Implement modular compilation

lib/src/multi_package_resolver.dart

-// Copyright (c) 2014, 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.
-
-import 'dart:io';
-
-import 'package:analyzer/src/generated/java_io.dart';
-import 'package:analyzer/src/generated/source.dart';
-import 'package:analyzer/src/generated/source_io.dart';
-import 'package:path/path.dart' show join;
-
-/// A package resolver that supports a non-standard package layout, where
-/// packages with dotted names are expanded to a hierarchy of directories, and
-/// packages can be found on one or more locations.
-class MultiPackageResolver extends UriResolver {
-  final List<String> searchPaths;
-  MultiPackageResolver(this.searchPaths);
-
-  @override
-  Source resolveAbsolute(Uri uri, [Uri actualUri]) {
-    var candidates = _expandPath(uri);
-    if (candidates == null) return null;
-
-    for (var path in candidates) {
-      var resolvedPath = _resolve(path);
-      if (resolvedPath != null) {
-        return new FileBasedSource(
-            new JavaFile(resolvedPath), actualUri != null ? actualUri : uri);
-      }
-    }
-    return null;
-  }
-
-  /// Resolve [path] by looking at each prefix in [searchPaths] and returning
-  /// the first location where `prefix + path` exists.
-  String _resolve(String path) {
-    for (var prefix in searchPaths) {
-      var resolvedPath = join(prefix, path);
-      if (new File(resolvedPath).existsSync()) return resolvedPath;
-    }
-    return null;
-  }
-
-  /// Expand `uri.path`, replacing dots in the package name with slashes.
-  List<String> _expandPath(Uri uri) {
-    if (uri.scheme != 'package') return null;
-    var path = uri.path;
-    var slashPos = path.indexOf('/');
-    var packagePath = path.substring(0, slashPos).replaceAll(".", "/");
-    var filePath = path.substring(slashPos + 1);
-    return ['$packagePath/lib/$filePath', '$packagePath/$filePath'];
-  }
-}