Support specifying plugins by path

README.md

@@ -609,13 +609,16 @@ config
   .use(WebpackPlugin, args)
 
 // Examples
+
 config
   .plugin('hot')
   .use(webpack.HotModuleReplacementPlugin);
 
+// Plugins can also be specified by their path, allowing the expensive require()s to be
+// skipped in cases where the plugin or webpack configuration won't end up being used.
 config
   .plugin('env')
-  .use(webpack.EnvironmentPlugin, ['NODE_ENV']);
+  .use(require.resolve('webpack/lib/EnvironmentPlugin'), [{ 'VAR': false }]);
 ```
 
 #### Config plugins: modify arguments
@@ -1217,6 +1220,29 @@ config.toString();
 */
 ```
 
+Plugins specified via their path will have their `require()` statement generated
+automatically:
+
+``` js
+config
+  .plugin('env')
+    .use(require.resolve('webpack/lib/ProvidePlugin'), [{ jQuery: 'jquery' }])
+
+config.toString();
+
+/*
+{
+  plugins: [
+    new (require('/foo/bar/src/node_modules/webpack/lib/EnvironmentPlugin.js'))(
+      {
+        jQuery: 'jquery'
+      }
+    )
+  ]
+}
+*/
+```
+
 You can also call `toString` as a static method on `Config` in order to
 modify the configuration object prior to stringifying.
 

src/Config.js

@@ -55,13 +55,17 @@ module.exports = class extends ChainedMap {
           const prefix = `/* ${configPrefix}.plugin('${
             value.__pluginName
           }') */\n`;
-          const constructorName = value.__pluginConstructorName;
+          const constructorExpression = value.__pluginPath
+            ? // The path is stringified to ensure special characters are escaped
+              // (such as the backslashes in Windows-style paths).
+              `(require(${stringify(value.__pluginPath)}))`
+            : value.__pluginConstructorName;
 
-          if (constructorName) {
+          if (constructorExpression) {
             // get correct indentation for args by stringifying the args array and
             // discarding the square brackets.
             const args = stringify(value.__pluginArgs).slice(1, -1);
-            return `${prefix}new ${constructorName}(${args})`;
+            return `${prefix}new ${constructorExpression}(${args})`;
           }
           return (
             prefix +

src/Plugin.js

@@ -39,17 +39,30 @@ module.exports = Orderable(
 
     toConfig() {
       const init = this.get('init');
-      const plugin = this.get('plugin');
+      let plugin = this.get('plugin');
+      const args = this.get('args');
+      let pluginPath = null;
+
+      // Support using the path to a plugin rather than the plugin itself,
+      // allowing expensive require()s to be skipped in cases where the plugin
+      // or webpack configuration won't end up being used.
+      if (typeof plugin === 'string') {
+        pluginPath = plugin;
+        // eslint-disable-next-line global-require, import/no-dynamic-require
+        plugin = require(pluginPath);
+      }
+
       const constructorName = plugin.__expression
         ? `(${plugin.__expression})`
         : plugin.name;
 
-      const config = init(this.get('plugin'), this.get('args'));
+      const config = init(plugin, args);
 
       Object.defineProperties(config, {
         __pluginName: { value: this.name },
-        __pluginArgs: { value: this.get('args') },
+        __pluginArgs: { value: args },
         __pluginConstructorName: { value: constructorName },
+        __pluginPath: { value: pluginPath },
       });
 
       return config;

test/Config.js

@@ -1,5 +1,7 @@
 import test from 'ava';
 import { validate } from 'webpack';
+import EnvironmentPlugin from 'webpack/lib/EnvironmentPlugin';
+import stringify from 'javascript-stringify';
 import Config from '../src/Config';
 
 class StringifyPlugin {
@@ -100,6 +102,9 @@ test('toConfig with values', t => {
     .plugin('stringify')
     .use(StringifyPlugin)
     .end()
+    .plugin('env')
+    .use(require.resolve('webpack/lib/EnvironmentPlugin'))
+    .end()
     .module.defaultRule('inline')
     .use('banner')
     .loader('banner-loader')
@@ -132,7 +137,7 @@ test('toConfig with values', t => {
       path: 'build',
     },
     target: 'node',
-    plugins: [new StringifyPlugin()],
+    plugins: [new StringifyPlugin(), new EnvironmentPlugin()],
     module: {
       defaultRules: [
         {
@@ -199,6 +204,9 @@ test('validate with values', t => {
     .plugin('stringify')
     .use(StringifyPlugin)
     .end()
+    .plugin('env')
+    .use(require.resolve('webpack/lib/EnvironmentPlugin'), [{ VAR: false }])
+    .end()
     .module.rule('compile')
     .include.add('alpha')
     .add('beta')
@@ -228,10 +236,16 @@ test('toString', t => {
     .use('babel')
     .loader('babel-loader');
 
+  const envPluginPath = require.resolve('webpack/lib/EnvironmentPlugin');
+  const stringifiedEnvPluginPath = stringify(envPluginPath);
+
   class FooPlugin {}
   FooPlugin.__expression = `require('foo-plugin')`;
 
   config
+    .plugin('env')
+    .use(envPluginPath, [{ VAR: false }])
+    .end()
     .plugin('gamma')
     .use(FooPlugin)
     .end()
@@ -264,6 +278,12 @@ test('toString', t => {
     ]
   },
   plugins: [
+    /* config.plugin('env') */
+    new (require(${stringifiedEnvPluginPath}))(
+      {
+        VAR: false
+      }
+    ),
     /* config.plugin('gamma') */
     new (require('foo-plugin'))(),
     /* config.plugin('delta') */

test/Plugin.js

@@ -1,4 +1,5 @@
 import test from 'ava';
+import EnvironmentPlugin from 'webpack/lib/EnvironmentPlugin';
 import Plugin from '../src/Plugin';
 
 class StringifyPlugin {
@@ -97,3 +98,16 @@ test('toConfig with object literal plugin', t => {
 
   t.is(initialized, TestPlugin);
 });
+
+test('toConfig with plugin as path', t => {
+  const plugin = new Plugin(null, 'gamma');
+  const envPluginPath = require.resolve('webpack/lib/EnvironmentPlugin');
+
+  plugin.use(envPluginPath);
+
+  const initialized = plugin.toConfig();
+
+  t.true(initialized instanceof EnvironmentPlugin);
+  t.is(initialized.__pluginConstructorName, 'EnvironmentPlugin');
+  t.is(initialized.__pluginPath, envPluginPath);
+});