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

bin/dartdevc.dart

Index: bin/dartdevc.dart
diff --git a/bin/dartdevc.dart b/bin/dartdevc.dart
index 0ee480ac83faca90afbbc6f5ab5cc0e827c6ac7f..1942b7e8556b60a558b5b279b092da2989ed3fac 100755
--- a/bin/dartdevc.dart
+++ b/bin/dartdevc.dart
@@ -37,30 +37,104 @@
 
 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());
+  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 {
-    await runner.run(args);
+    var runner = new CommandRunner('dartdevc', 'Dart Development Compiler');
+    runner.addCommand(new CompileCommand(messageHandler: messageHandler));
+    runner.run(args);
   } catch (e, s) {
-    exit(handleError(e, s, args));
+    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;
 }