changegroup: pass function to build delta header into constructor

Previously, the delta header struct format was defined on each
class and each class had a separate function for building the
delta header.

We replace both of these with an argument to __init__ containing
a callable that can format a delta header given a revisiondelta
instance.

Differential Revision: https://phab.mercurial-scm.org/D4079

mercurial/changegroup.py

@@ -1,1376 +1,1375 b''
 # changegroup.py - Mercurial changegroup manipulation functions
 #
 #  Copyright 2006 Matt Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from __future__ import absolute_import
 
 import os
 import struct
 import weakref
 
 from .i18n import _
 from .node import (
     hex,
     nullid,
     nullrev,
     short,
 )
 
 from .thirdparty import (
     attr,
 )
 
 from . import (
     dagutil,
     error,
     manifest,
     match as matchmod,
     mdiff,
     phases,
     pycompat,
     repository,
     revlog,
     util,
 )
 
 from .utils import (
     stringutil,
 )
 
 _CHANGEGROUPV1_DELTA_HEADER = struct.Struct("20s20s20s20s")
 _CHANGEGROUPV2_DELTA_HEADER = struct.Struct("20s20s20s20s20s")
 _CHANGEGROUPV3_DELTA_HEADER = struct.Struct(">20s20s20s20s20sH")
 
 LFS_REQUIREMENT = 'lfs'
 
 readexactly = util.readexactly
 
 def getchunk(stream):
     """return the next chunk from stream as a string"""
     d = readexactly(stream, 4)
     l = struct.unpack(">l", d)[0]
     if l <= 4:
         if l:
             raise error.Abort(_("invalid chunk length %d") % l)
         return ""
     return readexactly(stream, l - 4)
 
 def chunkheader(length):
     """return a changegroup chunk header (string)"""
     return struct.pack(">l", length + 4)
 
 def closechunk():
     """return a changegroup chunk header (string) for a zero-length chunk"""
     return struct.pack(">l", 0)
 
 def writechunks(ui, chunks, filename, vfs=None):
     """Write chunks to a file and return its filename.
 
     The stream is assumed to be a bundle file.
     Existing files will not be overwritten.
     If no filename is specified, a temporary file is created.
     """
     fh = None
     cleanup = None
     try:
         if filename:
             if vfs:
                 fh = vfs.open(filename, "wb")
             else:
                 # Increase default buffer size because default is usually
                 # small (4k is common on Linux).
                 fh = open(filename, "wb", 131072)
         else:
             fd, filename = pycompat.mkstemp(prefix="hg-bundle-", suffix=".hg")
             fh = os.fdopen(fd, r"wb")
         cleanup = filename
         for c in chunks:
             fh.write(c)
         cleanup = None
         return filename
     finally:
         if fh is not None:
             fh.close()
         if cleanup is not None:
             if filename and vfs:
                 vfs.unlink(cleanup)
             else:
                 os.unlink(cleanup)
 
 class cg1unpacker(object):
     """Unpacker for cg1 changegroup streams.
 
     A changegroup unpacker handles the framing of the revision data in
     the wire format. Most consumers will want to use the apply()
     method to add the changes from the changegroup to a repository.
 
     If you're forwarding a changegroup unmodified to another consumer,
     use getchunks(), which returns an iterator of changegroup
     chunks. This is mostly useful for cases where you need to know the
     data stream has ended by observing the end of the changegroup.
 
     deltachunk() is useful only if you're applying delta data. Most
     consumers should prefer apply() instead.
 
     A few other public methods exist. Those are used only for
     bundlerepo and some debug commands - their use is discouraged.
     """
     deltaheader = _CHANGEGROUPV1_DELTA_HEADER
     deltaheadersize = deltaheader.size
     version = '01'
     _grouplistcount = 1 # One list of files after the manifests
 
     def __init__(self, fh, alg, extras=None):
         if alg is None:
             alg = 'UN'
         if alg not in util.compengines.supportedbundletypes:
             raise error.Abort(_('unknown stream compression type: %s')
                              % alg)
         if alg == 'BZ':
             alg = '_truncatedBZ'
 
         compengine = util.compengines.forbundletype(alg)
         self._stream = compengine.decompressorreader(fh)
         self._type = alg
         self.extras = extras or {}
         self.callback = None
 
     # These methods (compressed, read, seek, tell) all appear to only
     # be used by bundlerepo, but it's a little hard to tell.
     def compressed(self):
         return self._type is not None and self._type != 'UN'
     def read(self, l):
         return self._stream.read(l)
     def seek(self, pos):
         return self._stream.seek(pos)
     def tell(self):
         return self._stream.tell()
     def close(self):
         return self._stream.close()
 
     def _chunklength(self):
         d = readexactly(self._stream, 4)
         l = struct.unpack(">l", d)[0]
         if l <= 4:
             if l:
                 raise error.Abort(_("invalid chunk length %d") % l)
             return 0
         if self.callback:
             self.callback()
         return l - 4
 
     def changelogheader(self):
         """v10 does not have a changelog header chunk"""
         return {}
 
     def manifestheader(self):
         """v10 does not have a manifest header chunk"""
         return {}
 
     def filelogheader(self):
         """return the header of the filelogs chunk, v10 only has the filename"""
         l = self._chunklength()
         if not l:
             return {}
         fname = readexactly(self._stream, l)
         return {'filename': fname}
 
     def _deltaheader(self, headertuple, prevnode):
         node, p1, p2, cs = headertuple
         if prevnode is None:
             deltabase = p1
         else:
             deltabase = prevnode
         flags = 0
         return node, p1, p2, deltabase, cs, flags
 
     def deltachunk(self, prevnode):
         l = self._chunklength()
         if not l:
             return {}
         headerdata = readexactly(self._stream, self.deltaheadersize)
         header = self.deltaheader.unpack(headerdata)
         delta = readexactly(self._stream, l - self.deltaheadersize)
         node, p1, p2, deltabase, cs, flags = self._deltaheader(header, prevnode)
         return (node, p1, p2, cs, deltabase, delta, flags)
 
     def getchunks(self):
         """returns all the chunks contains in the bundle
 
         Used when you need to forward the binary stream to a file or another
         network API. To do so, it parse the changegroup data, otherwise it will
         block in case of sshrepo because it don't know the end of the stream.
         """
         # For changegroup 1 and 2, we expect 3 parts: changelog, manifestlog,
         # and a list of filelogs. For changegroup 3, we expect 4 parts:
         # changelog, manifestlog, a list of tree manifestlogs, and a list of
         # filelogs.
         #
         # Changelog and manifestlog parts are terminated with empty chunks. The
         # tree and file parts are a list of entry sections. Each entry section
         # is a series of chunks terminating in an empty chunk. The list of these
         # entry sections is terminated in yet another empty chunk, so we know
         # we've reached the end of the tree/file list when we reach an empty
         # chunk that was proceeded by no non-empty chunks.
 
