fixes #610, incorrect help output

lib/src/compiler/command.dart

Index: lib/src/compiler/command.dart
diff --git a/lib/src/compiler/command.dart b/lib/src/compiler/command.dart
index 545d1a4850ad19c930dca6b3ac9e67219b025c72..acf26675d156a24f6e46bd37d10a9774729a0372 100644
--- a/lib/src/compiler/command.dart
+++ b/lib/src/compiler/command.dart
@@ -4,116 +4,169 @@
 
 import 'dart:convert' show JSON;
 import 'dart:io';
-import 'package:args/command_runner.dart';
 import 'package:analyzer/src/generated/source.dart' show Source;
 import 'package:analyzer/src/summary/package_bundle_reader.dart'
     show InSummarySource;
+import 'package:args/args.dart' show ArgParser, ArgResults;
+import 'package:args/command_runner.dart' show UsageException;
+import 'package:path/path.dart' as path;
+
 import 'compiler.dart'
     show BuildUnit, CompilerOptions, JSModuleFile, ModuleCompiler;
 import '../analyzer/context.dart' show AnalyzerOptions;
-import 'package:path/path.dart' as path;
 
-typedef void MessageHandler(Object message);
-
-/// The command for invoking the modular compiler.
-class CompileCommand extends Command {
-  final MessageHandler messageHandler;
-  CompilerOptions _compilerOptions;
-
-  CompileCommand({MessageHandler messageHandler})
-      : this.messageHandler = messageHandler ?? print {
-    argParser.addOption('out', abbr: 'o', help: 'Output file (required)');
-    argParser.addOption('module-root',
-        help: 'Root module directory. '
-            'Generated module paths are relative to this root.');
-    argParser.addOption('library-root',
-        help: 'Root of source files. '
-            'Generated library names are relative to this root.');
-    argParser.addOption('build-root',
-        help: 'Deprecated in favor of --library-root');
-    CompilerOptions.addArguments(argParser);
-    AnalyzerOptions.addArguments(argParser);
+final ArgParser _argParser = () {
+  var argParser = new ArgParser()
+    ..addFlag('help', abbr: 'h', help: 'Display this message.')
+    ..addOption('out', abbr: 'o', help: 'Output file (required).')
+    ..addOption('module-root',
+        help: 'Root module directory.\n'
+            'Generated module paths are relative to this root.')
+    ..addOption('library-root',
+        help: 'Root of source files.\n'
+            'Generated library names are relative to this root.')
+    ..addOption('build-root',
+        help: 'Deprecated in favor of --library-root', hide: true);
+  AnalyzerOptions.addArguments(argParser);
+  CompilerOptions.addArguments(argParser);
+  return argParser;
+}();
+
+/// Runs a single compile for dartdevc.
+///
+/// This handles argument parsing, usage, error handling.
+/// See bin/dartdevc.dart for the actual entry point, which includes Bazel
+/// worker support.
+int compile(List<String> args, {void printFn(Object obj)}) {
+  printFn ??= print;
+  ArgResults argResults;
+  try {
+    argResults = _argParser.parse(args);
+  } on FormatException catch (error) {
+    printFn('$error\n\n$_usageMessage');
+    return 64;
   }
+  try {
+    _compile(argResults, printFn);
+    return 0;
+  } on UsageException catch (error) {
+    // Incorrect usage, input file not found, etc.
+    printFn(error);
+    return 64;
+  } on CompileErrorException catch (error) {
+    // Code has error(s) and failed to compile.
+    printFn(error);
+    return 1;
+  } catch (error, stackTrace) {
+    // 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).
+    //
+    printFn('''
+We're sorry, you've found a bug in our compiler.
+You can report this bug at:
+    https://github.com/dart-lang/dev_compiler/issues
+Please include the information below in your report, along with
+any other information that may help us track it down. Thanks!
+    dartdevc arguments: ${args.join(' ')}
+    dart --version: ${Platform.version}
+```
+$error
+$stackTrace
+```''');
+    return 70;
+  }
+}
 
-  get name => 'compile';
-  get description => 'Compile a set of Dart files into a JavaScript module.';
-
-  @override
-  void run() {
-    var compiler =
-        new ModuleCompiler(new AnalyzerOptions.fromArguments(argResults));
-    _compilerOptions = new CompilerOptions.fromArguments(argResults);
-    var outPath = argResults['out'];
+void _compile(ArgResults argResults, void printFn(Object obj)) {
+  var compiler =
+      new ModuleCompiler(new AnalyzerOptions.fromArguments(argResults));
+  var compilerOpts = new CompilerOptions.fromArguments(argResults);
+  if (argResults['help']) {
+    printFn(_usageMessage);
+    return;
+  }
+  var outPath = argResults['out'];
 
-    if (outPath == null) {
-      usageException('Please include the output file location. For example:\n'
-          '    -o PATH/TO/OUTPUT_FILE.js');
-    }
+  if (outPath == null) {
+    _usageException('Please include the output file location. For example:\n'
+        '    -o PATH/TO/OUTPUT_FILE.js');
+  }
 
