release: merge back stable branch into default

.hgtags

@@ -1,21 +1,22 b''
 c6fad7d1e61f22b1f4a4863eff207a04c27e9462 v4.0.0
 77b6e243b4cc5b702c15abd6d737798edbac60dc v4.0.1
 a359c072337fdd8e1e71df72cc520b8a9b042f80 v4.1.0
 49aa7ed030a36b7ceba149a21e587cb5d20b4946 v4.1.1
 f38ed1e1a31dce3c170b4d31585ba43471cf0705 v4.1.2
 21269ba7bafd8f0c77e79dd86a31eb9bce7643d2 v4.2.0
 b53930c918c25b2c8f69ceddc6641e511be27fd3 v4.2.1
 6627ff4119723d8b2b60918e8b1aa49e9f055aab v4.3.0
 d38f2c2b861dde6c4178923f7cf15ea58b85aa92 v4.3.1
 1232313f9e6adac5ce5399c2a891dc1e72b79022 v4.4.0
 cbb9f1d329ae5768379cdec55a62ebdd546c4e27 v4.4.1
 24ffe44a27fcd1c5b6936144e176b9f6dd2f3a17 v4.4.2
 beaeeaa440cd17471110d4621b8816506c0dff4a v4.5.0
 668e5c656f61dd94595611844e1106d1361aa6a7 v4.5.1
 ae0640240cb7a77e6dc8c77e64dd80d79732cb5b v4.5.2
 7af06899f426813583fe60449d7517cc49c15b28 v4.6.0
 8f7f4299bf341b43f94dadafa1ea73d6cea2c9ba v4.6.1
 de00a831a0709ffaac57f948738ea927b97223a9 v4.7.0
 57f527e0646d731768fb5e0fe742b12a35bdc63b v4.7.1
 f9b09787da9845e4a105f4bffdc252099902cefb v4.7.2
 0b7c790b726f08385e6ebdf4f257c905787b9244 v4.8.0
+f4123e725b74d0e82fe89982ab8791a66062e2b3 v4.9.0

vcsserver/svn.py

@@ -1,668 +1,679 b''
 # RhodeCode VCSServer provides access to different vcs backends via network.
 # Copyright (C) 2014-2017 RodeCode GmbH
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
 # the Free Software Foundation; either version 3 of the License, or
 # (at your option) any later version.
 #
 # This program is distributed in the hope that it will be useful,
 # but WITHOUT ANY WARRANTY; without even the implied warranty of
 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 # GNU General Public License for more details.
 #
 # You should have received a copy of the GNU General Public License
 # along with this program; if not, write to the Free Software Foundation,
 # Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301  USA
 
 from __future__ import absolute_import
 
+import os
 from urllib2 import URLError
 import logging
 import posixpath as vcspath
 import StringIO
 import subprocess
 import urllib
 import traceback
 
 import svn.client
 import svn.core
 import svn.delta
 import svn.diff
 import svn.fs
 import svn.repos
 
 from vcsserver import svn_diff
 from vcsserver import exceptions
 from vcsserver.base import RepoFactory, raise_from_original
 
 
 log = logging.getLogger(__name__)
 
 
 # Set of svn compatible version flags.
 # Compare with subversion/svnadmin/svnadmin.c
 svn_compatible_versions = set([
     'pre-1.4-compatible',
     'pre-1.5-compatible',
     'pre-1.6-compatible',
     'pre-1.8-compatible',
     'pre-1.9-compatible',
 ])
 
 svn_compatible_versions_map = {
     'pre-1.4-compatible': '1.3',
     'pre-1.5-compatible': '1.4',
     'pre-1.6-compatible': '1.5',
     'pre-1.8-compatible': '1.7',
     'pre-1.9-compatible': '1.8',
 }
 
 
 def reraise_safe_exceptions(func):
     """Decorator for converting svn exceptions to something neutral."""
     def wrapper(*args, **kwargs):
         try:
             return func(*args, **kwargs)
         except Exception as e:
             if not hasattr(e, '_vcs_kind'):
                 log.exception("Unhandled exception in hg remote call")
                 raise_from_original(exceptions.UnhandledException)
             raise
     return wrapper
 
 
 class SubversionFactory(RepoFactory):
 
