Normalize handling of the package root in the runner.

lib/src/util/io.dart

 // Copyright (c) 2015, 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.
 
 library test.util.io;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:mirrors';
 
 import 'package:path/path.dart' as p;
 import 'package:pub_semver/pub_semver.dart';
 
 import '../backend/operating_system.dart';
-import '../runner/load_exception.dart';
+import '../runner/application_exception.dart';
 
 /// The root directory of the Dart SDK.
 final String sdkDir =
     p.dirname(p.dirname(Platform.executable));
 
 /// The version of the Dart SDK currently in use.
 final Version _sdkVersion = new Version.parse(
     new File(p.join(p.dirname(p.dirname(Platform.executable)), 'version'))
         .readAsStringSync().trim());
 
@@ skipping 79 matching lines @@
 
   // IPv6 addresses in URLs need to be enclosed in square brackets to avoid
   // URL ambiguity with the ":" in the address.
   if (address.type == InternetAddressType.IP_V6) {
     return new Uri(scheme: "http", host: "[${address.address}]", port: port);
   }
 
   return new Uri(scheme: "http", host: address.address, port: port);
 }
 
-/// Returns the package root for a Dart entrypoint at [path].
+/// Returns the package root at [root].
 ///
-/// If [override] is passed, that's used. If the package root doesn't exist, a
-/// [LoadException] is thrown.
-String packageRootFor(String path, [String override]) {
-  var packageRoot = override == null
-      ? p.join(p.dirname(path), 'packages')
-      : override;
+/// If [override] is passed, that's used. If the package root doesn't exist, an
+/// [ApplicationException] is thrown.
+String packageRootFor(String root, [String override]) {
+  if (root == null) root = p.current;
+  var packageRoot = override == null ? p.join(root, 'packages') : override;
 
   if (!new Directory(packageRoot).existsSync()) {
-    throw new LoadException(path, "Directory $packageRoot does not exist.");
+    throw new ApplicationException(
+        "Directory ${p.prettyUri(p.toUri(packageRoot))} does not exist.");
   }
 
   return packageRoot;
 }
 
 /// The library name must be globally unique, or the wrong library path may be
 /// returned.
 String libraryPath(Symbol libraryName, {String packageRoot}) {
   var lib = currentMirrorSystem().findLibrary(libraryName);
   if (lib.uri.scheme != 'package') return p.fromUri(lib.uri);
 
   // TODO(nweiz): is there a way to avoid assuming this is being run next to a
   // packages directory?.
   if (packageRoot == null) packageRoot = p.absolute('packages');
   return p.join(packageRoot, p.fromUri(lib.uri.path));
 }