Added dedupe option to prevent bundling the same package multiple times

Author: Artem Butusov

README.md

@@ -65,6 +65,11 @@ export default {
       // ES2015 modules
       modulesOnly: true, // Default: false
 
+      // Force resolving for these modules to root's node_modules that helps
+      // to prevent bundling the same package multiple times if package is
+      // imported from dependencies.
+      dedupe: [ 'react', 'react-dom' ], // Default: []
+
       // Any additional options that should be passed through
       // to node-resolve
       customResolveOptions: {

src/index.js

@@ -1,4 +1,4 @@
-import {dirname, extname, normalize, resolve, sep} from 'path';
+import {dirname, extname, normalize, resolve, sep, join} from 'path';
 import builtins from 'builtin-modules';
 import resolveId from 'resolve';
 import isModule from 'is-module';
@@ -40,6 +40,7 @@ function cachedIsFile (file, cb) {
 const resolveIdAsync = (file, opts) => new Promise((fulfil, reject) => resolveId(file, opts, (err, contents) => err ? reject(err) : fulfil(contents)));
 
 export default function nodeResolve ( options = {} ) {
+	const dedupe = options.dedupe || [];
 	const useModule = options.module !== false;
 	const useMain = options.main !== false;
 	const useJsnext = options.jsnext === true;
@@ -82,6 +83,10 @@ export default function nodeResolve ( options = {} ) {
 
 			const basedir = importer ? dirname( importer ) : process.cwd();
 
+			if (dedupe.indexOf(importee) !== -1) {
+				importee = join(process.cwd(), 'node_modules', importee);
+			}
+
 			// https://github.com/defunctzombie/package-browser-field-spec
 			if (options.browser && browserMapCache[importer]) {
 				const resolvedImportee = resolve( basedir, importee );

test/node_modules/react-consumer/index.js

@@ -0,0 +1,4 @@
+import React from 'react'
+import ReactConsumer from 'react-consumer'
+
+export { React, ReactConsumer }

test/node_modules/react/index.js

@@ -761,4 +761,34 @@ describe( 'rollup-plugin-node-resolve', function () {
 		});
 	});
 
+	it( 'single module version is bundle if dedupe is set', () => {
+		return rollup.rollup({
+			input: 'samples/react-app/main.js',
+			plugins: [
+				nodeResolve({
+					dedupe: [ 'react' ]
+				})
+			]
+		}).then( executeBundle ).then( module => {
+			assert.deepEqual(module.exports, { 
+				React: 'react:root',
+				ReactConsumer: 'react-consumer:react:root'
+			});
+		});
+	});
+
+	it( 'multiple module versions are bundled if dedupe is not set', () => {
+		return rollup.rollup({
+			input: 'samples/react-app/main.js',
+			plugins: [
+				nodeResolve()
+			]
+		}).then( executeBundle ).then( module => {
+			assert.deepEqual(module.exports, { 
+				React: 'react:root',
+				ReactConsumer: 'react-consumer:react:child'
+			});
+		});
+	});
+
 });