     def _create_repo(self, wire, create, compatible_version):
         path = svn.core.svn_path_canonicalize(wire['path'])
         if create:
             fs_config = {'compatible-version': '1.9'}
             if compatible_version:
                 if compatible_version not in svn_compatible_versions:
                     raise Exception('Unknown SVN compatible version "{}"'
                                     .format(compatible_version))
                 fs_config['compatible-version'] = \
                     svn_compatible_versions_map[compatible_version]
 
             log.debug('Create SVN repo with config "%s"', fs_config)
             repo = svn.repos.create(path, "", "", None, fs_config)
         else:
             repo = svn.repos.open(path)
+
+        log.debug('Got SVN object: %s', repo)
         return repo
 
     def repo(self, wire, create=False, compatible_version=None):
         def create_new_repo():
             return self._create_repo(wire, create, compatible_version)
 
         return self._repo(wire, create_new_repo)
 
 
 NODE_TYPE_MAPPING = {
     svn.core.svn_node_file: 'file',
     svn.core.svn_node_dir: 'dir',
 }
 
 
 class SvnRemote(object):
 
     def __init__(self, factory, hg_factory=None):
         self._factory = factory
         # TODO: Remove once we do not use internal Mercurial objects anymore
         # for subversion
         self._hg_factory = hg_factory
 
     @reraise_safe_exceptions
     def discover_svn_version(self):
         try:
             import svn.core
             svn_ver = svn.core.SVN_VERSION
         except ImportError:
             svn_ver = None
         return svn_ver
 
     def check_url(self, url, config_items):
         # this can throw exception if not installed, but we detect this
         from hgsubversion import svnrepo
 
         baseui = self._hg_factory._create_config(config_items)
         # uuid function get's only valid UUID from proper repo, else
         # throws exception
         try:
             svnrepo.svnremoterepo(baseui, url).svn.uuid
         except Exception:
             tb = traceback.format_exc()
             log.debug("Invalid Subversion url: `%s`, tb: %s", url, tb)
             raise URLError(
                 '"%s" is not a valid Subversion source url.' % (url, ))
         return True
 
     def is_path_valid_repository(self, wire, path):
+
+        # NOTE(marcink):  short circuit the check for SVN repo
+        # the repos.open might be expensive to check, but we have one cheap
+        # pre condition that we can use, to check for 'format' file
+
+        if not os.path.isfile(os.path.join(path, 'format')):
+            return False
+
         try:
             svn.repos.open(path)
         except svn.core.SubversionException:
             tb = traceback.format_exc()
             log.debug("Invalid Subversion path `%s`, tb: %s", path, tb)
             return False
         return True
 
     @reraise_safe_exceptions
     def verify(self, wire,):
         repo_path = wire['path']
         if not self.is_path_valid_repository(wire, repo_path):
             raise Exception(
                 "Path %s is not a valid Subversion repository." % repo_path)
 
         load = subprocess.Popen(
             ['svnadmin', 'info', repo_path],
             stdout=subprocess.PIPE, stderr=subprocess.PIPE)
         return ''.join(load.stdout)
 
     def lookup(self, wire, revision):
         if revision not in [-1, None, 'HEAD']:
             raise NotImplementedError
         repo = self._factory.repo(wire)
         fs_ptr = svn.repos.fs(repo)
         head = svn.fs.youngest_rev(fs_ptr)
         return head
 
     def lookup_interval(self, wire, start_ts, end_ts):
         repo = self._factory.repo(wire)
         fsobj = svn.repos.fs(repo)
         start_rev = None
         end_rev = None
         if start_ts:
             start_ts_svn = apr_time_t(start_ts)
             start_rev = svn.repos.dated_revision(repo, start_ts_svn) + 1
         else:
             start_rev = 1
         if end_ts:
             end_ts_svn = apr_time_t(end_ts)
             end_rev = svn.repos.dated_revision(repo, end_ts_svn)
         else:
             end_rev = svn.fs.youngest_rev(fsobj)
         return start_rev, end_rev
 
     def revision_properties(self, wire, revision):
         repo = self._factory.repo(wire)
         fs_ptr = svn.repos.fs(repo)
         return svn.fs.revision_proplist(fs_ptr, revision)
 
     def revision_changes(self, wire, revision):
 
         repo = self._factory.repo(wire)
         fsobj = svn.repos.fs(repo)
         rev_root = svn.fs.revision_root(fsobj, revision)
 
         editor = svn.repos.ChangeCollector(fsobj, rev_root)
         editor_ptr, editor_baton = svn.delta.make_editor(editor)
         base_dir = ""
         send_deltas = False
         svn.repos.replay2(
             rev_root, base_dir, svn.core.SVN_INVALID_REVNUM, send_deltas,
             editor_ptr, editor_baton, None)
 
         added = []
         changed = []
         removed = []
 
