git-llvm: Add a svn2git command.

[pcc]

Summary

Lacks any sort of caching, but at least it's a start.

llvm/utils/git-svn/git-llvm

log('Pushing %d commit%s:\n%s' %
         (len(revs), 's' if len(revs) != 1
          else '', '\n'.join('  ' + git('show', '--oneline', '--quiet', c)
                             for c in revs)))
     for r in revs:
         clean_and_update_svn(svn_root)
         svn_push_one_rev(svn_root, r, dry_run)
 
 
+def cmd_svn2git(args):
+    '''Map svn revisions onto git revisions.'''
+    dot_git_dir = git('rev-parse', '--git-common-dir')
+    os.chdir(dot_git_dir)
+
+    # refs/notes/commits:09/c4/b68e68c4fcff64b00e1ac077c4f4a524cbcc
+    grep_result = git('grep', '-l', '^git-svn-rev: ' + args.rev + '$', 'refs/notes/commits')
+    print(grep_result.split(':')[1].replace('/', ''))
+
+
 if __name__ == '__main__':
     if not program_exists('svn'):
         die('error: git-llvm needs svn command, but svn is not installed.')
 
     argv = sys.argv[1:]
     p = argparse.ArgumentParser(
         prog='git llvm', formatter_class=argparse.RawDescriptionHelpFormatter,
         description=__doc__)
parser_push.add_argument(
         'rev_range',
         metavar='GIT_REVS',
         type=str,
         nargs='?',
         help="revs to push (default: everything not in the branch's "
         'upstream, or not in origin/master if the branch lacks '
         'an explicit upstream)')
     parser_push.set_defaults(func=cmd_push)
+
+    parser_svn2git = subcommands.add_parser(
+        'svn2git', description=cmd_svn2git.__doc__,
+        help='map svn revisions to git revisions')
+    parser_svn2git.add_argument(
+        'rev',
+        metavar='SVN_REV',
+        type=str,
+        help="rev to map")
+    parser_svn2git.set_defaults(func=cmd_svn2git)
+
     args = p.parse_args(argv)
     VERBOSE = args.verbose
     QUIET = args.quiet
 
     # Dispatch to the right subcommand
     args.func(args)