         parts = 0
         while parts < 2 + self._grouplistcount:
             noentries = True
             while True:
                 chunk = getchunk(self)
                 if not chunk:
                     # The first two empty chunks represent the end of the
                     # changelog and the manifestlog portions. The remaining
                     # empty chunks represent either A) the end of individual
                     # tree or file entries in the file list, or B) the end of
                     # the entire list. It's the end of the entire list if there
                     # were no entries (i.e. noentries is True).
                     if parts < 2:
                         parts += 1
                     elif noentries:
                         parts += 1
                     break
                 noentries = False
                 yield chunkheader(len(chunk))
                 pos = 0
                 while pos < len(chunk):
                     next = pos + 2**20
                     yield chunk[pos:next]
                     pos = next
             yield closechunk()
 
     def _unpackmanifests(self, repo, revmap, trp, prog):
         self.callback = prog.increment
         # no need to check for empty manifest group here:
         # if the result of the merge of 1 and 2 is the same in 3 and 4,
         # no new manifest will be created and the manifest group will
         # be empty during the pull
         self.manifestheader()
         deltas = self.deltaiter()
         repo.manifestlog.addgroup(deltas, revmap, trp)
         prog.complete()
         self.callback = None
 
     def apply(self, repo, tr, srctype, url, targetphase=phases.draft,
               expectedtotal=None):
         """Add the changegroup returned by source.read() to this repo.
         srctype is a string like 'push', 'pull', or 'unbundle'.  url is
         the URL of the repo where this changegroup is coming from.
 
         Return an integer summarizing the change to this repo:
         - nothing changed or no source: 0
         - more heads than before: 1+added heads (2..n)
         - fewer heads than before: -1-removed heads (-2..-n)
         - number of heads stays the same: 1
         """
         repo = repo.unfiltered()
         def csmap(x):
             repo.ui.debug("add changeset %s\n" % short(x))
             return len(cl)
 
         def revmap(x):
             return cl.rev(x)
 
         changesets = files = revisions = 0
 
         try:
             # The transaction may already carry source information. In this
             # case we use the top level data. We overwrite the argument
             # because we need to use the top level value (if they exist)
             # in this function.
             srctype = tr.hookargs.setdefault('source', srctype)
             url = tr.hookargs.setdefault('url', url)
             repo.hook('prechangegroup',
                       throw=True, **pycompat.strkwargs(tr.hookargs))
 
             # write changelog data to temp files so concurrent readers
             # will not see an inconsistent view
             cl = repo.changelog
             cl.delayupdate(tr)
             oldheads = set(cl.heads())
 
             trp = weakref.proxy(tr)
             # pull off the changeset group
             repo.ui.status(_("adding changesets\n"))
             clstart = len(cl)
             progress = repo.ui.makeprogress(_('changesets'), unit=_('chunks'),
                                             total=expectedtotal)
             self.callback = progress.increment
 
             efiles = set()
             def onchangelog(cl, node):
                 efiles.update(cl.readfiles(node))
 
             self.changelogheader()
             deltas = self.deltaiter()
             cgnodes = cl.addgroup(deltas, csmap, trp, addrevisioncb=onchangelog)
             efiles = len(efiles)
 
             if not cgnodes:
                 repo.ui.develwarn('applied empty changegroup',
                                   config='warn-empty-changegroup')
             clend = len(cl)
             changesets = clend - clstart
             progress.complete()
             self.callback = None
 
             # pull off the manifest group
             repo.ui.status(_("adding manifests\n"))
             # We know that we'll never have more manifests than we had
             # changesets.
             progress = repo.ui.makeprogress(_('manifests'), unit=_('chunks'),
                                             total=changesets)
             self._unpackmanifests(repo, revmap, trp, progress)
 
             needfiles = {}
             if repo.ui.configbool('server', 'validate'):
                 cl = repo.changelog
                 ml = repo.manifestlog
                 # validate incoming csets have their manifests
                 for cset in pycompat.xrange(clstart, clend):
                     mfnode = cl.changelogrevision(cset).manifest
                     mfest = ml[mfnode].readdelta()
                     # store file cgnodes we must see
                     for f, n in mfest.iteritems():
                         needfiles.setdefault(f, set()).add(n)
 
             # process the files
             repo.ui.status(_("adding file changes\n"))
             newrevs, newfiles = _addchangegroupfiles(
                 repo, self, revmap, trp, efiles, needfiles)
             revisions += newrevs
             files += newfiles
 
             deltaheads = 0
             if oldheads:
                 heads = cl.heads()
                 deltaheads = len(heads) - len(oldheads)
                 for h in heads:
                     if h not in oldheads and repo[h].closesbranch():
                         deltaheads -= 1
             htext = ""
             if deltaheads:
                 htext = _(" (%+d heads)") % deltaheads
 
             repo.ui.status(_("added %d changesets"
                              " with %d changes to %d files%s\n")
                              % (changesets, revisions, files, htext))
             repo.invalidatevolatilesets()
 
             if changesets > 0:
                 if 'node' not in tr.hookargs:
                     tr.hookargs['node'] = hex(cl.node(clstart))
                     tr.hookargs['node_last'] = hex(cl.node(clend - 1))
                     hookargs = dict(tr.hookargs)
                 else:
                     hookargs = dict(tr.hookargs)
                     hookargs['node'] = hex(cl.node(clstart))
                     hookargs['node_last'] = hex(cl.node(clend - 1))
                 repo.hook('pretxnchangegroup',
                           throw=True, **pycompat.strkwargs(hookargs))
 
             added = [cl.node(r) for r in pycompat.xrange(clstart, clend)]
             phaseall = None
             if srctype in ('push', 'serve'):
                 # Old servers can not push the boundary themselves.
                 # New servers won't push the boundary if changeset already
                 # exists locally as secret
                 #
                 # We should not use added here but the list of all change in
                 # the bundle
                 if repo.publishing():
                     targetphase = phaseall = phases.public
                 else:
                     # closer target phase computation
 