         # TODO: CHANGE_ACTION_REPLACE: Figure out where it belongs
         for path, change in editor.changes.iteritems():
             # TODO: Decide what to do with directory nodes. Subversion can add
             # empty directories.
 
             if change.item_kind == svn.core.svn_node_dir:
                 continue
             if change.action in [svn.repos.CHANGE_ACTION_ADD]:
                 added.append(path)
             elif change.action in [svn.repos.CHANGE_ACTION_MODIFY,
                                    svn.repos.CHANGE_ACTION_REPLACE]:
                 changed.append(path)
             elif change.action in [svn.repos.CHANGE_ACTION_DELETE]:
                 removed.append(path)
             else:
                 raise NotImplementedError(
                     "Action %s not supported on path %s" % (
                         change.action, path))
 
         changes = {
             'added': added,
             'changed': changed,
             'removed': removed,
         }
         return changes
 
     def node_history(self, wire, path, revision, limit):
         cross_copies = False
         repo = self._factory.repo(wire)
         fsobj = svn.repos.fs(repo)
         rev_root = svn.fs.revision_root(fsobj, revision)
 
         history_revisions = []
         history = svn.fs.node_history(rev_root, path)
         history = svn.fs.history_prev(history, cross_copies)
         while history:
             __, node_revision = svn.fs.history_location(history)
             history_revisions.append(node_revision)
             if limit and len(history_revisions) >= limit:
                 break
             history = svn.fs.history_prev(history, cross_copies)
         return history_revisions
 
     def node_properties(self, wire, path, revision):
         repo = self._factory.repo(wire)
         fsobj = svn.repos.fs(repo)
         rev_root = svn.fs.revision_root(fsobj, revision)
         return svn.fs.node_proplist(rev_root, path)
 
     def file_annotate(self, wire, path, revision):
         abs_path = 'file://' + urllib.pathname2url(
             vcspath.join(wire['path'], path))
         file_uri = svn.core.svn_path_canonicalize(abs_path)
 
         start_rev = svn_opt_revision_value_t(0)
         peg_rev = svn_opt_revision_value_t(revision)
         end_rev = peg_rev
 
         annotations = []
 
         def receiver(line_no, revision, author, date, line, pool):
             annotations.append((line_no, revision, line))
 
         # TODO: Cannot use blame5, missing typemap function in the swig code
         try:
             svn.client.blame2(
                 file_uri, peg_rev, start_rev, end_rev,
                 receiver, svn.client.create_context())
         except svn.core.SubversionException as exc:
             log.exception("Error during blame operation.")
             raise Exception(
                 "Blame not supported or file does not exist at path %s. "
                 "Error %s." % (path, exc))
 
         return annotations
 
     def get_node_type(self, wire, path, rev=None):
         repo = self._factory.repo(wire)
         fs_ptr = svn.repos.fs(repo)
         if rev is None:
             rev = svn.fs.youngest_rev(fs_ptr)
         root = svn.fs.revision_root(fs_ptr, rev)
         node = svn.fs.check_path(root, path)
         return NODE_TYPE_MAPPING.get(node, None)
 
     def get_nodes(self, wire, path, revision=None):
         repo = self._factory.repo(wire)
         fsobj = svn.repos.fs(repo)
         if revision is None:
             revision = svn.fs.youngest_rev(fsobj)
         root = svn.fs.revision_root(fsobj, revision)
         entries = svn.fs.dir_entries(root, path)
         result = []
         for entry_path, entry_info in entries.iteritems():
             result.append(
                 (entry_path, NODE_TYPE_MAPPING.get(entry_info.kind, None)))
         return result
 
