no longer require entry points to be specified in the build.dart file

pkg/polymer/lib/builder.dart

 // Copyright (c) 2012, 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.
 
 /// Common logic to make it easy to run the polymer linter and deploy tool.
 ///
 /// The functions in this library are designed to make it easier to create
 /// `build.dart` files. A `build.dart` file is a Dart script that can be invoked
 /// from the command line, but that can also invoked automatically by the Dart
 /// Editor whenever a file in your project changes or when selecting some menu
@@ skipping 65 matching lines @@
 ///
 ///     main(args) {
 ///        build(entryPoints: ['web/index.html'], options: parseOptions(args));
 ///     }
 library polymer.builder;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:args/args.dart';
+import 'package:path/path.dart' as path;
+import 'package:yaml/yaml.dart';
 
 import 'src/build/linter.dart';
 import 'src/build/runner.dart';
 import 'src/build/common.dart';
 
 import 'transformer.dart';
 
 
 /// Runs the polymer linter on any relevant file in your package, such as any
 /// .html file under 'lib/', 'asset/', and 'web/'. And, if requested, creates a
@@ skipping 13 matching lines @@
 /// and the location where to find the code for any package it depends on
 /// ([packageDirs]). This is inferred automatically, but can be overriden if
 /// those arguments are provided.
 Future build({List<String> entryPoints, CommandLineOptions options,
     String currentPackage, Map<String, String> packageDirs}) {
   if (options == null) {
     print('warning: now that main takes arguments, you need to explicitly pass'
         ' options to build(). Running as if no options were passed.');
     options = parseOptions([]);
   }
+  if (entryPoints == null) entryPoints = _parseEntryPointsFromPubspec();
+
   return options.forceDeploy
       ? deploy(entryPoints: entryPoints, options: options,
             currentPackage: currentPackage, packageDirs: packageDirs)
       : lint(entryPoints: entryPoints, options: options,
             currentPackage: currentPackage, packageDirs: packageDirs);
 }
 
 
 /// Runs the polymer linter on any relevant file in your package,
 /// such as any .html file under 'lib/', 'asset/', and 'web/'.
 ///
 /// The [entryPoints] list contains files under web/ that should be treated as
 /// entry points. Each entry on this list is a relative path from the package
 /// root (for example 'web/index.html'). If null, all files under 'web/' are
 /// treated as possible entry points.
 ///
 /// Options must be passed by passing the [options] argument.
 ///
 /// The linter needs to know the name of the [currentPackage] and the location
 /// where to find the code for any package it depends on ([packageDirs]). This
 /// is inferred automatically, but can be overriden by passing the arguments.
 Future lint({List<String> entryPoints, CommandLineOptions options,
     String currentPackage, Map<String, String> packageDirs}) {
   if (options == null) {
     print('warning: now that main takes arguments, you need to explicitly pass'
         ' options to lint(). Running as if no options were passed.');
     options = parseOptions([]);
   }
   if (currentPackage == null) currentPackage = readCurrentPackageFromPubspec();
+  if (entryPoints == null) entryPoints = _parseEntryPointsFromPubspec();
   var linterOptions = new TransformOptions(entryPoints: entryPoints);
   var linter = new Linter(linterOptions);
+
   return runBarback(new BarbackOptions([[linter]], null,
       currentPackage: currentPackage, packageDirs: packageDirs,
       machineFormat: options.machineFormat));
 }
 
 /// Creates a directory suitable for deploying a Polymer application to a
 /// server.
 ///
 /// **Note**: this function will be replaced in the future by the `pub deploy`
 /// command.
@@ skipping 10 matching lines @@
 /// ([packageDirs]). This is inferred automatically, but can be overriden if
 /// those arguments are provided.
 Future deploy({List<String> entryPoints, CommandLineOptions options,
     String currentPackage, Map<String, String> packageDirs}) {
   if (options == null) {
     print('warning: now that main takes arguments, you need to explicitly pass'
         ' options to deploy(). Running as if no options were passed.');
     options = parseOptions([]);
   }
   if (currentPackage == null) currentPackage = readCurrentPackageFromPubspec();
+  if (entryPoints == null) entryPoints = _parseEntryPointsFromPubspec();
 
   var transformOptions = new TransformOptions(
       entryPoints: entryPoints,
       directlyIncludeJS: options.directlyIncludeJS,
       contentSecurityPolicy: options.contentSecurityPolicy,
       releaseMode: options.releaseMode);
 
   var phases = new PolymerTransformerGroup(transformOptions).phases;
   var barbackOptions = new BarbackOptions(
       phases, options.outDir, currentPackage: currentPackage,
@@ skipping 121 matching lines @@
   }
   if (res['help']) {
     print('A build script that invokes the polymer linter and deploy tools.');
     showUsage();
     exit(0);
   }
   return new CommandLineOptions(res['changed'], res['removed'], res['clean'],
       res['full'], res['machine'], res['deploy'], res['out'], res['js'],
       res['csp'], !res['debug']);
 }
+
+List<String> _parseEntryPointsFromPubspec() {
+  var entryPoints = [];
+  var pubspec = new File(path.join(
+      path.dirname(Platform.script.path), 'pubspec.yaml'));
+  if (!pubspec.existsSync()) {
+    print('error: pubspec.yaml file not found.');
+    return null;
+  }
+  var transformers = loadYaml(pubspec.readAsStringSync())['transformers'];
+  if (transformers == null) return null;
+  if (transformers is! List) {
+    print('Unexpected value for transformers, expected a List.');
+    return null;
+  }
+
+  transformers.forEach((t) {
+    if (t is! Map) return;
+    var polymer = t['polymer'];
+    if (polymer == null || polymer is! Map) return;
+
+    var parsedEntryPoints = readEntrypoints(polymer['entry_points']);
+    if (parsedEntryPoints == null) return;
+
+    entryPoints.addAll(parsedEntryPoints);
+  });
+  return entryPoints.isEmpty ? null : entryPoints;
+}