Move all args to per-request for the worker, and add a test

bin/dartdevc.dart

 #!/usr/bin/env dart
 // Copyright (c) 2016, 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.
 
 /// Command line entry point for Dart Development Compiler (dartdevc).
 ///
 /// Supported commands are
 ///   * compile: builds a collection of dart libraries into a single JS module
 ///
@@ skipping 19 matching lines @@
 ///   file server,
 /// * We didn't have a file watcher API at first,
 /// * We had no conventions about where compiled output should go (or even
 ///   that we would be compiling at all, vs running on an in-browser Dart VM),
 /// * We wanted a good first impression with our simple examples, so we used
 ///   local file servers, and users have an expectation of it now, even though
 ///   it doesn't scale to typical apps that need their own real servers.
 
 import 'dart:io';
 import 'package:args/command_runner.dart';
+import 'package:bazel_worker/bazel_worker.dart';
 import 'package:dev_compiler/src/compiler/command.dart';
 
 main(List<String> args) async {
+  // Always returns a new modifiable list.
   args = _preprocessArgs(args);
 
-  var runner = new CommandRunner('dartdevc', 'Dart Development Compiler');
-  runner.addCommand(new CompileCommand());
-  try {
-    await runner.run(args);
-  } catch (e, s) {
-    exit(handleError(e, s, args));
+  if (args.contains('--persistent_worker')) {
+    new _CompilerWorker(args..remove('--persistent_worker')).run();
+  } else {
+    exitCode = _runCommand(args);
   }
 }
 
+/// Runs a single compile command, and returns an exit code.
+int _runCommand(List<String> args, {MessageHandler messageHandler}) {
+  try {
+    var runner = new CommandRunner('dartdevc', 'Dart Development Compiler');
+    runner.addCommand(new CompileCommand(messageHandler: messageHandler));
+    runner.run(args);
+  } catch (e, s) {
+    return _handleError(e, s, args, messageHandler: messageHandler);
+  }
+  return EXIT_CODE_OK;
+}
+
+/// Runs the compiler worker loop.
+class _CompilerWorker extends SyncWorkerLoop {
+  /// The original args supplied to the executable.
+  final List<String> _startupArgs;
+
+  _CompilerWorker(this._startupArgs) : super();
+
+  /// Performs each individual work request.
+  WorkResponse performRequest(WorkRequest request) {
+    var args = new List.from(_startupArgs)..addAll(request.arguments);
+
+    var output = new StringBuffer();
+    return new WorkResponse()
+      ..exitCode = _runCommand(args, messageHandler: output.writeln)
+      ..output = output.toString();
+  }
+}
+
+/// Handles [error] in a uniform fashion. Returns the proper exit code and calls
+/// [messageHandler] with messages.
+int _handleError(dynamic error, dynamic stackTrace, List<String> args,
+    {MessageHandler messageHandler}) {
+  messageHandler ??= print;
+
+  if (error is UsageException) {
+    // Incorrect usage, input file not found, etc.
+    messageHandler(error);
+    return 64;
+  } else if (error is CompileErrorException) {
+    // Code has error(s) and failed to compile.
+    messageHandler(error);
+    return 1;
+  } else {
+    // Anything else is likely a compiler bug.
+    //
+    // --unsafe-force-compile is a bit of a grey area, but it's nice not to
+    // crash while compiling
+    // (of course, output code may crash, if it had errors).
+    //
+    messageHandler("");
+    messageHandler("We're sorry, you've found a bug in our compiler.");
+    messageHandler("You can report this bug at:");
+    messageHandler("    https://github.com/dart-lang/dev_compiler/issues");
+    messageHandler("");
+    messageHandler(
+        "Please include the information below in your report, along with");
+    messageHandler(
+        "any other information that may help us track it down. Thanks!");
+    messageHandler("");
+    messageHandler("    dartdevc arguments: " + args.join(' '));
+    messageHandler("    dart --version: ${Platform.version}");
+    messageHandler("");
+    messageHandler("```");
+    messageHandler(error);
+    messageHandler(stackTrace);
+    messageHandler("```");
+    return 70;
+  }
+}
+
+/// Always returns a new modifiable list.
+///
 /// If the final arg is `@file_path` then read in all the lines of that file
 /// and add those as args.
 ///
 /// Bazel actions that support workers must provide all their per-WorkRequest
 /// arguments in a file like this instead of as normal args.
 List<String> _preprocessArgs(List<String> args) {
+  args = new List.from(args);
   if (args.isNotEmpty && args.last.startsWith('@')) {
-    return new List.from(args)
-      ..addAll(new File(args.last.substring(1)).readAsLinesSync());
-  } else {
-    return args;
+    var fileArg = args.removeLast();
+    args.addAll(new File(fileArg.substring(1)).readAsLinesSync());
   }
+  return args;
 }