     def get_file_content(self, wire, path, rev=None):
         repo = self._factory.repo(wire)
         fsobj = svn.repos.fs(repo)
         if rev is None:
             rev = svn.fs.youngest_revision(fsobj)
         root = svn.fs.revision_root(fsobj, rev)
         content = svn.core.Stream(svn.fs.file_contents(root, path))
         return content.read()
 
     def get_file_size(self, wire, path, revision=None):
         repo = self._factory.repo(wire)
         fsobj = svn.repos.fs(repo)
         if revision is None:
             revision = svn.fs.youngest_revision(fsobj)
         root = svn.fs.revision_root(fsobj, revision)
         size = svn.fs.file_length(root, path)
         return size
 
     def create_repository(self, wire, compatible_version=None):
         log.info('Creating Subversion repository in path "%s"', wire['path'])
         self._factory.repo(wire, create=True,
                            compatible_version=compatible_version)
 
     def import_remote_repository(self, wire, src_url):
         repo_path = wire['path']
         if not self.is_path_valid_repository(wire, repo_path):
             raise Exception(
                 "Path %s is not a valid Subversion repository." % repo_path)
         # TODO: johbo: URL checks ?
         rdump = subprocess.Popen(
             ['svnrdump', 'dump', '--non-interactive', src_url],
             stdout=subprocess.PIPE, stderr=subprocess.PIPE)
         load = subprocess.Popen(
             ['svnadmin', 'load', repo_path], stdin=rdump.stdout)
 
         # TODO: johbo: This can be a very long operation, might be better
         # to track some kind of status and provide an api to check if the
         # import is done.
         rdump.wait()
         load.wait()
 
         if rdump.returncode != 0:
             errors = rdump.stderr.read()
             log.error('svnrdump dump failed: statuscode %s: message: %s',
                       rdump.returncode, errors)
             reason = 'UNKNOWN'
             if 'svnrdump: E230001:' in errors:
                 reason = 'INVALID_CERTIFICATE'
             raise Exception(
                 'Failed to dump the remote repository from %s.' % src_url,
                 reason)
         if load.returncode != 0:
             raise Exception(
                 'Failed to load the dump of remote repository from %s.' %
                 (src_url, ))
 
     def commit(self, wire, message, author, timestamp, updated, removed):
         assert isinstance(message, str)
         assert isinstance(author, str)
 
         repo = self._factory.repo(wire)
         fsobj = svn.repos.fs(repo)
 
         rev = svn.fs.youngest_rev(fsobj)
         txn = svn.repos.fs_begin_txn_for_commit(repo, rev, author, message)
         txn_root = svn.fs.txn_root(txn)
 
         for node in updated:
             TxnNodeProcessor(node, txn_root).update()
         for node in removed:
             TxnNodeProcessor(node, txn_root).remove()
 
         commit_id = svn.repos.fs_commit_txn(repo, txn)
 
         if timestamp:
             apr_time = apr_time_t(timestamp)
             ts_formatted = svn.core.svn_time_to_cstring(apr_time)
             svn.fs.change_rev_prop(fsobj, commit_id, 'svn:date', ts_formatted)
 
         log.debug('Committed revision "%s" to "%s".', commit_id, wire['path'])
         return commit_id
 
     def diff(self, wire, rev1, rev2, path1=None, path2=None,
              ignore_whitespace=False, context=3):
 
         wire.update(cache=False)
         repo = self._factory.repo(wire)
         diff_creator = SvnDiffer(
             repo, rev1, path1, rev2, path2, ignore_whitespace, context)
         try:
             return diff_creator.generate_diff()
         except svn.core.SubversionException as e:
             log.exception(
                 "Error during diff operation operation. "
                 "Path might not exist %s, %s" % (path1, path2))
             return ""
 