                     # Those changesets have been pushed from the
                     # outside, their phases are going to be pushed
                     # alongside. Therefor `targetphase` is
                     # ignored.
                     targetphase = phaseall = phases.draft
             if added:
                 phases.registernew(repo, tr, targetphase, added)
             if phaseall is not None:
                 phases.advanceboundary(repo, tr, phaseall, cgnodes)
 
             if changesets > 0:
 
                 def runhooks():
                     # These hooks run when the lock releases, not when the
                     # transaction closes. So it's possible for the changelog
                     # to have changed since we last saw it.
                     if clstart >= len(repo):
                         return
 
                     repo.hook("changegroup", **pycompat.strkwargs(hookargs))
 
                     for n in added:
                         args = hookargs.copy()
                         args['node'] = hex(n)
                         del args['node_last']
                         repo.hook("incoming", **pycompat.strkwargs(args))
 
                     newheads = [h for h in repo.heads()
                                 if h not in oldheads]
                     repo.ui.log("incoming",
                                 "%d incoming changes - new heads: %s\n",
                                 len(added),
                                 ', '.join([hex(c[:6]) for c in newheads]))
 
                 tr.addpostclose('changegroup-runhooks-%020i' % clstart,
                                 lambda tr: repo._afterlock(runhooks))
         finally:
             repo.ui.flush()
         # never return 0 here:
         if deltaheads < 0:
             ret = deltaheads - 1
         else:
             ret = deltaheads + 1
         return ret
 
     def deltaiter(self):
         """
         returns an iterator of the deltas in this changegroup
 
         Useful for passing to the underlying storage system to be stored.
         """
         chain = None
         for chunkdata in iter(lambda: self.deltachunk(chain), {}):
             # Chunkdata: (node, p1, p2, cs, deltabase, delta, flags)
             yield chunkdata
             chain = chunkdata[0]
 
 class cg2unpacker(cg1unpacker):
     """Unpacker for cg2 streams.
 
     cg2 streams add support for generaldelta, so the delta header
     format is slightly different. All other features about the data
     remain the same.
     """
     deltaheader = _CHANGEGROUPV2_DELTA_HEADER
     deltaheadersize = deltaheader.size
     version = '02'
 
     def _deltaheader(self, headertuple, prevnode):
         node, p1, p2, deltabase, cs = headertuple
         flags = 0
         return node, p1, p2, deltabase, cs, flags
 
 class cg3unpacker(cg2unpacker):
     """Unpacker for cg3 streams.
 
     cg3 streams add support for exchanging treemanifests and revlog
     flags. It adds the revlog flags to the delta header and an empty chunk
     separating manifests and files.
     """
     deltaheader = _CHANGEGROUPV3_DELTA_HEADER
     deltaheadersize = deltaheader.size
     version = '03'
     _grouplistcount = 2 # One list of manifests and one list of files
 
     def _deltaheader(self, headertuple, prevnode):
         node, p1, p2, deltabase, cs, flags = headertuple
         return node, p1, p2, deltabase, cs, flags
 
     def _unpackmanifests(self, repo, revmap, trp, prog):
         super(cg3unpacker, self)._unpackmanifests(repo, revmap, trp, prog)
         for chunkdata in iter(self.filelogheader, {}):
             # If we get here, there are directory manifests in the changegroup
             d = chunkdata["filename"]
             repo.ui.debug("adding %s revisions\n" % d)
             dirlog = repo.manifestlog._revlog.dirlog(d)
             deltas = self.deltaiter()
             if not dirlog.addgroup(deltas, revmap, trp):
                 raise error.Abort(_("received dir revlog group is empty"))
 
 class headerlessfixup(object):
     def __init__(self, fh, h):
         self._h = h
         self._fh = fh
     def read(self, n):
         if self._h:
             d, self._h = self._h[:n], self._h[n:]
             if len(d) < n:
                 d += readexactly(self._fh, n - len(d))
             return d
         return readexactly(self._fh, n)
 
 @attr.s(slots=True, frozen=True)
 class revisiondelta(object):
     """Describes a delta entry in a changegroup.
 
     Captured data is sufficient to serialize the delta into multiple
     formats.
     """
     # 20 byte node of this revision.
     node = attr.ib()
     # 20 byte nodes of parent revisions.
     p1node = attr.ib()
     p2node = attr.ib()
     # 20 byte node of node this delta is against.
     basenode = attr.ib()
     # 20 byte node of changeset revision this delta is associated with.
     linknode = attr.ib()
     # 2 bytes of flags to apply to revision data.
     flags = attr.ib()
     # Iterable of chunks holding raw delta data.
     deltachunks = attr.ib()
 
 class cg1packer(object):
-    deltaheader = _CHANGEGROUPV1_DELTA_HEADER
-
-    def __init__(self, repo, filematcher, version, bundlecaps=None):
+    def __init__(self, repo, filematcher, version, builddeltaheader,
+                 bundlecaps=None):
         """Given a source repo, construct a bundler.
 
         filematcher is a matcher that matches on files to include in the
         changegroup. Used to facilitate sparse changegroups.
 
+        builddeltaheader is a callable that constructs the header for a group
+        delta.
+
         bundlecaps is optional and can be used to specify the set of
         capabilities which can be used to build the bundle. While bundlecaps is
         unused in core Mercurial, extensions rely on this feature to communicate
         capabilities to customize the changegroup packer.
         """
         assert filematcher
         self._filematcher = filematcher
 
         self.version = version
+        self._builddeltaheader = builddeltaheader
 
         # Set of capabilities we can use to build the bundle.
         if bundlecaps is None:
             bundlecaps = set()
         self._bundlecaps = bundlecaps
         # experimental config: bundle.reorder
         reorder = repo.ui.config('bundle', 'reorder')
         if reorder == 'auto':
             reorder = None
         else:
             reorder = stringutil.parsebool(reorder)
         self._repo = repo
         self._reorder = reorder
         if self._repo.ui.verbose and not self._repo.ui.debugflag:
             self._verbosenote = self._repo.ui.note
         else:
             self._verbosenote = lambda s: None
 
     def close(self):
         # Ellipses serving mode.
         getattr(self, 'clrev_to_localrev', {}).clear()
         if getattr(self, 'next_clrev_to_localrev', {}):
             self.clrev_to_localrev = self.next_clrev_to_localrev
             del self.next_clrev_to_localrev
         self.changelog_done = True
 
         return closechunk()
 
