fix super-niche resolution bug affecting online demo

src/Module.js

@@ -281,7 +281,10 @@ export default class Module {
 	}
 
 	basename () {
-		return makeLegalIdentifier( basename( this.id ).slice( 0, -extname( this.id ).length ) );
+		const base = basename( this.id );
+		const ext = extname( this.id );
+
+		return makeLegalIdentifier( ext ? base.slice( 0, -ext.length ) : base );
 	}
 
 	bindAliases () {

test/function/export-default-anonymous-function/_config.js

@@ -0,0 +1,15 @@
+var fs = require( 'fs' );
+var path = require( 'path' );
+
+module.exports = {
+	description: 'exports an anonymous function with custom ID resolver', // yeah, this is a real edge case
+	options: {
+		resolveId: function ( importee, importer ) {
+			return path.basename( importee ).replace( /\..+/, '' );
+		},
+		load: function ( id ) {
+			console.log( 'id', id )
+			return fs.readFileSync( path.join( __dirname, id + '.js' ), 'utf-8' );
+		}
+	}
+};

test/function/export-default-anonymous-function/answer.js

@@ -0,0 +1 @@
+export default 42;

test/function/export-default-anonymous-function/main.js

@@ -0,0 +1,5 @@
+import answer from './answer';
+
+export default function () {
+	console.log( 'the answer is ' + answer );
+}