Added dedupe option to prevent bundling the same package multiple times

.gitignore

@@ -3,3 +3,4 @@ node_modules
 dist
 .gobble*
 !test/node_modules
+!test/node_modules/react-consumer/node_modules

README.md

@@ -74,6 +74,11 @@ 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: {

index.d.ts

@@ -70,6 +70,12 @@ interface RollupNodeResolveOptions {
 	 * @default false
 	 */
 	modulesOnly?: boolean;
+	/**
+	 * 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?: string[];
 	/**
 	 * Any additional options that should be passed through
 	 * to node-resolve

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';
@@ -72,6 +72,7 @@ const resolveIdAsync = (file, opts) => new Promise((fulfil, reject) => resolveId
 export default function nodeResolve ( options = {} ) {
 	const mainFields = getMainFields(options);
 	const useBrowserOverrides = mainFields.indexOf('browser') !== -1;
+	const dedupe = options.dedupe || [];
 	const isPreferBuiltinsSet = options.preferBuiltins === true || options.preferBuiltins === false;
 	const preferBuiltins = isPreferBuiltinsSet ? options.preferBuiltins : true;
 	const customResolveOptions = options.customResolveOptions || {};
@@ -107,6 +108,10 @@ 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 (useBrowserOverrides && browserMapCache[importer]) {
 				const resolvedImportee = resolve( basedir, importee );

test/samples/react-app/main.js

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

test/test.js

@@ -777,4 +777,34 @@ 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'
+			});
+		});
+	});
+
 });