     def fileheader(self, fname):
         return chunkheader(len(fname)) + fname
 
     # Extracted both for clarity and for overriding in extensions.
     def _sortgroup(self, store, nodelist, lookup):
         """Sort nodes for change group and turn them into revnums."""
         # Ellipses serving mode.
         #
         # In a perfect world, we'd generate better ellipsis-ified graphs
         # for non-changelog revlogs. In practice, we haven't started doing
         # that yet, so the resulting DAGs for the manifestlog and filelogs
         # are actually full of bogus parentage on all the ellipsis
         # nodes. This has the side effect that, while the contents are
         # correct, the individual DAGs might be completely out of whack in
         # a case like 882681bc3166 and its ancestors (back about 10
         # revisions or so) in the main hg repo.
         #
         # The one invariant we *know* holds is that the new (potentially
         # bogus) DAG shape will be valid if we order the nodes in the
         # order that they're introduced in dramatis personae by the
         # changelog, so what we do is we sort the non-changelog histories
         # by the order in which they are used by the changelog.
         if util.safehasattr(self, 'full_nodes') and self.clnode_to_rev:
             key = lambda n: self.clnode_to_rev[lookup(n)]
             return [store.rev(n) for n in sorted(nodelist, key=key)]
 
         # for generaldelta revlogs, we linearize the revs; this will both be
         # much quicker and generate a much smaller bundle
         if (store._generaldelta and self._reorder is None) or self._reorder:
             dag = dagutil.revlogdag(store)
             return dag.linearize(set(store.rev(n) for n in nodelist))
         else:
             return sorted([store.rev(n) for n in nodelist])
 
     def group(self, nodelist, store, lookup, units=None):
         """Calculate a delta group, yielding a sequence of changegroup chunks
         (strings).
 
         Given a list of changeset revs, return a set of deltas and
         metadata corresponding to nodes. The first delta is
         first parent(nodelist[0]) -> nodelist[0], the receiver is
         guaranteed to have this parent as it has all history before
         these changesets. In the case firstparent is nullrev the
         changegroup starts with a full revision.
 
         If units is not None, progress detail will be generated, units specifies
         the type of revlog that is touched (changelog, manifest, etc.).
         """
         # if we don't have any revisions touched by these changesets, bail
         if len(nodelist) == 0:
             yield self.close()
             return
 
         revs = self._sortgroup(store, nodelist, lookup)
 
         # add the parent of the first rev
         p = store.parentrevs(revs[0])[0]
         revs.insert(0, p)
 
         # build deltas
         progress = None
         if units is not None:
             progress = self._repo.ui.makeprogress(_('bundling'), unit=units,
                                                   total=(len(revs) - 1))
         for r in pycompat.xrange(len(revs) - 1):
             if progress:
                 progress.update(r + 1)
             prev, curr = revs[r], revs[r + 1]
             linknode = lookup(store.node(curr))
             for c in self.revchunk(store, curr, prev, linknode):
                 yield c
 
         if progress:
             progress.complete()
         yield self.close()
 
     # filter any nodes that claim to be part of the known set
     def prune(self, store, missing, commonrevs):
         # TODO this violates storage abstraction for manifests.
         if isinstance(store, manifest.manifestrevlog):
             if not self._filematcher.visitdir(store._dir[:-1] or '.'):
                 return []
 
         rr, rl = store.rev, store.linkrev
         return [n for n in missing if rl(rr(n)) not in commonrevs]
 
     def _packmanifests(self, dir, mfnodes, lookuplinknode):
         """Pack flat manifests into a changegroup stream."""
         assert not dir
         for chunk in self.group(mfnodes, self._repo.manifestlog._revlog,
                                 lookuplinknode, units=_('manifests')):
             yield chunk
 
     def _manifestsdone(self):
         return ''
 
     def generate(self, commonrevs, clnodes, fastpathlinkrev, source):
         '''yield a sequence of changegroup chunks (strings)'''
         repo = self._repo
         cl = repo.changelog
 
         clrevorder = {}
         mfs = {} # needed manifests
         fnodes = {} # needed file nodes
         mfl = repo.manifestlog
         # TODO violates storage abstraction.
         mfrevlog = mfl._revlog
         changedfiles = set()
 
         ellipsesmode = util.safehasattr(self, 'full_nodes')
 
         # Callback for the changelog, used to collect changed files and
         # manifest nodes.
         # Returns the linkrev node (identity in the changelog case).
         def lookupcl(x):
             c = cl.read(x)
             clrevorder[x] = len(clrevorder)
 
             if ellipsesmode:
                 # Only update mfs if x is going to be sent. Otherwise we
                 # end up with bogus linkrevs specified for manifests and
                 # we skip some manifest nodes that we should otherwise
                 # have sent.
                 if (x in self.full_nodes
                     or cl.rev(x) in self.precomputed_ellipsis):
                     n = c[0]
                     # Record the first changeset introducing this manifest
                     # version.
                     mfs.setdefault(n, x)
                     # Set this narrow-specific dict so we have the lowest
                     # manifest revnum to look up for this cl revnum. (Part of
                     # mapping changelog ellipsis parents to manifest ellipsis
                     # parents)
                     self.next_clrev_to_localrev.setdefault(cl.rev(x),
                                                            mfrevlog.rev(n))
                 # We can't trust the changed files list in the changeset if the
                 # client requested a shallow clone.
                 if self.is_shallow:
                     changedfiles.update(mfl[c[0]].read().keys())
                 else:
                     changedfiles.update(c[3])
             else:
 
                 n = c[0]
                 # record the first changeset introducing this manifest version
                 mfs.setdefault(n, x)
                 # Record a complete list of potentially-changed files in
                 # this manifest.
                 changedfiles.update(c[3])
 
             return x
 
         self._verbosenote(_('uncompressed size of bundle content:\n'))
         size = 0
         for chunk in self.group(clnodes, cl, lookupcl, units=_('changesets')):
             size += len(chunk)
             yield chunk
         self._verbosenote(_('%8.i (changelog)\n') % size)
 