     @reraise_safe_exceptions
     def is_large_file(self, wire, path):
         return False
 
 
 class SvnDiffer(object):
     """
     Utility to create diffs based on difflib and the Subversion api
     """
 
     binary_content = False
 
     def __init__(
             self, repo, src_rev, src_path, tgt_rev, tgt_path,
             ignore_whitespace, context):
         self.repo = repo
         self.ignore_whitespace = ignore_whitespace
         self.context = context
 
         fsobj = svn.repos.fs(repo)
 
         self.tgt_rev = tgt_rev
         self.tgt_path = tgt_path or ''
         self.tgt_root = svn.fs.revision_root(fsobj, tgt_rev)
         self.tgt_kind = svn.fs.check_path(self.tgt_root, self.tgt_path)
 
         self.src_rev = src_rev
         self.src_path = src_path or self.tgt_path
         self.src_root = svn.fs.revision_root(fsobj, src_rev)
         self.src_kind = svn.fs.check_path(self.src_root, self.src_path)
 
         self._validate()
 
     def _validate(self):
         if (self.tgt_kind != svn.core.svn_node_none and
                 self.src_kind != svn.core.svn_node_none and
                 self.src_kind != self.tgt_kind):
             # TODO: johbo: proper error handling
             raise Exception(
                 "Source and target are not compatible for diff generation. "
                 "Source type: %s, target type: %s" %
                 (self.src_kind, self.tgt_kind))
 
     def generate_diff(self):
         buf = StringIO.StringIO()
         if self.tgt_kind == svn.core.svn_node_dir:
             self._generate_dir_diff(buf)
         else:
             self._generate_file_diff(buf)
         return buf.getvalue()
 
     def _generate_dir_diff(self, buf):
         editor = DiffChangeEditor()
         editor_ptr, editor_baton = svn.delta.make_editor(editor)
         svn.repos.dir_delta2(
             self.src_root,
             self.src_path,
             '',  # src_entry
             self.tgt_root,
             self.tgt_path,
             editor_ptr, editor_baton,
             authorization_callback_allow_all,
             False,  # text_deltas
             svn.core.svn_depth_infinity,  # depth
             False,  # entry_props
             False,  # ignore_ancestry
         )
 
         for path, __, change in sorted(editor.changes):
             self._generate_node_diff(
                 buf, change, path, self.tgt_path, path, self.src_path)
 
     def _generate_file_diff(self, buf):
         change = None
         if self.src_kind == svn.core.svn_node_none:
             change = "add"
         elif self.tgt_kind == svn.core.svn_node_none:
             change = "delete"
         tgt_base, tgt_path = vcspath.split(self.tgt_path)
         src_base, src_path = vcspath.split(self.src_path)
         self._generate_node_diff(
             buf, change, tgt_path, tgt_base, src_path, src_base)
 
     def _generate_node_diff(
             self, buf, change, tgt_path, tgt_base, src_path, src_base):
 
         if self.src_rev == self.tgt_rev and tgt_base == src_base:
             # makes consistent behaviour with git/hg to return empty diff if
             # we compare same revisions
             return
 
         tgt_full_path = vcspath.join(tgt_base, tgt_path)
         src_full_path = vcspath.join(src_base, src_path)
 
         self.binary_content = False
         mime_type = self._get_mime_type(tgt_full_path)
 
         if mime_type and not mime_type.startswith('text'):
             self.binary_content = True
             buf.write("=" * 67 + '\n')
             buf.write("Cannot display: file marked as a binary type.\n")
             buf.write("svn:mime-type = %s\n" % mime_type)
         buf.write("Index: %s\n" % (tgt_path, ))
         buf.write("=" * 67 + '\n')
         buf.write("diff --git a/%(tgt_path)s b/%(tgt_path)s\n" % {
             'tgt_path': tgt_path})
 
         if change == 'add':
             # TODO: johbo: SVN is missing a zero here compared to git
             buf.write("new file mode 10644\n")
 
             #TODO(marcink): intro to binary detection of svn patches
             # if self.binary_content:
             #     buf.write('GIT binary patch\n')
 
             buf.write("--- /dev/null\t(revision 0)\n")
             src_lines = []
         else:
             if change == 'delete':
                 buf.write("deleted file mode 10644\n")
 
             #TODO(marcink): intro to binary detection of svn patches
             # if self.binary_content:
             #     buf.write('GIT binary patch\n')
 
             buf.write("--- a/%s\t(revision %s)\n" % (
                 src_path, self.src_rev))
             src_lines = self._svn_readlines(self.src_root, src_full_path)
 
         if change == 'delete':
             buf.write("+++ /dev/null\t(revision %s)\n" % (self.tgt_rev, ))
             tgt_lines = []
         else:
             buf.write("+++ b/%s\t(revision %s)\n" % (
                 tgt_path, self.tgt_rev))
             tgt_lines = self._svn_readlines(self.tgt_root, tgt_full_path)
 
