Implement modular compilation

bin/dartdevc.dart

 #!/usr/bin/env dart
-// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// 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.
 
-/// Runs dev_compiler's checker, and optionally the code generator.
-/// Also can run a server for local development.
-library dev_compiler.bin.dartdevc;
+/// Command line entry point for Dart Development Compiler (dartdevc).
+///
+/// Supported commands are
+///   * compile: builds a collection of dart libraries into a single JS module
+///
+/// Additionally, these commands are being considered
+///   * link:  combines several JS modules into a single JS file
+///   * build: compiles & links a set of code, automatically determining
+///            appropriate groupings of libraries to combine into JS modules
+///   * watch: watch a directory and recompile build units automatically
+///   * serve: uses `watch` to recompile and exposes a simple static file server
+///            for local development
+///
+/// These commands are combined so we have less names to expose on the PATH,
+/// and for development simplicity while the precise UI has not been determined.
+///
+/// A more typical structure for web tools is simply to have the compiler with
+/// "watch" as an option. The challenge for us is:
+///
+/// * Dart used to assume whole-program compiles, so we don't have a
+///   user-declared unit of building, and neither "libraries" or "packages" will
+///   work,
+/// * We do not assume a `node` JS installation, so we cannot easily reuse
+///   existing tools for the "link" step, or assume users have a local
+///   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:dev_compiler/src/compiler/command.dart';
 
-import 'package:dev_compiler/devc.dart' show devCompilerVersion;
-import 'package:dev_compiler/src/compiler.dart'
-    show validateOptions, compile, setupLogger;
-import 'package:dev_compiler/src/options.dart';
-
-const String _appName = 'dartdevc';
-
-void _showUsageAndExit() {
-  print('usage: dartdevc [<options>] <file.dart>...\n');
-  print('<file.dart> is one or more Dart files to process.\n');
-  print('<options> include:\n');
-  print(argParser.usage);
-  exit(1);
+main(List<String> args) async {
+  var runner = new CommandRunner('dartdevc', 'Dart Development Compiler');
+  runner.addCommand(new CompileCommand());
+  try {
+    await runner.run(args);
+  } on UsageException catch (e) {
+    // Incorrect usage, input file not found, etc.
+    print(e);
+    exit(64);
+  } on CompileErrorException catch (e) {
+    // Code has error(s) and failed to compile.
+    print(e);
+    exit(1);
+  } catch (e, s) {
+    // 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).
+    //
+    print("");
+    print("We're sorry, you've found a bug in our compiler.");
+    print("You can report this bug at:");
+    print("    https://github.com/dart-lang/dev_compiler/issues");
+    print("");
+    print("Please include the information below in your report, along with");
+    print("any other information that may help us track it down. Thanks!");
+    print("");
+    print("    dartdevc arguments: " + args.join(' '));
+    print("    dart --version: ${Platform.version}");
+    print("");
+    print("```");
+    print(e);
+    print(s);
+    print("```");
+  }
 }
-
-main(List<String> args) {
-  var options;
-
-  try {
-    options = validateOptions(args);
-  } on FormatException catch (e) {
-    print('${e.message}\n');
-    _showUsageAndExit();
-  }
-
-  if (options == null || options.help) _showUsageAndExit();
-  if (options.version) {
-    print('${_appName} version ${devCompilerVersion}');
-    exit(0);
-  }
-
-  setupLogger(options.logLevel, print);
-  bool success = compile(options);
-  exit(success ? 0 : 1);
-}