Clean up the semantics of io.dart operations w.r.t. symlinks.

utils/tests/pub/install/pub_install_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS d.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 d.file.
 
 library pub_tests;
 
 import 'dart:io';
 
+import '../../../../pkg/pathos/lib/path.dart' as path;
 import '../../../../pkg/scheduled_test/lib/scheduled_test.dart';
 
+import '../../../pub/io.dart';
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 main() {
   initConfig();
 
   group('requires', () {
     integration('a pubspec', () {
       d.dir(appPath, []).create();
 
@@ skipping 86 matching lines @@
 
     schedulePub(args: ['install'],
         output: new RegExp(r"Dependencies installed!$"));
 
     d.dir(packagesPath, [
       d.nothing('foo'),
       d.dir('myapp', [d.file('myapp.dart', 'main() => "myapp";')])
     ]).validate();
   });
 
+  integration('overwrites a broken packages directory symlink', () {
+    d.dir(appPath, [
+      d.appPubspec([]),
+      d.dir('packages'),
+      d.libDir('myapp'),
+      d.dir('bin')
+    ]).create();
+
+    scheduleSymlink(
+        path.join(appPath, 'packages'),
+        path.join(appPath, 'bin', 'packages'));
+
+    schedule(() => deleteEntry(path.join(sandboxDir, appPath, 'packages')));
+
+    schedulePub(args: ['install'],
+        output: new RegExp(r"Dependencies installed!$"));
+
+    d.dir(packagesPath, [
+      d.nothing('foo'),
+      d.dir('myapp', [d.file('myapp.dart', 'main() => "myapp";')])
+    ]).validate();
+  });
+
   group('creates a packages directory in', () {
     integration('"test/" and its subdirectories', () {
       d.dir(appPath, [
         d.appPubspec([]),
         d.libDir('foo'),
         d.dir("test", [d.dir("subtest")])
       ]).create();
 
       schedulePub(args: ['install'],
           output: new RegExp(r"Dependencies installed!$"));
@@ skipping 115 matching lines @@
           d.dir("packages", [
             d.dir("myapp", [
               d.file('foo.dart', 'main() => "foo";')
             ])
           ])
         ])
       ]).validate();
     });
   });
 }