chromite: Switch from execve to import.

bin/chromite

 #!/usr/bin/python
 # Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Wrapper for the chromite shell.
 
 This script is intended to run in several ways:
 - Outside the chroot, it should be _copied_ to someplace that is in the
   path (like depot_tools).  It will search for the right chromite by looking
   for a file 'chromite/shell/main.py' upward based on the CWD.
 - Inside the chroot, it might be _either_ copied to someplace in the path (since
   depot_tools is in the path in the chroot) or it might run from chromite/bin
   directly, which should be in the PATH.  In any case, we'll look for the
   real 'chromite/shell/main.py' based on the environment variable
   CROS_WORKON_SRCROOT, so it doesn't matter what the CWD is.
 
 If you're looking at a copy and want to know where the original looks at, look
 here:
   http://git.chromium.org/gitweb/?p=chromite.git;a=blob;f=bin/chromite
 
 Since this script is _copied_, it should remain small and not use internal libs.
+
 """
 
 # Python imports.
 import os
 import sys
 
-if __name__ == '__main__':
-  # Look relative to CROS_WORKON_SRCROOT if that variable exists.  This is
-  # the "inside the chroot" case.
+def Search(path):
+  """Return an iterator of lists of places to look for chromite."""
+
+  # Look in $CROS_WORKON_SRCROOT first.
   if 'CROS_WORKON_SRCROOT' in os.environ:
-    chromite_path = os.path.join(os.environ['CROS_WORKON_SRCROOT'],
-                                 'chromite', 'shell', 'main.py')
-    if os.path.isfile(chromite_path):
-      # Exec the script, which will never return.
-      os.execv(chromite_path, sys.argv)
-    else:
-      print (
-          "ERROR: Couldn't find the chromite tool.\n"
-          "\n"
-          "You may need to update your chroot.  If you need help, see:\n"
-          "  http://www.chromium.org/chromium-os/developer-guide"
-      )
-      sys.exit(1)
+    yield [os.environ['CROS_WORKON_SRCROOT']]
 
-  # Outside the chroot, search upward until the "parent" dir doesn't change
-  # (on Linux, that means we're at '/').  That is an error case.
-  dir = os.getcwd()
-  prev_dir = None
-  while dir != prev_dir:
-    chromite_path = os.path.join(dir, 'chromite', 'shell', 'main.py')
-    if os.path.isfile(chromite_path):
-      # Add the directory above chromite to PYTHONPATH before executing, so
-      # that "import chromite.abc.xyz" works...
-      env = os.environ.copy()
-      if 'PYTHONPATH' in env:
-        env['PYTHONPATH'] += ':%s' % dir
-      else:
-        env['PYTHONPATH'] = dir
+  # Try the path as is
+  yield []
 
-      # Exec the script, which will never return.
-      os.execve(chromite_path, sys.argv, env)
+  # Search upward until we either end up with a blank dir or the "parent" dir
+  # doesn't change.
+  prev_path = None
+  while path and path != prev_path:
+    yield [path]
+    path, prev_path = os.path.dirname(path), path
 
-    prev_dir = dir
-    dir = os.path.dirname(dir)
 
+for path in Search(os.getcwd()):
+  sys.path = path + sys.path
+  try:
+    import chromite.shell.main
+    break
+  except ImportError, e:
+    # We've got different modules named chromite in the tree, pulling in the
+    # wrong one will break the right one.  So unload it.
+    if 'chromite' in sys.modules:
+      del sys.modules['chromite']
+    sys.path = sys.path[len(path):]
+else:
   # TODO(dianders): Should we actually print out the 'repo init' call that
   # the user should use?
-  print (
+  sys.stderr.write(
       "ERROR: Couldn't find the chromite tool.\n"
       "\n"
       "Please change to a directory inside your Chromium OS source tree\n"
       "and retry.  If you need to setup a Chromium OS source tree, see:\n"
-      "  http://www.chromium.org/chromium-os/developer-guide"
-  )
+      "  http://www.chromium.org/chromium-os/developer-guide\n")
   sys.exit(1)
+
+chromite.shell.main.main()