         # We need to make sure that the linkrev in the changegroup refers to
         # the first changeset that introduced the manifest or file revision.
         # The fastpath is usually safer than the slowpath, because the filelogs
         # are walked in revlog order.
         #
         # When taking the slowpath with reorder=None and the manifest revlog
         # uses generaldelta, the manifest may be walked in the "wrong" order.
         # Without 'clrevorder', we would get an incorrect linkrev (see fix in
         # cc0ff93d0c0c).
         #
         # When taking the fastpath, we are only vulnerable to reordering
         # of the changelog itself. The changelog never uses generaldelta, so
         # it is only reordered when reorder=True. To handle this case, we
         # simply take the slowpath, which already has the 'clrevorder' logic.
         # This was also fixed in cc0ff93d0c0c.
         fastpathlinkrev = fastpathlinkrev and not self._reorder
         # Treemanifests don't work correctly with fastpathlinkrev
         # either, because we don't discover which directory nodes to
         # send along with files. This could probably be fixed.
         fastpathlinkrev = fastpathlinkrev and (
             'treemanifest' not in repo.requirements)
 
         for chunk in self.generatemanifests(commonrevs, clrevorder,
                 fastpathlinkrev, mfs, fnodes, source):
             yield chunk
 
         if ellipsesmode:
             mfdicts = None
             if self.is_shallow:
                 mfdicts = [(self._repo.manifestlog[n].read(), lr)
                            for (n, lr) in mfs.iteritems()]
 
         mfs.clear()
         clrevs = set(cl.rev(x) for x in clnodes)
 
         if not fastpathlinkrev:
             def linknodes(unused, fname):
                 return fnodes.get(fname, {})
         else:
             cln = cl.node
             def linknodes(filerevlog, fname):
                 llr = filerevlog.linkrev
                 fln = filerevlog.node
                 revs = ((r, llr(r)) for r in filerevlog)
                 return dict((fln(r), cln(lr)) for r, lr in revs if lr in clrevs)
 
         if ellipsesmode:
             # We need to pass the mfdicts variable down into
             # generatefiles(), but more than one command might have
             # wrapped generatefiles so we can't modify the function
             # signature. Instead, we pass the data to ourselves using an
             # instance attribute. I'm sorry.
             self._mfdicts = mfdicts
 
         for chunk in self.generatefiles(changedfiles, linknodes, commonrevs,
                                         source):
             yield chunk
 
         yield self.close()
 
         if clnodes:
             repo.hook('outgoing', node=hex(clnodes[0]), source=source)
 
     def generatemanifests(self, commonrevs, clrevorder, fastpathlinkrev, mfs,
                           fnodes, source):
         """Returns an iterator of changegroup chunks containing manifests.
 
         `source` is unused here, but is used by extensions like remotefilelog to
         change what is sent based in pulls vs pushes, etc.
         """
         repo = self._repo
         mfl = repo.manifestlog
         dirlog = mfl._revlog.dirlog
         tmfnodes = {'': mfs}
 
         # Callback for the manifest, used to collect linkrevs for filelog
         # revisions.
         # Returns the linkrev node (collected in lookupcl).
         def makelookupmflinknode(dir, nodes):
             if fastpathlinkrev:
                 assert not dir
                 return mfs.__getitem__
 
             def lookupmflinknode(x):
                 """Callback for looking up the linknode for manifests.
 
                 Returns the linkrev node for the specified manifest.
 
                 SIDE EFFECT:
 
                 1) fclnodes gets populated with the list of relevant
                    file nodes if we're not using fastpathlinkrev
                 2) When treemanifests are in use, collects treemanifest nodes
                    to send
 
                 Note that this means manifests must be completely sent to
                 the client before you can trust the list of files and
                 treemanifests to send.
                 """
                 clnode = nodes[x]
                 mdata = mfl.get(dir, x).readfast(shallow=True)
                 for p, n, fl in mdata.iterentries():
                     if fl == 't': # subdirectory manifest
                         subdir = dir + p + '/'
                         tmfclnodes = tmfnodes.setdefault(subdir, {})
                         tmfclnode = tmfclnodes.setdefault(n, clnode)
                         if clrevorder[clnode] < clrevorder[tmfclnode]:
                             tmfclnodes[n] = clnode
                     else:
                         f = dir + p
                         fclnodes = fnodes.setdefault(f, {})
                         fclnode = fclnodes.setdefault(n, clnode)
                         if clrevorder[clnode] < clrevorder[fclnode]:
                             fclnodes[n] = clnode
                 return clnode
             return lookupmflinknode
 
         size = 0
         while tmfnodes:
             dir, nodes = tmfnodes.popitem()
             prunednodes = self.prune(dirlog(dir), nodes, commonrevs)
             if not dir or prunednodes:
                 for x in self._packmanifests(dir, prunednodes,
                                              makelookupmflinknode(dir, nodes)):
                     size += len(x)
                     yield x
         self._verbosenote(_('%8.i (manifests)\n') % size)
         yield self._manifestsdone()
 
     # The 'source' parameter is useful for extensions
     def generatefiles(self, changedfiles, linknodes, commonrevs, source):
         changedfiles = list(filter(self._filematcher, changedfiles))
 
         if getattr(self, 'is_shallow', False):
             # See comment in generate() for why this sadness is a thing.
             mfdicts = self._mfdicts
             del self._mfdicts
             # In a shallow clone, the linknodes callback needs to also include
             # those file nodes that are in the manifests we sent but weren't
             # introduced by those manifests.
             commonctxs = [self._repo[c] for c in commonrevs]
             oldlinknodes = linknodes
             clrev = self._repo.changelog.rev
 
             # Defining this function has a side-effect of overriding the
             # function of the same name that was passed in as an argument.
             # TODO have caller pass in appropriate function.
             def linknodes(flog, fname):
                 for c in commonctxs:
                     try:
                         fnode = c.filenode(fname)
                         self.clrev_to_localrev[c.rev()] = flog.rev(fnode)
                     except error.ManifestLookupError:
                         pass
                 links = oldlinknodes(flog, fname)
                 if len(links) != len(mfdicts):
                     for mf, lr in mfdicts:
                         fnode = mf.get(fname, None)
                         if fnode in links:
                             links[fnode] = min(links[fnode], lr, key=clrev)
                         elif fnode:
                             links[fnode] = lr
                 return links
 
         return self._generatefiles(changedfiles, linknodes, commonrevs, source)
 
     def _generatefiles(self, changedfiles, linknodes, commonrevs, source):
         repo = self._repo
         progress = repo.ui.makeprogress(_('bundling'), unit=_('files'),
                                         total=len(changedfiles))
         for i, fname in enumerate(sorted(changedfiles)):
             filerevlog = repo.file(fname)
             if not filerevlog:
                 raise error.Abort(_("empty or missing file data for %s") %
                                   fname)
 
