Fail on duplicating in export * from

src/Bundle.js

@@ -210,7 +210,24 @@ export default class Bundle {
 				this.modules.push( module );
 				this.moduleById.set( id, module );
 
-				return this.fetchAllDependencies( module ).then( () => module );
+				return this.fetchAllDependencies( module ).then( () => {
+					module.exportsAll = blank();
+					keys( module.exports ).forEach( name => {
+						module.exportsAll[name] = module.id;
+					});
+					module.exportAllSources.forEach( source => {
+						const id = module.resolvedIds[ source ];
+						const exportAllModule = this.moduleById.get( id );
+						keys( exportAllModule.exportsAll ).forEach( name => {
+							if ( name in module.exportsAll ) {
+								throw new Error( `A module cannot have multiple exports with the same name ('${name}')` +
+									` from ${module.exportsAll[ name ] } and ${exportAllModule.exportsAll[ name ]}` );
+							}
+							module.exportsAll[ name ] = exportAllModule.exportsAll[ name ];
+						});
+					});
+					return module;
+				});
 			});
 	}
 

src/utils/object.js

@@ -1,3 +1,4 @@
+const { hasOwnProperty } = Object.prototype;
 export const { keys } = Object;
 
 export function blank () {
@@ -11,7 +12,7 @@ export function forOwn ( object, func ) {
 export function assign ( target, ...sources ) {
 	sources.forEach( source => {
 		for ( let key in source ) {
-			if ( source.hasOwnProperty( key ) ) target[ key ] = source[ key ];
+			if ( hasOwnProperty.call( source, key ) ) target[ key ] = source[ key ];
 		}
 	});
 

test/function/double-named-export-from/_config.js

@@ -0,0 +1,14 @@
+const path = require('path');
+const assert = require( 'assert' );
+
+function normalize( file ) {
+	return path.resolve( __dirname, file ).split( '\\' ).join( '/' );
+}
+
+module.exports = {
+	description: 'throws on duplicate export * from',
+	error: err => {
+		assert.equal( err.message, `A module cannot have multiple exports with the same name ('foo')` +
+			` from ${normalize( 'foo.js' )} and ${normalize( 'deep.js' )}` );
+	}
+};

test/function/double-named-export-from/bar.js

@@ -0,0 +1 @@
+export * from './deep.js';

test/function/double-named-export-from/deep.js

@@ -0,0 +1 @@
+export var foo = 2;

test/function/double-named-export-from/foo.js

@@ -0,0 +1 @@
+export var foo = 1;

test/function/double-named-export-from/main.js

@@ -0,0 +1,2 @@
+export * from './foo.js';
+export * from './bar.js';