Hot Loading Sourcemaps

Summary:
public

To make sourcemaps work on Hot Loading work, we'll need to be able to serve them for each module that is dynamically replaced. To do so we introduced a new parameter to the bundler, namely `entryModuleOnly` to decide whether or not to process the full dependency tree or just the module associated to the entry file. Also we need to add `//sourceMappingURL` to the HMR updates so that in case of an error the runtime retrieves the sourcemaps for the file on which an error occurred from the server.

Finally, we need to refactor a bit how we load the HMR updates into JSC. Unfortunately, if the code is eval'ed when an error is thrown, the line and column number are missing. This is a bug/missing feature in JSC. To walkaround the issue we need to eval the code on native. This adds a bit of complexity to HMR as for both platforms we'll have to have a thin module to inject code but I don't see any other alternative. when debugging this is not needed as Chrome supports sourceMappingURLs on eval'ed code

Reviewed By: javache

Differential Revision: D2841788

fb-gh-sync-id: ad9370d26894527a151cea722463e694c670227e

react-packager/src/Bundler/Bundle.js

@@ -206,7 +206,7 @@ class Bundle extends BundleBase {
   _getCombinedSourceMaps(options) {
     const result = {
       version: 3,
-      file: 'bundle.js',
+      file: this._getSourceMapFile(),
       sections: [],
     };
 
@@ -246,7 +246,7 @@ class Bundle extends BundleBase {
 
     const mappings = this._getMappings();
     const map = {
-      file: 'bundle.js',
+      file: this._getSourceMapFile(),
       sources: _.pluck(super.getModules(), 'sourcePath'),
       version: 3,
       names: [],
@@ -262,6 +262,12 @@ class Bundle extends BundleBase {
     return eTag;
   }
 
+  _getSourceMapFile() {
+    return this._sourceMapUrl
+      ? this._sourceMapUrl.replace('.map', '.bundle')
+      : 'bundle.js';
+  }
+
   _getMappings() {
     const modules = super.getModules();
 

react-packager/src/Bundler/BundleBase.js

@@ -19,6 +19,10 @@ class BundleBase {
     this._mainModuleId = this._mainModuleName = undefined;
   }
 
+  isEmpty() {
+    return this._modules.length === 0 && this._assets.length === 0;
+  }
+
   getMainModuleId() {
     return this._mainModuleId;
   }

react-packager/src/Bundler/HMRBundle.js

@@ -8,12 +8,17 @@
  */
 'use strict';
 
+const _ = require('underscore');
 const BundleBase = require('./BundleBase');
 const ModuleTransport = require('../lib/ModuleTransport');
 
 class HMRBundle extends BundleBase {
-  constructor() {
+  constructor({sourceURLFn, sourceMappingURLFn}) {
     super();
+    this._sourceURLFn = sourceURLFn
+    this._sourceMappingURLFn = sourceMappingURLFn;
+    this._sourceURLs = [];
+    this._sourceMappingURLs = [];
   }
 
   addModule(resolver, response, module, transformed) {
@@ -21,14 +26,8 @@ class HMRBundle extends BundleBase {
       module,
       transformed.code,
     ).then(({name, code}) => {
-      code = `
-        __accept(
-          '${name}',
-          function(global, require, module, exports) {
-            ${code}
-          }
-        );
-      `;
+      // need to be in single line so that lines match on sourcemaps
+      code = `__accept(${JSON.stringify(name)}, function(global, require, module, exports) { ${code} });`;
 
       const moduleTransport = new ModuleTransport({
         code,
@@ -40,8 +39,22 @@ class HMRBundle extends BundleBase {
       });
 
       super.addModule(moduleTransport);
+      this._sourceMappingURLs.push(this._sourceMappingURLFn(moduleTransport.sourcePath));
+      this._sourceURLs.push(this._sourceURLFn(moduleTransport.sourcePath));
     });
   }
+
+  getModulesCode() {
+    return this._modules.map(module => module.code);
+  }
+
+  getSourceURLs() {
+    return this._sourceURLs;
+  }
+
+  getSourceMappingURLs() {
+    return this._sourceMappingURLs;
+  }
 }
 
 module.exports = HMRBundle;

react-packager/src/Bundler/__tests__/Bundle-test.js

@@ -214,7 +214,7 @@ describe('Bundle', () => {
 
         const sourceMap = otherBundle.getSourceMap({dev: true});
         expect(sourceMap).toEqual({
-          file: 'bundle.js',
+          file: 'test_url',
           version: 3,
           sections: [
             { offset: { line: 0, column: 0 }, map: { name: 'sourcemap foo' } },
@@ -340,7 +340,7 @@ describe('Bundle', () => {
 