             linkrevnodes = linknodes(filerevlog, fname)
             # Lookup for filenodes, we collected the linkrev nodes above in the
             # fastpath case and with lookupmf in the slowpath case.
             def lookupfilelog(x):
                 return linkrevnodes[x]
 
             filenodes = self.prune(filerevlog, linkrevnodes, commonrevs)
             if filenodes:
                 progress.update(i + 1, item=fname)
                 h = self.fileheader(fname)
                 size = len(h)
                 yield h
                 for chunk in self.group(filenodes, filerevlog, lookupfilelog):
                     size += len(chunk)
                     yield chunk
                 self._verbosenote(_('%8.i  %s\n') % (size, fname))
         progress.complete()
 
     def deltaparent(self, store, rev, p1, p2, prev):
         if not store.candelta(prev, rev):
             raise error.ProgrammingError('cg1 should not be used in this case')
         return prev
 
     def revchunk(self, store, rev, prev, linknode):
         if util.safehasattr(self, 'full_nodes'):
             fn = self._revisiondeltanarrow
         else:
             fn = self._revisiondeltanormal
 
         delta = fn(store, rev, prev, linknode)
         if not delta:
             return
 
-        meta = self.builddeltaheader(delta.node, delta.p1node, delta.p2node,
-                                     delta.basenode, delta.linknode,
-                                     delta.flags)
+        meta = self._builddeltaheader(delta)
         l = len(meta) + sum(len(x) for x in delta.deltachunks)
 
         yield chunkheader(l)
         yield meta
         for x in delta.deltachunks:
             yield x
 
     def _revisiondeltanormal(self, store, rev, prev, linknode):
         node = store.node(rev)
         p1, p2 = store.parentrevs(rev)
         base = self.deltaparent(store, rev, p1, p2, prev)
 
         prefix = ''
         if store.iscensored(base) or store.iscensored(rev):
             try:
                 delta = store.revision(node, raw=True)
             except error.CensoredNodeError as e:
                 delta = e.tombstone
             if base == nullrev:
                 prefix = mdiff.trivialdiffheader(len(delta))
             else:
                 baselen = store.rawsize(base)
                 prefix = mdiff.replacediffheader(baselen, len(delta))
         elif base == nullrev:
             delta = store.revision(node, raw=True)
             prefix = mdiff.trivialdiffheader(len(delta))
         else:
             delta = store.revdiff(base, rev)
         p1n, p2n = store.parents(node)
 
         return revisiondelta(
             node=node,
             p1node=p1n,
             p2node=p2n,
             basenode=store.node(base),
             linknode=linknode,
             flags=store.flags(rev),
             deltachunks=(prefix, delta),
         )
 
     def _revisiondeltanarrow(self, store, rev, prev, linknode):
         # build up some mapping information that's useful later. See
         # the local() nested function below.
         if not self.changelog_done:
             self.clnode_to_rev[linknode] = rev
             linkrev = rev
             self.clrev_to_localrev[linkrev] = rev
         else:
             linkrev = self.clnode_to_rev[linknode]
             self.clrev_to_localrev[linkrev] = rev
 
         # This is a node to send in full, because the changeset it
         # corresponds to was a full changeset.
         if linknode in self.full_nodes:
             return self._revisiondeltanormal(store, rev, prev, linknode)
 
         # At this point, a node can either be one we should skip or an
         # ellipsis. If it's not an ellipsis, bail immediately.
         if linkrev not in self.precomputed_ellipsis:
             return
 
         linkparents = self.precomputed_ellipsis[linkrev]
         def local(clrev):
             """Turn a changelog revnum into a local revnum.
 
             The ellipsis dag is stored as revnums on the changelog,
             but when we're producing ellipsis entries for
             non-changelog revlogs, we need to turn those numbers into
             something local. This does that for us, and during the
             changelog sending phase will also expand the stored
             mappings as needed.
             """
             if clrev == nullrev:
                 return nullrev
 
             if not self.changelog_done:
                 # If we're doing the changelog, it's possible that we
                 # have a parent that is already on the client, and we
                 # need to store some extra mapping information so that
                 # our contained ellipsis nodes will be able to resolve
                 # their parents.
                 if clrev not in self.clrev_to_localrev:
                     clnode = store.node(clrev)
                     self.clnode_to_rev[clnode] = clrev
                 return clrev
 
             # Walk the ellipsis-ized changelog breadth-first looking for a
             # change that has been linked from the current revlog.
             #
             # For a flat manifest revlog only a single step should be necessary
             # as all relevant changelog entries are relevant to the flat
             # manifest.
             #
             # For a filelog or tree manifest dirlog however not every changelog
             # entry will have been relevant, so we need to skip some changelog
             # nodes even after ellipsis-izing.
             walk = [clrev]
             while walk:
                 p = walk[0]
                 walk = walk[1:]
                 if p in self.clrev_to_localrev:
                     return self.clrev_to_localrev[p]
                 elif p in self.full_nodes:
                     walk.extend([pp for pp in self._repo.changelog.parentrevs(p)
                                     if pp != nullrev])
                 elif p in self.precomputed_ellipsis:
                     walk.extend([pp for pp in self.precomputed_ellipsis[p]
                                     if pp != nullrev])
                 else:
                     # In this case, we've got an ellipsis with parents
                     # outside the current bundle (likely an
                     # incremental pull). We "know" that we can use the
                     # value of this same revlog at whatever revision
                     # is pointed to by linknode. "Know" is in scare
                     # quotes because I haven't done enough examination
                     # of edge cases to convince myself this is really
                     # a fact - it works for all the (admittedly
                     # thorough) cases in our testsuite, but I would be
                     # somewhat unsurprised to find a case in the wild
                     # where this breaks down a bit. That said, I don't
                     # know if it would hurt anything.
                     for i in pycompat.xrange(rev, 0, -1):
                         if store.linkrev(i) == clrev:
                             return i
                     # We failed to resolve a parent for this node, so
                     # we crash the changegroup construction.
                     raise error.Abort(
                         'unable to resolve parent while packing %r %r'
                         ' for changeset %r' % (store.indexfile, rev, clrev))
 
             return nullrev
 
         if not linkparents or (
             store.parentrevs(rev) == (nullrev, nullrev)):
             p1, p2 = nullrev, nullrev
         elif len(linkparents) == 1:
             p1, = sorted(local(p) for p in linkparents)
             p2 = nullrev
         else:
             p1, p2 = sorted(local(p) for p in linkparents)
 
         n = store.node(rev)
         p1n, p2n = store.node(p1), store.node(p2)
         flags = store.flags(rev)
         flags |= revlog.REVIDX_ELLIPSIS
 
