsFeatureFlags.core-fb.js

@@ -15,7 +15,7 @@
 
 export const enableProfilerChangedHookIndices = true;
 export const isInternalFacebookBuild = true;
-
+export const enableNamedHooksFeature = false;
 export const consoleManagedByDevToolsDuringStrictMode = false;
 
 /************************************************************************

packages/react-devtools-shared/src/config/DevToolsFeatureFlags.core-oss.js

@@ -15,7 +15,7 @@
 
 export const enableProfilerChangedHookIndices = false;
 export const isInternalFacebookBuild = false;
-
+export const enableNamedHooksFeature = false;
 export const consoleManagedByDevToolsDuringStrictMode = false;
 
 /************************************************************************

packages/react-devtools-shared/src/config/DevToolsFeatureFlags.default.js

@@ -15,5 +15,5 @@
 
 export const enableProfilerChangedHookIndices = false;
 export const isInternalFacebookBuild = false;
-
+export const enableNamedHooksFeature = true;
 export const consoleManagedByDevToolsDuringStrictMode = true;

packages/react-devtools-shared/src/config/DevToolsFeatureFlags.extension-fb.js

@@ -15,7 +15,7 @@
 
 export const enableProfilerChangedHookIndices = true;
 export const isInternalFacebookBuild = true;
-
+export const enableNamedHooksFeature = true;
 export const consoleManagedByDevToolsDuringStrictMode = true;
 
 /************************************************************************

packages/react-devtools-shared/src/config/DevToolsFeatureFlags.extension-oss.js

@@ -15,7 +15,7 @@
 
 export const enableProfilerChangedHookIndices = true;
 export const isInternalFacebookBuild = false;
-
+export const enableNamedHooksFeature = true;
 export const consoleManagedByDevToolsDuringStrictMode = true;
 
 /************************************************************************

packages/react-devtools-shared/src/devtools/views/Components/FetchFileWithCachingContext.js

@@ -0,0 +1,18 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+import {createContext} from 'react';
+
+export type FetchFileWithCaching = (url: string) => Promise<string>;
+export type Context = FetchFileWithCaching | null;
+
+const FetchFileWithCachingContext = createContext<Context>(null);
+FetchFileWithCachingContext.displayName = 'FetchFileWithCachingContext';
+
+export default FetchFileWithCachingContext;

packages/react-devtools-shared/src/devtools/views/Components/HookNamesModuleLoaderContext.js

@@ -0,0 +1,22 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+import type {Thenable} from 'shared/ReactTypes';
+
+import {createContext} from 'react';
+import typeof * as ParseHookNamesModule from 'react-devtools-shared/src/hooks/parseHookNames';
+
+export type HookNamesModuleLoaderFunction = () => Thenable<ParseHookNamesModule>;
+export type Context = HookNamesModuleLoaderFunction | null;
+
+// TODO (Webpack 5) Hopefully we can remove this context entirely once the Webpack 5 upgrade is completed.
+const HookNamesModuleLoaderContext = createContext<Context>(null);
+HookNamesModuleLoaderContext.displayName = 'HookNamesModuleLoaderContext';
+
+export default HookNamesModuleLoaderContext;

packages/react-devtools-shared/src/devtools/views/Components/InspectedElementContext.js

@@ -30,8 +30,11 @@ import {
   hasAlreadyLoadedHookNames,
   loadHookNames,
 } from 'react-devtools-shared/src/hookNamesCache';
-import HookNamesContext from 'react-devtools-shared/src/devtools/views/Components/HookNamesContext';
+import {loadModule} from 'react-devtools-shared/src/dynamicImportCache';
+import FetchFileWithCachingContext from 'react-devtools-shared/src/devtools/views/Components/FetchFileWithCachingContext';
+import HookNamesModuleLoaderContext from 'react-devtools-shared/src/devtools/views/Components/HookNamesModuleLoaderContext';
 import {SettingsContext} from '../Settings/SettingsContext';
+import {enableNamedHooksFeature} from 'react-devtools-feature-flags';
 
 import type {HookNames} from 'react-devtools-shared/src/types';
 import type {ReactNodeList} from 'shared/ReactTypes';
@@ -64,16 +67,17 @@ export type Props = {|
 
 export function InspectedElementContextController({children}: Props) {
   const {selectedElementID} = useContext(TreeStateContext);
-  const {
-    fetchFileWithCaching,
-    loadHookNames: loadHookNamesFunction,
-    prefetchSourceFiles,
-    purgeCachedMetadata,
-  } = useContext(HookNamesContext);
+  const fetchFileWithCaching = useContext(FetchFileWithCachingContext);
   const bridge = useContext(BridgeContext);
   const store = useContext(StoreContext);
   const {parseHookNames: parseHookNamesByDefault} = useContext(SettingsContext);
 
+  // parseHookNames has a lot of code.
+  // Embedding it into a build makes the build large.
+  // This function enables DevTools to make use of Suspense to lazily import() it only if the feature will be used.
+  // TODO (Webpack 5) Hopefully we can remove this indirection once the Webpack 5 upgrade is completed.
+  const hookNamesModuleLoader = useContext(HookNamesModuleLoaderContext);
+
   const refresh = useCacheRefresh();
 
