Fix the output when running dart help pub. Process.runSync(..) is used since printUsage() is not an async method.

Bug: https://github.com/dart-lang/sdk/issues/41040
Change-Id: I9e4fbab333bbd67dcab2b1e0752fc0debb80be46
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/139833
Commit-Queue: Jaime Wren <jwren@google.com>
Reviewed-by: Devon Carew <devoncarew@google.com>

pkg/dartdev/lib/src/commands/pub.dart

@@ -15,6 +15,25 @@ class PubCommand extends DartdevCommand<int> {
 
   final ArgParser argParser = ArgParser.allowAnything();
 
+  /// Override [printUsage] for invocations of 'dart help pub' which won't
+  /// execute [run] below.  Without this, the 'dart help pub' reports the
+  /// command pub with no commands or flags.
+  @override
+  void printUsage() {
+    final command = sdk.pub;
+    final args = ['help'];
+
+    log.trace('$command ${args.first}');
+
+    // Call 'pub help'
+    // Process.runSync(..) is used since [printUsage] is not an async method,
+    // and we want to guarantee that the result (the help text for the console)
+    // is printed before command exits.
+    final result = Process.runSync(command, args);
+    stderr.write(result.stderr);
+    stdout.write(result.stdout);
+  }
+
   @override
   FutureOr<int> run() async {
     final command = sdk.pub;

pkg/dartdev/test/commands/help_test.dart

@@ -0,0 +1,26 @@
+// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:test/test.dart';
+
+import '../utils.dart';
+
+void main() {
+  group('help', help);
+}
+
+void help() {
+  TestProject p;
+
+  tearDown(() => p?.dispose());
+
+  test('pub', () {
+    p = project();
+    var result = p.runSync('help', ['pub']);
+
+    var pubHelpResult = p.runSync('pub', ['help']);
+    expect(result.stdout, contains(pubHelpResult.stdout));
+    expect(result.stderr, contains(pubHelpResult.stderr));
+  });
+}

pkg/dartdev/test/test_all.dart

@@ -8,6 +8,7 @@ import 'commands/analyze_test.dart' as analyze;
 import 'commands/create_test.dart' as create;
 import 'commands/flag_test.dart' as flag;
 import 'commands/format_test.dart' as format;
+import 'commands/help_test.dart' as help;
 import 'commands/migrate_test.dart' as migrate;
 import 'commands/pub_test.dart' as pub;
 import 'commands/test_test.dart' as test;
@@ -16,11 +17,12 @@ import 'sdk_test.dart' as sdk;
 import 'utils_test.dart' as utils;
 
 main() {
-  group('dartdev', () {
+  group('dart', () {
     analyze.main();
     create.main();
     flag.main();
     format.main();
+    help.main();
     migrate.main();
     pub.main();
     test.main();