 
 function genSourceMap(modules) {
-  var sourceMapGen = new SourceMapGenerator({file: 'bundle.js', version: 3});
+  var sourceMapGen = new SourceMapGenerator({file: 'test_url', version: 3});
   var bundleLineNo = 0;
   for (var i = 0; i < modules.length; i++) {
     var module = modules[i];

react-packager/src/Bundler/index.js

@@ -166,9 +166,58 @@ class Bundler {
     });
   }
 
+  _sourceHMRURL(platform, path) {
+    return this._hmrURL(
+      'http://localhost:8081', // TODO: (martinb) avoid hardcoding
+      platform,
+      'bundle',
+      path,
+    );
+  }
+
+  _sourceMappingHMRURL(platform, path) {
+    // Chrome expects `sourceURL` when eval'ing code
+    return this._hmrURL(
+      '\/\/# sourceURL=',
+      platform,
+      'map',
+      path,
+    );
+  }
+
+  _hmrURL(prefix, platform, extensionOverride, path) {
+    const matchingRoot = this._projectRoots.find(root => path.startsWith(root));
+
+    if (!matchingRoot) {
+      throw new Error('No matching project root for ', path);
+    }
+
+    const extensionStart = path.lastIndexOf('.');
+    let resource = path.substring(
+      matchingRoot.length,
+      extensionStart !== -1 ? extensionStart : undefined,
+    );
+
+    const extension = extensionStart !== -1
+      ? path.substring(extensionStart + 1)
+      : null;
+
+    return (
+      prefix + resource +
+      '.' + extensionOverride + '?' +
+      'platform=' + platform + '&runModule=false&entryModuleOnly=true&hot=true'
+    );
+  }
+
   bundleForHMR(options) {
     return this._bundle({
-      bundle: new HMRBundle(),
+      bundle: new HMRBundle({
+        sourceURLFn: this._sourceHMRURL.bind(this, options.platform),
+        sourceMappingURLFn: this._sourceMappingHMRURL.bind(
+          this,
+          options.platform,
+        ),
+      }),
       hot: true,
       ...options,
     });
@@ -185,6 +234,7 @@ class Bundler {
     platform,
     unbundle: isUnbundle,
     hot: hot,
+    entryModuleOnly,
   }) {
     const findEventId = Activity.startEvent('find dependencies');
     let transformEventId;
@@ -195,6 +245,12 @@ class Bundler {
       bundle.setMainModuleName(response.mainModuleId);
       transformEventId = Activity.startEvent('transform');
 
+      let dependencies;
+      if (entryModuleOnly) {
+        dependencies = response.dependencies.filter(module =>
+          module.path.endsWith(entryFile)
+        );
+      } else {
         const moduleSystemDeps = includeSystemDependencies
           ? this._resolver.getModuleSystemDependencies(
             { dev: isDev, platform, isUnbundle }
@@ -207,6 +263,7 @@ class Bundler {
         bundle.setNumPrependedModules && bundle.setNumPrependedModules(
           response.numPrependedDependencies + moduleSystemDeps.length
         );
+      }
 
       let bar;
       if (process.stdout.isTTY) {

react-packager/src/Server/__tests__/Server-test.js

@@ -144,6 +144,7 @@ describe('processRequest', () => {
         platform: undefined,
         runBeforeMainModule: ['InitializeJavaScriptAppEngine'],
         unbundle: false,
+        entryModuleOnly: false,
       });
     });
   });
@@ -165,6 +166,7 @@ describe('processRequest', () => {
         platform: 'ios',
         runBeforeMainModule: ['InitializeJavaScriptAppEngine'],
         unbundle: false,
+        entryModuleOnly: false,
       });
     });
   });
@@ -321,6 +323,7 @@ describe('processRequest', () => {
           platform: undefined,
           runBeforeMainModule: ['InitializeJavaScriptAppEngine'],
           unbundle: false,
+          entryModuleOnly: false,
         })
       );
     });
@@ -341,6 +344,7 @@ describe('processRequest', () => {
             platform: undefined,
             runBeforeMainModule: ['InitializeJavaScriptAppEngine'],
             unbundle: false,
+            entryModuleOnly: false,
           })
         );
     });

react-packager/src/Server/index.js

@@ -118,6 +118,10 @@ const bundleOpts = declareOpts({
     type: 'boolean',
     default: false,
   },
+  entryModuleOnly: {
+    type: 'boolean',
+    default: false,
+  },
 });
 
 const dependencyOpts = declareOpts({
@@ -527,6 +531,11 @@ class Server {
         false
       ),
       platform: platform,
+      entryModuleOnly: this._getBoolOptionFromQuery(
+        urlObj.query,
+        'entryModuleOnly',
+        false,
+      ),
     };
   }