Support an executable in a symlinked directory.

lib/cli_util.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 cli_util;
 
 import 'dart:io';
 
+import 'package:path/path.dart' as p;
 import 'package:which/which.dart';
 
 /// Return the path to the current Dart SDK. This will return `null` if we are
 /// unable to locate the Dart SDK.
 Directory getSdkDir([List<String> cliArgs]) {
   // Look for --dart-sdk on the command line.
   if (cliArgs != null) {
     int index = cliArgs.indexOf('--dart-sdk');
 
     if (index != -1 && (index + 1 < cliArgs.length)) {
@@ skipping 19 matching lines @@
   // Try and locate the VM using 'which'.
   String executable = whichSync('dart', orElse: () => null);
 
   if (executable != null) {
     // In case Dart is symlinked (e.g. homebrew on Mac) follow symbolic links.
     Link link = new Link(executable);
     if (link.existsSync()) {
       executable = link.resolveSymbolicLinksSync();
     }
 
+    Link parentLink = new Link(p.dirname(executable));
+    if (parentLink.existsSync()) {
+      executable = p.join(
+          parentLink.resolveSymbolicLinksSync(), p.basename(executable));
+    }
+
     File dartVm = new File(executable);
     Directory dir = dartVm.parent.parent;
     if (_isSdkDir(dir)) return dir;
   }
 
   return null;
 }
 
 bool _isSdkDir(Directory dir) => _joinFile(dir, ['version']).existsSync();
 
 File _joinFile(Directory dir, List<String> files) {
   String pathFragment = files.join(Platform.pathSeparator);
   return new File("${dir.path}${Platform.pathSeparator}${pathFragment}");
 }