Resolve symlinks before determining relative path.

sdk/lib/_internal/pub/lib/src/io.dart

 // Copyright (c) 2013, 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.
 
 /// Helper functionality to make working with IO easier.
 library pub.io;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:convert';
@@ skipping 333 matching lines @@
 void createSymlink(String target, String symlink,
     {bool relative: false}) {
   if (relative) {
     // Relative junction points are not supported on Windows. Instead, just
     // make sure we have a clean absolute path because it will interpret a
     // relative path to be relative to the cwd, not the symlink, and will be
     // confused by forward slashes.
     if (Platform.operatingSystem == 'windows') {
       target = path.normalize(path.absolute(target));
     } else {
-      target = path.normalize(
-          path.relative(target, from: path.dirname(symlink)));
+      // If the directory where we're creating the symlink was itself reached
+      // by traversing a symlink, we want the relative path to be relative to
+      // it's actual location, not the one we went through to get to it.
+      var symlinkDir = canonicalize(path.dirname(symlink));
+      target = path.normalize(path.relative(target, from: symlinkDir));
     }
   }
 
   log.fine("Creating $symlink pointing to $target");
   new Link(symlink).createSync(target);
 }
 
 /// Creates a new symlink that creates an alias at [symlink] that points to the
 /// `lib` directory of package [target]. If [target] does not have a `lib`
 /// directory, this shows a warning if appropriate and then does nothing.
@@ skipping 481 matching lines @@
   const PubProcessResult(this.stdout, this.stderr, this.exitCode);
 
   bool get success => exitCode == exit_codes.SUCCESS;
 }
 
 /// Gets a [Uri] for [uri], which can either already be one, or be a [String].
 Uri _getUri(uri) {
   if (uri is Uri) return uri;
   return Uri.parse(uri);
 }