Try harder to detect an existing checkout before 'fetch'ing.

fetch.py

 #!/usr/bin/env python
 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """
 Tool to perform checkouts in one easy command line!
 
 Usage:
   fetch <recipe> [--property=value [--property2=value2 ...]]
@@ skipping 45 matching lines @@
   def init(self):
     pass
 
   def sync(self):
     pass
 
   def run(self, cmd, **kwargs):
     print 'Running: %s' % (' '.join(pipes.quote(x) for x in cmd))
     if self.options.dry_run:
       return 0
-    return subprocess.check_call(cmd, **kwargs)
+    return subprocess.check_output(cmd, **kwargs)
 
 
 class GclientCheckout(Checkout):
 
   def run_gclient(self, *cmd, **kwargs):
     if not spawn.find_executable('gclient'):
       cmd_prefix = (sys.executable, os.path.join(SCRIPT_PATH, 'gclient.py'))
     else:
       cmd_prefix = ('gclient',)
     return self.run(cmd_prefix + cmd, **kwargs)
 
+  def exists(self):
+    try:
+      gclient_root = self.run_gclient('root').strip()
+      return (os.path.exists(os.path.join(gclient_root, '.gclient')) or
+              os.path.exists(os.path.join(os.getcwd(), self.root)))
+    except subprocess.CalledProcessError:
+      pass
+    return os.path.exists(os.path.join(os.getcwd(), self.root))
+
 
 class GitCheckout(Checkout):
 
   def run_git(self, *cmd, **kwargs):
     if sys.platform == 'win32' and not spawn.find_executable('git'):
       git_path = os.path.join(SCRIPT_PATH, 'git.bat')
     else:
       git_path = 'git'
     return self.run((git_path,) + cmd, **kwargs)
 
@@ skipping 25 matching lines @@
     for soln in self.spec['solutions']:
       soln_string= '\n'.join('    "%s": %s,' % (key, _format_literal(value))
                              for key, value in soln.iteritems())
       soln_strings.append('  {\n%s\n  },' % soln_string)
     gclient_spec = 'solutions = [\n%s\n]\n' % '\n'.join(soln_strings)
     extra_keys = ['target_os', 'target_os_only']
     gclient_spec += ''.join('%s = %s\n' % (key, _format_literal(self.spec[key]))
                              for key in extra_keys if key in self.spec)
     return gclient_spec
 
-  def exists(self):
-    return os.path.exists(os.path.join(os.getcwd(), self.root))
-
   def init(self):
     # Configure and do the gclient checkout.
     self.run_gclient('config', '--spec', self._format_spec())
     sync_cmd = ['sync']
     if self.options.nohooks:
       sync_cmd.append('--nohooks')
     if self.options.no_history:
       sync_cmd.append('--no-history')
     if self.spec.get('with_branch_heads', False):
       sync_cmd.append('--with_branch_heads')
@@ skipping 172 matching lines @@
       root: The directory into which the repo expects to be checkout out.
   """
   assert 'type' in spec
   checkout_type = spec['type']
   checkout_spec = spec['%s_spec' % checkout_type]
   try:
     checkout = CheckoutFactory(checkout_type, options, checkout_spec, root)
   except KeyError:
     return 1
   if checkout.exists():
-    print 'You appear to already have a checkout. "fetch" is used only'
-    print 'to get new checkouts. Use "gclient sync" to update the checkout.'
+    print 'Your current directory appears to already contain, or be part of, '
+    print 'a checkout. "fetch" is used only to get new checkouts. Use '
+    print '"gclient sync" to update existing checkouts.'
     print
     print 'Fetch also does not yet deal with partial checkouts, so if fetch'
     print 'failed, delete the checkout and start over (crbug.com/230691).'
     return 1
   return checkout.init()
 
 
 def main():
   options, recipe, props = handle_args(sys.argv)
   spec, root = run_recipe_fetch(recipe, props)
   return run(options, spec, root)
 
 
 if __name__ == '__main__':
   try:
     sys.exit(main())
   except KeyboardInterrupt:
     sys.stderr.write('interrupted\n')
     sys.exit(1)