Add module scope plugin (facebook#2189)

* Add module scope plugin

* Oops

* Add comments

* Check windows seps too

* More descriptive error

* Document it

packages/react-dev-utils/ModuleScopePlugin.js

@@ -0,0 +1,68 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+'use strict';
+
+const chalk = require('chalk');
+const path = require('path');
+
+class ModuleScopePlugin {
+  constructor(appSrc) {
+    this.appSrc = appSrc;
+  }
+
+  apply(resolver) {
+    const { appSrc } = this;
+    resolver.plugin('file', (request, callback) => {
+      // Unknown issuer, probably webpack internals
+      if (!request.context.issuer) {
+        return callback();
+      }
+      if (
+        // If this resolves to a node_module, we don't care what happens next
+        request.descriptionFileRoot.indexOf('/node_modules/') !== -1 ||
+        request.descriptionFileRoot.indexOf('\\node_modules\\') !== -1 ||
+        // Make sure this request was manual
+        !request.__innerRequest_request
+      ) {
+        return callback();
+      }
+      // Resolve the issuer from our appSrc and make sure it's one of our files
+      // Maybe an indexOf === 0 would be better?
+      const relative = path.relative(appSrc, request.context.issuer);
+      // If it's not in src/ or a subdirectory, not our request!
+      if (relative[0] === '.') {
+        return callback();
+      }
+      // Find path from src to the requested file
+      const requestRelative = path.relative(
+        appSrc,
+        path.resolve(
+          path.dirname(request.context.issuer),
+          request.__innerRequest_request
+        )
+      );
+      // Error if in a parent directory of src/
+      if (requestRelative[0] === '.') {
+        callback(
+          new Error(
+            `You attempted to import ${chalk.cyan(request.__innerRequest_request)} which falls outside of the project ${chalk.cyan('src/')} directory. ` +
+              `Relative imports outside of ${chalk.cyan('src/')} are not supported. ` +
+              `You can either move it inside ${chalk.cyan('src/')}, or add a symlink to it from project's ${chalk.cyan('node_modules/')}.`
+          ),
+          request
+        );
+      } else {
+        callback();
+      }
+    });
+  }
+}
+
+module.exports = ModuleScopePlugin;

packages/react-dev-utils/README.md

@@ -56,6 +56,26 @@ module.exports = {
 }
 ```
 
+
+#### `new ModuleScopePlugin(appSrc: string)`
+
+This Webpack plugin ensures that relative imports from app's source directory don't reach outside of it.
+
+```js
+var path = require('path');
+var ModuleScopePlugin = require('react-dev-utils/ModuleScopePlugin');
+
+
+module.exports = {
+  // ...
+  plugins: [
+    new ModuleScopePlugin(paths.appSrc),
+    // ...
+  ],
+  // ...
+}
+```
+
 #### `new WatchMissingNodeModulesPlugin(nodeModulesPath: string)`
 
 This Webpack plugin ensures `npm install <library>` forces a project rebuild.<br>

packages/react-dev-utils/package.json

@@ -21,6 +21,7 @@
     "getProcessForPort.js",
     "InterpolateHtmlPlugin.js",
     "launchEditor.js",
+    "ModuleScopePlugin.js",
     "openBrowser.js",
     "openChrome.applescript",
     "prepareProxy.js",

packages/react-scripts/config/webpack.config.dev.js

@@ -18,6 +18,7 @@ const CaseSensitivePathsPlugin = require('case-sensitive-paths-webpack-plugin');
 const InterpolateHtmlPlugin = require('react-dev-utils/InterpolateHtmlPlugin');
 const WatchMissingNodeModulesPlugin = require('react-dev-utils/WatchMissingNodeModulesPlugin');
 const eslintFormatter = require('react-dev-utils/eslintFormatter');
+const ModuleScopePlugin = require('react-dev-utils/ModuleScopePlugin');
 const getClientEnvironment = require('./env');
 const paths = require('./paths');
 
@@ -106,6 +107,14 @@ module.exports = {
       // https://www.smashingmagazine.com/2016/08/a-glimpse-into-the-future-with-react-native-for-web/
       'react-native': 'react-native-web',
     },
+    plugins: [
+      // Prevents users from importing files from outside of src/ (or node_modules/).
+      // This often causes confusion because we only process files within src/ with babel.
+      // To fix this, we prevent you from importing files out of src/ -- if you'd like to,
+      // please link the files into your node_modules/ and let module-resolution kick in.
+      // Make sure your source files are compiled, as they will not be processed in any way.
+      new ModuleScopePlugin(paths.appSrc),
+    ],
   },
   module: {
     strictExportPresence: true,

packages/react-scripts/config/webpack.config.prod.js

@@ -18,6 +18,7 @@ const ExtractTextPlugin = require('extract-text-webpack-plugin');
 const ManifestPlugin = require('webpack-manifest-plugin');
 const InterpolateHtmlPlugin = require('react-dev-utils/InterpolateHtmlPlugin');
 const eslintFormatter = require('react-dev-utils/eslintFormatter');
+const ModuleScopePlugin = require('react-dev-utils/ModuleScopePlugin');
 const paths = require('./paths');
 const getClientEnvironment = require('./env');
 
@@ -103,6 +104,14 @@ module.exports = {
       // https://www.smashingmagazine.com/2016/08/a-glimpse-into-the-future-with-react-native-for-web/
       'react-native': 'react-native-web',
     },
+    plugins: [
+      // Prevents users from importing files from outside of src/ (or node_modules/).
+      // This often causes confusion because we only process files within src/ with babel.
+      // To fix this, we prevent you from importing files out of src/ -- if you'd like to,
+      // please link the files into your node_modules/ and let module-resolution kick in.
+      // Make sure your source files are compiled, as they will not be processed in any way.
+      new ModuleScopePlugin(paths.appSrc),
+    ],
   },
   module: {
     strictExportPresence: true,