         # TODO: try and actually send deltas for ellipsis data blocks
         data = store.revision(n)
         diffheader = mdiff.trivialdiffheader(len(data))
 
         return revisiondelta(
             node=n,
             p1node=p1n,
             p2node=p2n,
             basenode=nullid,
             linknode=linknode,
             flags=flags,
             deltachunks=(diffheader, data),
         )
 
-    def builddeltaheader(self, node, p1n, p2n, basenode, linknode, flags):
-        # do nothing with basenode, it is implicitly the previous one in HG10
-        # do nothing with flags, it is implicitly 0 for cg1 and cg2
-        return self.deltaheader.pack(node, p1n, p2n, linknode)
-
 class cg2packer(cg1packer):
-    deltaheader = _CHANGEGROUPV2_DELTA_HEADER
-
-    def __init__(self, repo, filematcher, version, bundlecaps=None):
+    def __init__(self, repo, filematcher, version, builddeltaheader,
+                 bundlecaps=None):
         super(cg2packer, self).__init__(repo, filematcher, version,
+                                        builddeltaheader,
                                         bundlecaps=bundlecaps)
 
         if self._reorder is None:
             # Since generaldelta is directly supported by cg2, reordering
             # generally doesn't help, so we disable it by default (treating
             # bundle.reorder=auto just like bundle.reorder=False).
             self._reorder = False
 
     def deltaparent(self, store, rev, p1, p2, prev):
         # Narrow ellipses mode.
         if util.safehasattr(self, 'full_nodes'):
             # TODO: send better deltas when in narrow mode.
             #
             # changegroup.group() loops over revisions to send,
             # including revisions we'll skip. What this means is that
             # `prev` will be a potentially useless delta base for all
             # ellipsis nodes, as the client likely won't have it. In
             # the future we should do bookkeeping about which nodes
             # have been sent to the client, and try to be
             # significantly smarter about delta bases. This is
             # slightly tricky because this same code has to work for
             # all revlogs, and we don't have the linkrev/linknode here.
             return p1
 
         dp = store.deltaparent(rev)
         if dp == nullrev and store.storedeltachains:
             # Avoid sending full revisions when delta parent is null. Pick prev
             # in that case. It's tempting to pick p1 in this case, as p1 will
             # be smaller in the common case. However, computing a delta against
             # p1 may require resolving the raw text of p1, which could be
             # expensive. The revlog caches should have prev cached, meaning
             # less CPU for changegroup generation. There is likely room to add
             # a flag and/or config option to control this behavior.
             base = prev
         elif dp == nullrev:
             # revlog is configured to use full snapshot for a reason,
             # stick to full snapshot.
             base = nullrev
         elif dp not in (p1, p2, prev):
             # Pick prev when we can't be sure remote has the base revision.
             return prev
         else:
             base = dp
         if base != nullrev and not store.candelta(base, rev):
             base = nullrev
         return base
 
-    def builddeltaheader(self, node, p1n, p2n, basenode, linknode, flags):
-        # Do nothing with flags, it is implicitly 0 in cg1 and cg2
-        return self.deltaheader.pack(node, p1n, p2n, basenode, linknode)
-
 class cg3packer(cg2packer):
-    deltaheader = _CHANGEGROUPV3_DELTA_HEADER
-
     def _packmanifests(self, dir, mfnodes, lookuplinknode):
         if dir:
             yield self.fileheader(dir)
 
         dirlog = self._repo.manifestlog._revlog.dirlog(dir)
         for chunk in self.group(mfnodes, dirlog, lookuplinknode,
                                 units=_('manifests')):
             yield chunk
 
     def _manifestsdone(self):
         return self.close()
 
-    def builddeltaheader(self, node, p1n, p2n, basenode, linknode, flags):
-        return self.deltaheader.pack(node, p1n, p2n, basenode, linknode, flags)
+def _makecg1packer(repo, filematcher, bundlecaps):
+    builddeltaheader = lambda d: _CHANGEGROUPV1_DELTA_HEADER.pack(
+        d.node, d.p1node, d.p2node, d.linknode)
 
-def _makecg1packer(repo, filematcher, bundlecaps):
-    return cg1packer(repo, filematcher, b'01', bundlecaps=bundlecaps)
+    return cg1packer(repo, filematcher, b'01', builddeltaheader,
+                     bundlecaps=bundlecaps)
 
 def _makecg2packer(repo, filematcher, bundlecaps):
-    return cg2packer(repo, filematcher, b'02', bundlecaps=bundlecaps)
+    builddeltaheader = lambda d: _CHANGEGROUPV2_DELTA_HEADER.pack(
+        d.node, d.p1node, d.p2node, d.basenode, d.linknode)
+
+    return cg2packer(repo, filematcher, b'02', builddeltaheader,
+                     bundlecaps=bundlecaps)
 
 def _makecg3packer(repo, filematcher, bundlecaps):
-    return cg3packer(repo, filematcher, b'03', bundlecaps=bundlecaps)
+    builddeltaheader = lambda d: _CHANGEGROUPV3_DELTA_HEADER.pack(
+        d.node, d.p1node, d.p2node, d.basenode, d.linknode, d.flags)
+
+    return cg3packer(repo, filematcher, b'03', builddeltaheader,
+                     bundlecaps=bundlecaps)
 
 _packermap = {'01': (_makecg1packer, cg1unpacker),
              # cg2 adds support for exchanging generaldelta
              '02': (_makecg2packer, cg2unpacker),
              # cg3 adds support for exchanging revlog flags and treemanifests
              '03': (_makecg3packer, cg3unpacker),
 }
 
 def allsupportedversions(repo):
     versions = set(_packermap.keys())
     if not (repo.ui.configbool('experimental', 'changegroup3') or
             repo.ui.configbool('experimental', 'treemanifest') or
             'treemanifest' in repo.requirements):
         versions.discard('03')
     return versions
 
 # Changegroup versions that can be applied to the repo
 def supportedincomingversions(repo):
     return allsupportedversions(repo)
 
