lastchange: handle the git-but-not-git-svn case

build/util/lastchange.py

 #!/usr/bin/env python
 # Copyright (c) 2010 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.
 
 """
 lastchange.py -- Chromium revision fetching utility.
 """
 
 import optparse
 import os
 import subprocess
 import sys
 
 class VersionInfo(object):
   def __init__(self, url, root, revision):
     self.url = url
     self.root = root
     self.revision = revision
 
 
+def IsGitSVN(directory):
+  """Return true if the directory is managed by git-svn."""
+
+  # To test whether git-svn has been set up, query the config for any
+  # svn-related configuration.  This command exits with an error code
+  # if there aren't any matches, so ignore its output.
+  status = subprocess.call(['git', 'config', '--get-regexp', '^svn'],
+                           stdout=subprocess.PIPE,
+                           stderr=subprocess.PIPE,
+                           cwd=directory)
+  return status == 0
+
+
 def FetchSVNRevision(command, directory):
   """
   Fetch the Subversion branch and revision for the a given directory
   by running the given command (e.g. "svn info").
 
   Errors are swallowed.
 
   Returns:
     a VersionInfo object or None on error.
   """
 
   # Force shell usage under cygwin & win32. This is a workaround for
   # mysterious loss of cwd while invoking cygwin's git.
   # We can't just pass shell=True to Popen, as under win32 this will
   # cause CMD to be used, while we explicitly want a cygwin shell.
   if sys.platform in ('cygwin', 'win32'):
-    command = [ 'sh', '-c', ' '.join(command) ];
+    command = ['sh', '-c', ' '.join(command)]
   try:
     proc = subprocess.Popen(command,
                             stdout=subprocess.PIPE,
                             stderr=subprocess.PIPE,
                             cwd=directory)
   except OSError:
     # command is apparently either not installed or not executable.
     return None
   if not proc:
     return None
@@ skipping 16 matching lines @@
   return VersionInfo(url, root, revision)
 
 
 def FetchVersionInfo(default_lastchange, directory=None):
   """
   Returns the last change (in the form of a branch, revision tuple),
   from some appropriate revision control system.
   """
   version_info = FetchSVNRevision(['svn', 'info'], directory)
   if not version_info:
-    version_info = FetchSVNRevision(['git', 'svn', 'info'], directory)
+    # Check that this is a git-svn repo before running 'git svn info',
+    # as that will hang if not.
+    if IsGitSVN(directory):

[tony, 2011/01/24 17:57:44]

Nit: Maybe merge this condition with the 'not version_info' condition?

+      version_info = FetchSVNRevision(['git', 'svn', 'info'], directory)
   if not version_info:
     if default_lastchange and os.path.exists(default_lastchange):
       revision = open(default_lastchange, 'r').read().strip()
       version_info = VersionInfo(None, None, revision)
     else:
-      version_info = VersionInfo('', '', '0')
+      version_info = VersionInfo('unknown', '', '0')
   return version_info
 
 
 def WriteIfChanged(file_name, contents):
   """
   Writes the specified contents to the specified file_name
   iff the contents are different than the current contents.
   """
   try:
     old_contents = open(file_name, 'r').read()
@@ skipping 38 matching lines @@
     if out_file:
       WriteIfChanged(out_file, contents)
     else:
       sys.stdout.write(contents)
 
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(main())