fix missing namespace member warnings (closes #1045)

src/ast/nodes/MemberExpression.js

@@ -1,3 +1,5 @@
+import getLocation from '../../utils/getLocation.js';
+import relativeId from '../../utils/relativeId.js';
 import isReference from '../utils/isReference.js';
 import Node from '../Node.js';
 import { UNKNOWN } from '../values.js';
@@ -26,12 +28,16 @@ export default class MemberExpression extends Node {
 			let declaration = scope.findDeclaration( keypath.root.name );
 
 			while ( declaration.isNamespace && keypath.parts.length ) {
+				const exporterId = declaration.module.id;
+
 				const part = keypath.parts[0];
 				declaration = declaration.module.traceExport( part.name );
 
 				if ( !declaration ) {
-					this.module.bundle.onwarn( `Export '${part.name}' is not defined by '${this.module.id}'` );
-					break;
+					const { line, column } = getLocation( this.module.code, this.start );
+					this.module.bundle.onwarn( `${relativeId( this.module.id )} (${line}:${column}) '${part.name}' is not exported by '${relativeId( exporterId )}'. See https://github.com/rollup/rollup/wiki/Troubleshooting#name-is-not-exported-by-module` );
+					this.replacement = 'undefined';
+					return;
 				}
 
 				keypath.parts.shift();
@@ -64,6 +70,10 @@ export default class MemberExpression extends Node {
 			if ( name !== this.name ) code.overwrite( this.start, this.end, name, true );
 		}
 
+		else if ( this.replacement ) {
+			code.overwrite( this.start, this.end, this.replacement, true );
+		}
+
 		super.render( code, es );
 	}
 

test/function/namespace-missing-export/_config.js

@@ -3,7 +3,7 @@ var assert = require( 'assert' );
 module.exports = {
 	options: {
 		onwarn: function ( msg ) {
-			assert.ok( /Export 'foo' is not defined by/.test( msg ) );
+			assert.equal( msg, `main.js (3:21) 'foo' is not exported by 'empty.js'. See https://github.com/rollup/rollup/wiki/Troubleshooting#name-is-not-exported-by-module` );
 		}
 	}
 };