 # Changegroup versions that can be created from the repo
 def supportedoutgoingversions(repo):
     versions = allsupportedversions(repo)
     if 'treemanifest' in repo.requirements:
         # Versions 01 and 02 support only flat manifests and it's just too
         # expensive to convert between the flat manifest and tree manifest on
         # the fly. Since tree manifests are hashed differently, all of history
         # would have to be converted. Instead, we simply don't even pretend to
         # support versions 01 and 02.
         versions.discard('01')
         versions.discard('02')
     if repository.NARROW_REQUIREMENT in repo.requirements:
         # Versions 01 and 02 don't support revlog flags, and we need to
         # support that for stripping and unbundling to work.
         versions.discard('01')
         versions.discard('02')
     if LFS_REQUIREMENT in repo.requirements:
         # Versions 01 and 02 don't support revlog flags, and we need to
         # mark LFS entries with REVIDX_EXTSTORED.
         versions.discard('01')
         versions.discard('02')
 
     return versions
 
 def localversion(repo):
     # Finds the best version to use for bundles that are meant to be used
     # locally, such as those from strip and shelve, and temporary bundles.
     return max(supportedoutgoingversions(repo))
 
 def safeversion(repo):
     # Finds the smallest version that it's safe to assume clients of the repo
     # will support. For example, all hg versions that support generaldelta also
     # support changegroup 02.
     versions = supportedoutgoingversions(repo)
     if 'generaldelta' in repo.requirements:
         versions.discard('01')
     assert versions
     return min(versions)
 
 def getbundler(version, repo, bundlecaps=None, filematcher=None):
     assert version in supportedoutgoingversions(repo)
 
     if filematcher is None:
         filematcher = matchmod.alwaysmatcher(repo.root, '')
 
     if version == '01' and not filematcher.always():
         raise error.ProgrammingError('version 01 changegroups do not support '
                                      'sparse file matchers')
 
     # Requested files could include files not in the local store. So
     # filter those out.
     filematcher = matchmod.intersectmatchers(repo.narrowmatch(),
                                              filematcher)
 
     fn = _packermap[version][0]
     return fn(repo, filematcher, bundlecaps)
 
 def getunbundler(version, fh, alg, extras=None):
     return _packermap[version][1](fh, alg, extras=extras)
 
 def _changegroupinfo(repo, nodes, source):
     if repo.ui.verbose or source == 'bundle':
         repo.ui.status(_("%d changesets found\n") % len(nodes))
     if repo.ui.debugflag:
         repo.ui.debug("list of changesets:\n")
         for node in nodes:
             repo.ui.debug("%s\n" % hex(node))
 
 def makechangegroup(repo, outgoing, version, source, fastpath=False,
                     bundlecaps=None):
     cgstream = makestream(repo, outgoing, version, source,
                           fastpath=fastpath, bundlecaps=bundlecaps)
     return getunbundler(version, util.chunkbuffer(cgstream), None,
                         {'clcount': len(outgoing.missing) })
 
 def makestream(repo, outgoing, version, source, fastpath=False,
                bundlecaps=None, filematcher=None):
     bundler = getbundler(version, repo, bundlecaps=bundlecaps,
                          filematcher=filematcher)
 
     repo = repo.unfiltered()
     commonrevs = outgoing.common
     csets = outgoing.missing
     heads = outgoing.missingheads
     # We go through the fast path if we get told to, or if all (unfiltered
     # heads have been requested (since we then know there all linkrevs will
     # be pulled by the client).
     heads.sort()
     fastpathlinkrev = fastpath or (
             repo.filtername is None and heads == sorted(repo.heads()))
 
     repo.hook('preoutgoing', throw=True, source=source)
     _changegroupinfo(repo, csets, source)
     return bundler.generate(commonrevs, csets, fastpathlinkrev, source)
 
 def _addchangegroupfiles(repo, source, revmap, trp, expectedfiles, needfiles):
     revisions = 0
     files = 0
     progress = repo.ui.makeprogress(_('files'), unit=_('files'),
                                     total=expectedfiles)
     for chunkdata in iter(source.filelogheader, {}):
         files += 1
         f = chunkdata["filename"]
         repo.ui.debug("adding %s revisions\n" % f)
         progress.increment()
         fl = repo.file(f)
         o = len(fl)
         try:
             deltas = source.deltaiter()
             if not fl.addgroup(deltas, revmap, trp):
                 raise error.Abort(_("received file revlog group is empty"))
         except error.CensoredBaseError as e:
             raise error.Abort(_("received delta base is censored: %s") % e)
         revisions += len(fl) - o
         if f in needfiles:
             needs = needfiles[f]
             for new in pycompat.xrange(o, len(fl)):
                 n = fl.node(new)
                 if n in needs:
                     needs.remove(n)
                 else:
                     raise error.Abort(
                         _("received spurious file revlog entry"))
             if not needs:
                 del needfiles[f]
     progress.complete()
 
     for f, needs in needfiles.iteritems():
         fl = repo.file(f)
         for n in needs:
             try:
                 fl.rev(n)
             except error.LookupError:
                 raise error.Abort(
                     _('missing file data for %s:%s - run hg verify') %
                     (f, hex(n)))
 
     return revisions, files
 
 def _packellipsischangegroup(repo, common, match, relevant_nodes,
                              ellipsisroots, visitnodes, depth, source, version):
     if version in ('01', '02'):
         raise error.Abort(
             'ellipsis nodes require at least cg3 on client and server, '
             'but negotiated version %s' % version)
     # We wrap cg1packer.revchunk, using a side channel to pass
     # relevant_nodes into that area. Then if linknode isn't in the
     # set, we know we have an ellipsis node and we should defer
     # sending that node's data. We override close() to detect
     # pending ellipsis nodes and flush them.
     packer = getbundler(version, repo, filematcher=match)
     # Give the packer the list of nodes which should not be
     # ellipsis nodes. We store this rather than the set of nodes
     # that should be an ellipsis because for very large histories
     # we expect this to be significantly smaller.
     packer.full_nodes = relevant_nodes
     # Maps ellipsis revs to their roots at the changelog level.
     packer.precomputed_ellipsis = ellipsisroots
     # Maps CL revs to per-revlog revisions. Cleared in close() at
     # the end of each group.
     packer.clrev_to_localrev = {}
     packer.next_clrev_to_localrev = {}
     # Maps changelog nodes to changelog revs. Filled in once
     # during changelog stage and then left unmodified.
     packer.clnode_to_rev = {}
     packer.changelog_done = False
     # If true, informs the packer that it is serving shallow content and might
     # need to pack file contents not introduced by the changes being packed.
     packer.is_shallow = depth is not None
 
     return packer.generate(common, visitnodes, False, source)