   // Temporarily stores most recently-inspected (hydrated) path.
@@ -113,24 +117,40 @@ export function InspectedElementContextController({children}: Props) {
     setParseHookNames(parseHookNamesByDefault || alreadyLoadedHookNames);
   }
 
+  const purgeCachedMetadataRef = useRef(null);
+
   // Don't load a stale element from the backend; it wastes bridge bandwidth.
   let hookNames: HookNames | null = null;
   let inspectedElement = null;
   if (!elementHasChanged && element !== null) {
     inspectedElement = inspectElement(element, state.path, store, bridge);
 
-    if (parseHookNames || alreadyLoadedHookNames) {
-      if (
-        inspectedElement !== null &&
-        inspectedElement.hooks !== null &&
-        loadHookNamesFunction !== null
-      ) {
-        hookNames = loadHookNames(
-          element,
-          inspectedElement.hooks,
-          loadHookNamesFunction,
-          fetchFileWithCaching,
-        );
+    if (enableNamedHooksFeature) {
+      if (typeof hookNamesModuleLoader === 'function') {
+        if (parseHookNames || alreadyLoadedHookNames) {
+          const hookNamesModule = loadModule(hookNamesModuleLoader);
+          if (hookNamesModule !== null) {
+            const {
+              parseHookNames: loadHookNamesFunction,
+              purgeCachedMetadata,
+            } = hookNamesModule;
+
+            purgeCachedMetadataRef.current = purgeCachedMetadata;
+
+            if (
+              inspectedElement !== null &&
+              inspectedElement.hooks !== null &&
+              loadHookNamesFunction !== null
+            ) {
+              hookNames = loadHookNames(
+                element,
+                inspectedElement.hooks,
+                loadHookNamesFunction,
+                fetchFileWithCaching,
+              );
+            }
+          }
+        }
       }
     }
   }
@@ -163,14 +183,11 @@ export function InspectedElementContextController({children}: Props) {
       inspectedElementRef.current !== inspectedElement
     ) {
       inspectedElementRef.current = inspectedElement;
-
-      if (typeof prefetchSourceFiles === 'function') {
-        prefetchSourceFiles(inspectedElement.hooks, fetchFileWithCaching);
-      }
     }
-  }, [inspectedElement, prefetchSourceFiles]);
+  }, [inspectedElement]);
 
   useEffect(() => {
+    const purgeCachedMetadata = purgeCachedMetadataRef.current;
     if (typeof purgeCachedMetadata === 'function') {
       // When Fast Refresh updates a component, any cached AST metadata may be invalid.
       const fastRefreshScheduled = () => {

packages/react-devtools-shared/src/devtools/views/Components/InspectedElementHooksTree.js

@@ -22,8 +22,11 @@ import styles from './InspectedElementHooksTree.css';
 import useContextMenu from '../../ContextMenu/useContextMenu';
 import {meta} from '../../../hydration';
 import {getHookSourceLocationKey} from 'react-devtools-shared/src/hookNamesCache';
-import {enableProfilerChangedHookIndices} from 'react-devtools-feature-flags';
-import HookNamesContext from 'react-devtools-shared/src/devtools/views/Components/HookNamesContext';
+import {
+  enableNamedHooksFeature,
+  enableProfilerChangedHookIndices,
+} from 'react-devtools-feature-flags';
+import HookNamesModuleLoaderContext from 'react-devtools-shared/src/devtools/views/Components/HookNamesModuleLoaderContext';
 
 import type {InspectedElement} from './types';
 import type {HooksNode, HooksTree} from 'react-debug-tools/src/ReactDebugHooks';
@@ -53,8 +56,6 @@ export function InspectedElementHooksTree({
 }: HooksTreeViewProps) {
   const {hooks, id} = inspectedElement;
 
-  const {loadHookNames: loadHookNamesFunction} = useContext(HookNamesContext);
-
   // Changing parseHookNames is done in a transition, because it suspends.
   // This value is done outside of the transition, so the UI toggle feels responsive.
   const [parseHookNamesOptimistic, setParseHookNamesOptimistic] = useState(
@@ -65,6 +66,8 @@ export function InspectedElementHooksTree({
     toggleParseHookNames();
   };
 
+  const hookNamesModuleLoader = useContext(HookNamesModuleLoaderContext);
+
   const hookParsingFailed = parseHookNames && hookNames === null;
 
   let toggleTitle;
@@ -85,7 +88,8 @@ export function InspectedElementHooksTree({
       <div className={styles.HooksTreeView}>
         <div className={styles.HeaderRow}>
           <div className={styles.Header}>hooks</div>
-          {loadHookNamesFunction !== null &&
+          {enableNamedHooksFeature &&
+            typeof hookNamesModuleLoader === 'function' &&
             (!parseHookNames || hookParsingFailed) && (
               <Toggle
                 className={hookParsingFailed ? styles.ToggleError : null}