Fix code_transformers to consider dart symlinks (typical in brew installations)

pkg/code_transformers/lib/src/dart_sdk.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 code_transformers.src.dart_sdk;
 
 import 'dart:convert' as convert;
 import 'dart:io' show File, Platform, Process;
 import 'package:path/path.dart' as path;
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/java_io.dart';
 import 'package:analyzer/src/generated/sdk.dart';
 import 'package:analyzer/src/generated/sdk_io.dart' show DirectoryBasedDartSdk;
 import 'package:analyzer/src/generated/source.dart';
 
 
 /// Attempts to provide the current Dart SDK directory.
 ///
 /// This will return null if the SDK cannot be found
 ///
 /// Note that this may not be correct when executing outside of `pub`.
 String get dartSdkDirectory {
 
   bool isSdkDir(String dirname) =>
       new File(path.join(dirname, 'lib', '_internal', 'libraries.dart'))
-        .existsSync();
+      .existsSync();
 
-  if (path.split(Platform.executable).length == 1) {
+  String executable = Platform.executable;
+  if (path.split(executable).length == 1) {
     // TODO(blois): make this cross-platform.
     // HACK: A single part, hope it's on the path.
-    var result = Process.runSync('which', ['dart'],
-        stdoutEncoding: convert.UTF8);
-
-    var sdkDir = path.dirname(path.dirname(result.stdout));
+    executable = Process.runSync('which', ['dart'],
+        stdoutEncoding: convert.UTF8).stdout.trim();
+    // In case Dart is symlinked (e.g. homebrew on Mac) follow symbolic links.
+    var link = new Link(executable);
+    if (link.existsSync()) {
+      executable = link.resolveSymbolicLinksSync();
+    }
+    var sdkDir = path.dirname(path.dirname(executable));
     if (isSdkDir(sdkDir)) return sdkDir;
   }
-  var dartDir = path.dirname(path.absolute(Platform.executable));
+
+  var dartDir = path.dirname(path.absolute(executable));
   // If there's a sub-dir named dart-sdk then we're most likely executing from
   // a dart enlistment build directory.
   if (isSdkDir(path.join(dartDir, 'dart-sdk'))) {
     return path.join(dartDir, 'dart-sdk');
   }
   // If we can find libraries.dart then it's the root of the SDK.
   if (isSdkDir(dartDir)) return dartDir;
 
   var parts = path.split(dartDir);
   // If the dart executable is within the sdk dir then get the root.
@@ skipping 175 matching lines @@
   UriKind get uriKind => UriKind.DART_URI;
 
   bool get isInSystemLibrary => true;
 
   Source resolveRelative(Uri relativeUri) =>
       throw new UnsupportedError('not expecting relative urls in dart: mocks');
 
   Uri resolveRelativeUri(Uri relativeUri) =>
       throw new UnsupportedError('not expecting relative urls in dart: mocks');
 }