Let docgen detect a dart-sdk directory that's differently named

pkg/docgen/lib/src/package_helpers.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.
 
 library docgen.package_helpers;
 
 import 'exports/source_mirrors.dart';
 import 'generator.dart' show pubScript;
 
 import 'dart:io';
 import 'package:path/path.dart' as path;
 import 'package:yaml/yaml.dart';
 
 /// Helper accessor to determine the full pathname of the root of the dart
 /// checkout. We can be in one of three situations:
 /// 1) Running from pkg/docgen/bin/docgen.dart
 /// 2) Running from a snapshot in a build,
 ///   e.g. xcodebuild/ReleaseIA32/dart-sdk/bin
 /// 3) Running from a built distribution,
 ///   e.g. ...somename/dart-sdk/bin/snapshots
 String get rootDirectory {
   if (_rootDirectoryCache != null) return _rootDirectoryCache;
   var scriptDir = path.absolute(path.dirname(Platform.script.toFilePath()));
   var root = scriptDir;
   var base = path.basename(root);
-  // When we find dart-sdk or sdk we are one level below the root.
-  while (base != 'dart-sdk' && base != 'sdk' && base != 'pkg') {
+  var found = false;
+  // When we find a version file or sdk we are one level below the root.
+  while (!found && base != 'sdk' && base != 'pkg') {
     root = path.dirname(root);
     base = path.basename(root);
+    // Look for something that looks like the dart-sdk directory, which we
+    // expect to be in the path above us and to have a 'version' file containing
+    // the same version as we are running.
+    if (hasMatchingVersionFile(root)) {
+      found = true;
+    }
     if (root == base) {
       // We have reached the root of the filesystem without finding anything.
       throw new FileSystemException("Cannot find SDK directory starting from ",
           scriptDir);
     }
   }
   _rootDirectoryCache = path.dirname(root);
   return _rootDirectoryCache;
 }
 String _rootDirectoryCache;
 
+
+/// Does this directory contain a version file that has the same version as
+/// we do.
+bool hasMatchingVersionFile(String root) {
+  var versionFile = new File(path.join(root, 'version'));
+  if (!versionFile.existsSync()) return false;
+  var version = versionFile.readAsStringSync().trim();
+  var vmVersion = Platform.version;
+  return vmVersion.startsWith(version);
+}
+
 /// Given a LibraryMirror that is a library, return the name of the directory
 /// holding the package information for that library. If the library is not
 /// part of a package, return null.
 String getPackageDirectory(LibraryMirror mirror) {
   var file = mirror.uri.toFilePath();
   // Any file that's in a package will be in a directory of the form
   // packagename/lib/.../filename.dart, so we know that a possible
   // package directory is at least in the directory above the one containing
   // [file]
   var directoryAbove = path.dirname(path.dirname(file));
@@ skipping 66 matching lines @@
   while (!_pubspecFor(dir).existsSync()) {
     var newDir = path.dirname(dir);
     if (newDir == dir) return null;
     dir = newDir;
   }
   return dir;
 }
 
 File _pubspecFor(String directoryName) =>
     new File(path.join(directoryName, 'pubspec.yaml'));