- Add getters for the current packageRoot or packageMap.

sdk/lib/io/platform.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.
 
 part of dart.io;
 
 /**
  * Information about the environment in which the current program is running.
  *
  * Platform provides information such as the operating system,
@@ skipping 158 matching lines @@
 
   /**
    * Returns the flags passed to the executable used to run the script in this
    * isolate. These are the command-line flags between the executable name
    * and the script name. Each fetch of executableArguments returns a new
    * List, containing the flags passed to the executable.
    */
   static List<String> get executableArguments => _Platform.executableArguments;
 
   /**
-   * Returns the value of the --package-root flag passed to the executable
-   * used to run the script in this isolate.  This is the directory in which
-   * Dart packages are looked up.
+   * Returns the package root of the current isolate, if any.
    *
-   * If there is no --package-root flag, then the empty string is returned.
+   * If the isolate is using a [packageMap], this getter returns `null`,
+   * otherwise it returns the package root - a directory that package
+   * URIs are resolved against.
    */
-  static String get packageRoot => _Platform.packageRoot;
+  static Future<Uri> get packageRoot => _Platform.packageRoot;
+
+  /**
+   * Returns the package mapping of the current isolate, if any.
+   *
+   * If the current isolate is using [packageRoot], this getter returns `null`.
+   *
+   * The package map maps package names to a directory that package URIs for
+   * that package are resolved against, or to `null`, if the package name is
+   * not recognized.

[Lasse Reichstein Nielsen, 2015/09/14 12:56:09]

Change to:
  The package map maps recognized package names to a directory that
  package URIs for that package are resolved against.

The "returning null" part is default behavior for maps..

[siva, 2015/09/14 18:12:07]

The comment seems a bit hard to read maybe :
The package map, maps recognized package names to a directory against which
package URIs for that package are resolved.

[Lasse Reichstein Nielsen, 2015/09/15 07:49:53]

I'm not sure how to parse that.

[Ivan Posva, 2015/09/22 09:42:30]

Lasse and I agreed on the following wording:

The package map maps the name of a package that is available to the program, to
a URI that package URIs for that package are resolved against.

+   *
+   * Returns an empty map if the isolate does not have a way to resolve package
+   * URIs.
+   */
+  static Future<Map<String, Uri>> get packageMap => _Platform.packageMap;
 
   /**
    * Returns the version of the current Dart runtime.
    *
    * The returned `String` is formatted as the
    * [semver](http://semver.org) version string of the current dart
    * runtime, possibly followed by whitespace and other version and
    * build details.
    */
   static String get version => _version;
 }