Revert "Revert "Adding package:code_transformers for unifying common transformers code""

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 Directory, File, Platform, Process;
+import 'package:path/path.dart' as path;
+
+
+/// Attempts to provide the current Dart SDK directory.
+///
+/// Note that this may not be correct when executing outside of `pub`.
+String get dartSdkDirectory {
+  if (path.split(Platform.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);
+    return path.dirname(path.dirname(result.stdout));
+  }
+  var sdkDir = path.dirname(path.absolute(Platform.executable));
+  // If there's a sub-dir named dart-sdk then we're most likely executing from
+  // a dart enlistment build directory.
+  if (new Directory(path.join(sdkDir, 'dart-sdk')).existsSync()) {
+    return path.join(sdkDir, 'dart-sdk');
+  }
+  // If we can find libraries.dart then it's the root of the SDK.
+  if (new File(path.join(sdkDir, 'lib', '_internal', 'libraries.dart'))
+      .existsSync()) {
+    return sdkDir;
+  }
+
+  var parts = path.split(sdkDir);
+  // If the dart executable is within the sdk dir then get the root.
+  if (parts.contains('dart-sdk')) {
+    return path.joinAll(parts.take(parts.indexOf('dart-sdk') + 1));
+  }
+
+  return sdkDir;
+}