         if not self.binary_content:
             udiff = svn_diff.unified_diff(
                 src_lines, tgt_lines, context=self.context,
                 ignore_blank_lines=self.ignore_whitespace,
                 ignore_case=False,
                 ignore_space_changes=self.ignore_whitespace)
             buf.writelines(udiff)
 
     def _get_mime_type(self, path):
         try:
             mime_type = svn.fs.node_prop(
                 self.tgt_root, path, svn.core.SVN_PROP_MIME_TYPE)
         except svn.core.SubversionException:
             mime_type = svn.fs.node_prop(
                 self.src_root, path, svn.core.SVN_PROP_MIME_TYPE)
         return mime_type
 
     def _svn_readlines(self, fs_root, node_path):
         if self.binary_content:
             return []
         node_kind = svn.fs.check_path(fs_root, node_path)
         if node_kind not in (
                 svn.core.svn_node_file, svn.core.svn_node_symlink):
             return []
         content = svn.core.Stream(
             svn.fs.file_contents(fs_root, node_path)).read()
         return content.splitlines(True)
 
 
 class DiffChangeEditor(svn.delta.Editor):
     """
     Records changes between two given revisions
     """
 
     def __init__(self):
         self.changes = []
 
     def delete_entry(self, path, revision, parent_baton, pool=None):
         self.changes.append((path, None, 'delete'))
 
     def add_file(
             self, path, parent_baton, copyfrom_path, copyfrom_revision,
             file_pool=None):
         self.changes.append((path, 'file', 'add'))
 
     def open_file(self, path, parent_baton, base_revision, file_pool=None):
         self.changes.append((path, 'file', 'change'))
 
 
 def authorization_callback_allow_all(root, path, pool):
     return True
 
 
 class TxnNodeProcessor(object):
     """
     Utility to process the change of one node within a transaction root.
 
     It encapsulates the knowledge of how to add, update or remove
     a node for a given transaction root. The purpose is to support the method
     `SvnRemote.commit`.
     """
 
     def __init__(self, node, txn_root):
         assert isinstance(node['path'], str)
 
         self.node = node
         self.txn_root = txn_root
 
     def update(self):
         self._ensure_parent_dirs()
         self._add_file_if_node_does_not_exist()
         self._update_file_content()
         self._update_file_properties()
 
     def remove(self):
         svn.fs.delete(self.txn_root, self.node['path'])
         # TODO: Clean up directory if empty
 
     def _ensure_parent_dirs(self):
         curdir = vcspath.dirname(self.node['path'])
         dirs_to_create = []
         while not self._svn_path_exists(curdir):
             dirs_to_create.append(curdir)
             curdir = vcspath.dirname(curdir)
 
         for curdir in reversed(dirs_to_create):
             log.debug('Creating missing directory "%s"', curdir)
             svn.fs.make_dir(self.txn_root, curdir)
 
     def _svn_path_exists(self, path):
         path_status = svn.fs.check_path(self.txn_root, path)
         return path_status != svn.core.svn_node_none
 
     def _add_file_if_node_does_not_exist(self):
         kind = svn.fs.check_path(self.txn_root, self.node['path'])
         if kind == svn.core.svn_node_none:
             svn.fs.make_file(self.txn_root, self.node['path'])
 
     def _update_file_content(self):
         assert isinstance(self.node['content'], str)
         handler, baton = svn.fs.apply_textdelta(
             self.txn_root, self.node['path'], None, None)
         svn.delta.svn_txdelta_send_string(self.node['content'], handler, baton)
 
     def _update_file_properties(self):
         properties = self.node.get('properties', {})
         for key, value in properties.iteritems():
             svn.fs.change_node_prop(
                 self.txn_root, self.node['path'], key, value)
 
 
 def apr_time_t(timestamp):
     """
     Convert a Python timestamp into APR timestamp type apr_time_t
     """
     return timestamp * 1E6
 
 
 def svn_opt_revision_value_t(num):
     """
     Put `num` into a `svn_opt_revision_value_t` structure.
     """
     value = svn.core.svn_opt_revision_value_t()
     value.number = num
     revision = svn.core.svn_opt_revision_t()
     revision.kind = svn.core.svn_opt_revision_number
     revision.value = value
     return revision