error for extra args, print red errors

webdev/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.2.1
+
+- Exit with an error if unsupported arguments are passed to `build` command.
+
 ## 0.2.0
 
 - Pass the arguments supporting `directory:port` for the `serve` command.

webdev/bin/webdev.dart

@@ -15,19 +15,19 @@ Future main(List<String> args) async {
   try {
     exitCode = await run(args);
   } on UsageException catch (e) {
-    print(yellow.wrap(e.message));
+    print(red.wrap(e.message));
     print(' ');
     print(e.usage);
     exitCode = ExitCode.usage.code;
   } on FileSystemException catch (e) {
-    print(yellow.wrap('$_boldApp could not run in the current directory.'));
+    print(red.wrap('$_boldApp could not run in the current directory.'));
     print(e.message);
     if (e.path != null) {
       print('  ${e.path}');
     }
     exitCode = ExitCode.config.code;
   } on PackageException catch (e) {
-    print(yellow.wrap('$_boldApp could not run for this project.'));
+    print(red.wrap('$_boldApp could not run for this project.'));
     for (var detail in e.details) {
       print(yellow.wrap(detail.error));
       if (detail.description != null) {

webdev/lib/src/command/build_command.dart

@@ -3,6 +3,9 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
+
+import 'package:args/command_runner.dart';
+
 import 'command_base.dart';
 
 /// Command to execute pub run build_runner build.
@@ -16,5 +19,13 @@ class BuildCommand extends CommandBase {
   final description = 'Run builders to build a package.';
 
   @override
-  Future<int> run() => runCore('build');
+  Future<int> run() {
+    if (argResults.rest.isNotEmpty) {
+      throw new UsageException(
+          'Arguments were provided that are not supported: '
+          '"${argResults.rest.join(' ')}".',
+          argParser.usage);
+    }
+    return runCore('build');
+  }
 }

webdev/pubspec.yaml

@@ -1,5 +1,5 @@
 name: webdev
-version: 0.2.0
+version: 0.2.1-dev
 author: Dart Team <misc@dartlang.org>
 homepage: https://github.com/dart-lang/webdev
 description: >-

webdev/test/integration_test.dart

@@ -19,6 +19,15 @@ void main() {
     await process.shouldExit(64);
   });
 
+  test('passing extra args to build fails with bad usage', () async {
+    var process = await runWebDev(['build', 'extra', 'args']);
+
+    await expectLater(process.stdout,
+        emits('Arguments were provided that are not supported: "extra args".'));
+
+    await process.shouldExit(64);
+  });
+
   var invalidRanges = <String, List<String>>{
     'build_runner': ['0.7.13+1', '0.9.0'],
     'build_web_compilers': ['0.3.5', '0.4.0']