Add package implementation.

lib/src/sync_package_resolver.dart

Index: lib/src/sync_package_resolver.dart
diff --git a/lib/src/sync_package_resolver.dart b/lib/src/sync_package_resolver.dart
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+// 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.
+
+import 'dart:async';
+
+import 'package:http/http.dart' as http;
+
+import 'no_package_resolver.dart';
+import 'package_config_resolver.dart';
+import 'package_resolver.dart';
+import 'package_root_resolver.dart';
+import 'utils.dart';
+
+/// A class that defines how to resolve `package:` URIs.
+///
+/// This includes the information necessary to resolve `package:` URIs using
+/// either a package config or a package root. It can be used both as a standard
+/// cross-package representation of the user's configuration, and as a means of
+/// concretely locating packages and the assets they contain.
+///
+/// Unlike [PackageResolver], all members on this are synchronous, which may
+/// require that more data be loaded up front. This is useful when primarily
+/// dealing with user-created package resolution strategies, whereas
+/// [PackageInfo] is usually preferable when the current Isolate's package
+/// resolution logic may be used.
+///
+/// This class should not be implemented by user code.
+abstract class SyncPackageResolver {
+  /// The map contained in the parsed package config.
+  ///
+  /// This maps package names to the base URIs for those packages. These are
+  /// already resolved relative to [packageConfigUri], so if they're relative
+  /// they should be considered relative to [Uri.base]. They're normalized to
+  /// ensure that all URLs end with a trailing slash.
+  ///
+  /// [urlFor] should generally be used rather than looking up package URLs in
+  /// this map, to ensure that code works with a package root as well as a
+  /// package config.
+  ///
+  /// Returns `null` when using a [packageRoot] for resolution, or when no
+  /// package resolution is being used.
+  Map<String, Uri> get packageConfigMap;
+
+  /// The URI for the package config.
+  ///
+  /// This is the URI from which [packageConfigMap] was parsed, if that's
+  /// available. Otherwise, it's a `data:` URI containing a serialized
+  /// representation of [packageConfigMap]. This `data:` URI should be accepted
+  /// by all Dart tools.
+  ///
+  /// Note that if this is a `data:` URI, it's likely not safe to pass as a
+  /// parameter to a Dart process due to length limits.
+  ///
+  /// Returns `null` when using a [packageRoot] for resolution, or when no
+  /// package resolution is being used.
+  Uri get packageConfigUri;
+
+  /// The base URL for resolving `package:` URLs.
+  ///
+  /// This is normalized so that it always ends with a trailing slash.
+  ///
+  /// Returns `null` when using a [packageConfigMap] for resolution, or when no
+  /// package resolution is being used.
+  Uri get packageRoot;
+
+  /// Returns a wrapper for [this] that implements [PackageResolver].
+  PackageResolver get asAsync;
+
+  /// Returns the argument to pass to a subprocess to get it to use this package
+  /// resolution strategy when resolving `package:` URIs.
+  ///
+  /// This uses the `--package-root` or `--package` flags, which are the
+  /// convention supported by the Dart VM and dart2js.
+  ///
+  /// Note that if [packageConfigUri] is a `data:` URI, it may be too large to
+  /// pass on the command line.
+  ///
+  /// Returns `null` if no package resolution is in use.
+  String get processArgument;
+
+  /// Returns a package resolution strategy describing how the current isolate
+  /// resolves `package:` URIs.
+  ///
+  /// This may throw exceptions if loading or parsing the isolate's package map
+  /// fails.
+  static final Future<SyncPackageResolver> current =
+      PackageResolver.current.asSync;
+
+  /// Returns a package resolution strategy that is unable to resolve any
+  /// `package:` URIs.
+  static final SyncPackageResolver none = new NoPackageResolver();
+
+  /// Loads a package config file from [uri] and returns its package resolution
+  /// strategy.
+  ///
+  /// This supports `file:`, `http:`, `data:` and `package:` URIs. It throws an
+  /// [UnsupportedError] for any other schemes. If [client] is passed and an
+  /// HTTP request is needed, it's used to make that request; otherwise, a
+  /// default client is used.
+  ///
+  /// [uri] may be a [String] or a [Uri].
+  static Future<SyncPackageResolver> loadConfig(uri, {http.Client client})
+      async {
+    uri = asUri(uri, "uri");
+    return new SyncPackageResolver.config(
+        await loadConfigMap(uri, client: client),
+        uri: uri);
+  }
+
+  /// Returns the package resolution strategy for the given [packageConfigMap].
+  ///
+  /// If passed, [uri] specifies the URI from which [packageConfigMap] was
+  /// loaded. It may be a [String] or a [Uri].
+  ///
+  /// Whether or not [uri] is passed, [packageConfigMap] is expected to be
+  /// fully-resolved. That is, any relative URIs in the original package config
+  /// source should be resolved relative to its location.
+  factory SyncPackageResolver.config(Map<String, Uri> packageConfigMap, {uri}) =
+      PackageConfigResolver;
+
+  /// Returns the package resolution strategy for the given [packageRoot], which
+  /// may be a [String] or a [Uri].
+  factory SyncPackageResolver.root(packageRoot) = PackageRootResolver;
+
+  /// Resolves [packageUri] according to this package resolution strategy.
+  ///
+  /// [packageUri] may be a [String] or a [Uri]. This throws a [FormatException]
+  /// if [packageUri] isn't a `package:` URI or doesn't have at least one path
+  /// segment.
+  ///
+  /// If [packageUri] refers to a package that's not in the package spec, this
+  /// returns `null`.
+  Uri resolveUri(packageUri);
+
+  /// Returns the resolved URL for [package] and [path].
+  ///
+  /// This is equivalent to `resolveUri("package:$package/")` or
+  /// `resolveUri("package:$package/$path")`, depending on whether [path] was
+  /// passed.
+  ///
+  /// If [package] refers to a package that's not in the package spec, this
+  /// returns `null`.
+  Uri urlFor(String package, [String path]);
+
+  /// Returns the `package:` URI for [url].
+  ///
+  /// If [url] can't be referred to using a `package:` URI, returns `null`.
+  ///
+  /// [url] may be a [String] or a [Uri].
+  Uri packageUriFor(url);
+
+  /// Returns the path on the local filesystem to the root of [package], or
+  /// `null` if the root cannot be found.
+  ///
+  /// **Note**: this assumes a pub-style package layout. In particular:
+  ///
+  /// * If a package root is being used, this assumes that it contains symlinks
+  ///   to packages' lib/ directories.
+  ///
+  /// * If a package config is being used, this assumes that each entry points
+  ///   to a package's lib/ directory.
+  ///
+  /// If these assumptions are broken, this may return `null` or it may return
+  /// an invalid result.
+  ///
+  /// Returns `null` if the package root is not a `file:` URI, or if the package
+  /// config entry for [package] is not a `file:` URI.
+  String packagePath(String package);
+}