warn on missing options in config file

bin/handleError.js

@@ -1,6 +1,10 @@
 var chalk = require( 'chalk' );
 
 var handlers = {
+	MISSING_CONFIG: function () {
+		console.error( chalk.red( 'Config file must export an options object. See https://github.com/rollup/rollup/wiki/Command-Line-Interface#using-a-config-file' ) );
+	},
+
 	MISSING_INPUT_OPTION: function () {
 		console.error( chalk.red( 'You must specify an --input (-i) option' ) );
 	},

bin/runRollup.js

@@ -59,6 +59,9 @@ module.exports = function ( command ) {
 
 			try {
 				var options = require( path.resolve( config ) );
+				if ( Object.keys( options ).length === 0 ) {
+					handleError({ code: 'MISSING_CONFIG' });
+				}
 			} catch ( err ) {
 				handleError( err );
 			}

test/cli/config-missing-export/_config.js

@@ -0,0 +1,9 @@
+var assert = require( 'assert' );
+
+module.exports = {
+	description: 'throws error if config does not export an object',
+	command: 'rollup -c',
+	error: function ( err ) {
+		assert.ok( /Config file must export an options object/.test( err.message ) );
+	}
+};

test/test.js

@@ -342,7 +342,10 @@ describe( 'rollup', function () {
 							PATH: path.resolve( __dirname, '../bin' ) + path.delimiter + process.env.PATH
 						}
 					}, function ( err, code, stderr ) {
-						if ( err ) return done( err );
+						if ( err || config.error ) {
+							config.error( err );
+							return done();
+						}
 
 						if ( stderr ) console.error( stderr );