- Add getters for the current packageRoot or packageMap.

sdk/lib/io/platform.dart

Index: sdk/lib/io/platform.dart
diff --git a/sdk/lib/io/platform.dart b/sdk/lib/io/platform.dart
index 56ddea0193b0df98b43e703e0c98828f4eb1e696..345d61083ad3b67b2884f83998d42e3c9d7f3a2c 100644
--- a/sdk/lib/io/platform.dart
+++ b/sdk/lib/io/platform.dart
@@ -176,13 +176,27 @@ class Platform {
   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.