-    var libraryRoot = argResults['library-root'] as String;
-    libraryRoot ??= argResults['build-root'] as String;
-    if (libraryRoot != null) {
-      libraryRoot = path.absolute(libraryRoot);
-    } else {
-      libraryRoot = Directory.current.path;
-    }
-    var moduleRoot = argResults['module-root'] as String;
-    String modulePath;
-    if (moduleRoot != null) {
-      moduleRoot = path.absolute(moduleRoot);
-      if (!path.isWithin(moduleRoot, outPath)) {
-        usageException('Output file $outPath must be within the module root '
-            'directory $moduleRoot');
-      }
-      modulePath =
-          path.withoutExtension(path.relative(outPath, from: moduleRoot));
-    } else {
-      moduleRoot = path.dirname(outPath);
-      modulePath = path.basenameWithoutExtension(outPath);
+  var libraryRoot = argResults['library-root'] as String;
+  libraryRoot ??= argResults['build-root'] as String;
+  if (libraryRoot != null) {
+    libraryRoot = path.absolute(libraryRoot);
+  } else {
+    libraryRoot = Directory.current.path;
+  }
+  var moduleRoot = argResults['module-root'] as String;
+  String modulePath;
+  if (moduleRoot != null) {
+    moduleRoot = path.absolute(moduleRoot);
+    if (!path.isWithin(moduleRoot, outPath)) {
+      _usageException('Output file $outPath must be within the module root '
+          'directory $moduleRoot');
     }
+    modulePath =
+        path.withoutExtension(path.relative(outPath, from: moduleRoot));
+  } else {
+    moduleRoot = path.dirname(outPath);
+    modulePath = path.basenameWithoutExtension(outPath);
+  }
 
-    var unit = new BuildUnit(modulePath, libraryRoot, argResults.rest,
-        (source) => _moduleForLibrary(moduleRoot, source));
+  var unit = new BuildUnit(modulePath, libraryRoot, argResults.rest,
+      (source) => _moduleForLibrary(moduleRoot, source, compilerOpts));
 
-    JSModuleFile module = compiler.compile(unit, _compilerOptions);
-    module.errors.forEach(messageHandler);
+  JSModuleFile module = compiler.compile(unit, compilerOpts);
+  module.errors.forEach(printFn);
 
-    if (!module.isValid) throw new CompileErrorException();
+  if (!module.isValid) throw new CompileErrorException();
 
-    // Write JS file, as well as source map and summary (if requested).
-    new File(outPath).writeAsStringSync(module.code);
-    if (module.sourceMap != null) {
-      var mapPath = outPath + '.map';
-      new File(mapPath)
-          .writeAsStringSync(JSON.encode(module.placeSourceMap(mapPath)));
-    }
-    if (module.summaryBytes != null) {
-      var summaryPath = path.withoutExtension(outPath) +
-          '.${_compilerOptions.summaryExtension}';
-      new File(summaryPath).writeAsBytesSync(module.summaryBytes);
-    }
+  // Write JS file, as well as source map and summary (if requested).
+  new File(outPath).writeAsStringSync(module.code);
+  if (module.sourceMap != null) {
+    var mapPath = outPath + '.map';
+    new File(mapPath)
+        .writeAsStringSync(JSON.encode(module.placeSourceMap(mapPath)));
+  }
+  if (module.summaryBytes != null) {
+    var summaryPath =
+        path.withoutExtension(outPath) + '.${compilerOpts.summaryExtension}';
+    new File(summaryPath).writeAsBytesSync(module.summaryBytes);
   }
+}
 
-  String _moduleForLibrary(String moduleRoot, Source source) {
-    if (source is InSummarySource) {
-      var summaryPath = source.summaryPath;
-      var ext = '.${_compilerOptions.summaryExtension}';
-      if (path.isWithin(moduleRoot, summaryPath) && summaryPath.endsWith(ext)) {
-        var buildUnitPath =
-            summaryPath.substring(0, summaryPath.length - ext.length);
-        return path.relative(buildUnitPath, from: moduleRoot);
-      }
-
-      throw usageException(
-          'Imported file ${source.uri} is not within the module root '
-          'directory $moduleRoot');
+String _moduleForLibrary(
+    String moduleRoot, Source source, CompilerOptions compilerOpts) {
+  if (source is InSummarySource) {
+    var summaryPath = source.summaryPath;
+    var ext = '.${compilerOpts.summaryExtension}';
+    if (path.isWithin(moduleRoot, summaryPath) && summaryPath.endsWith(ext)) {
+      var buildUnitPath =
+          summaryPath.substring(0, summaryPath.length - ext.length);
+      return path.relative(buildUnitPath, from: moduleRoot);
     }
 
-    throw usageException(
-        'Imported file "${source.uri}" was not found as a summary or source '
-        'file. Please pass in either the summary or the source file '
-        'for this import.');
+    _usageException('Imported file ${source.uri} is not within the module root '
+        'directory $moduleRoot');
   }
+
+  _usageException(
+      'Imported file "${source.uri}" was not found as a summary or source '
+      'file. Please pass in either the summary or the source file '
+      'for this import.');
+  return null; // unreachable
+}
+
+final _usageMessage =
+    'Dart Development Compiler compiles Dart into a JavaScript module.'
+    '\n\n${_argParser.usage}';
+
+void _usageException(String message) {
+  throw new UsageException(message, _usageMessage);
 }
 
 /// Thrown when the input source code has errors.