Work around issue 4928.

utils/pub/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 io;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:isolate';
@@ skipping 15 matching lines @@
   var relative = path.relative(entry, from: dir);
   return !path.isAbsolute(relative) && path.split(relative)[0] != '..';
 }
 
 /// Determines if a file or directory exists at [path].
 bool entryExists(String path) =>
   dirExists(path) || fileExists(path) || linkExists(path);
 
 /// Returns whether [link] exists on the file system. This will return `true`
 /// for any symlink, regardless of what it points at or whether it's broken.
-bool linkExists(String path) => new Link(path).existsSync();
+bool linkExists(String link) => new Link(link).existsSync();
 
 /// Returns whether [file] exists on the file system. This will return `true`
 /// for a symlink only if that symlink is unbroken and points to a file.
 bool fileExists(String file) => new File(file).existsSync();
 
 /// Reads the contents of the text file [file].
 String readTextFile(String file) =>
     new File(file).readAsStringSync(encoding: Encoding.UTF_8);
 
 /// Reads the contents of the binary file [file].
@@ skipping 92 matching lines @@
     // Avoid recursive symlinks.
     var resolvedPath = new File(dir).fullPathSync();
     if (listedDirectories.contains(resolvedPath)) return [];
 
     listedDirectories = new Set<String>.from(listedDirectories);
     listedDirectories.add(resolvedPath);
 
     log.io("Listing directory $dir.");
 
     var children = [];
-    for (var entity in new Directory(dir).listSync()) {
+    for (var entity in new Directory(dir).listSync(followLinks: false)) {
+      // TODO(nweiz): remove this when issue 4928 is fixed.
+      if (entity is Link) {
+        var link = entity.path;
+        // We treat broken symlinks as files, in that we don't want to recurse
+        // into them.
+        entity = dirExists(link) ? new Directory(link) : new File(link);
+      }
+
       if (entity is File) {
         var file = entity.path;
         if (!includeHiddenFiles && path.basename(file).startsWith('.')) {
           continue;
         }
         contents.add(file);
       } else if (entity is Directory) {
         var file = entity.path;
         if (!includeHiddenFiles && path.basename(file).startsWith('.')) {
           continue;
@@ skipping 571 matching lines @@
   const PubProcessResult(this.stdout, this.stderr, this.exitCode);
 
   bool get success => exitCode == 0;
 }
 
 /// 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);
 }