[PATCH 1 of 3 RFC] changegroup: add a "packermap" dictionary to track different packer version

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at fb.com>
# Date 1411619046 25200
#      Wed Sep 24 21:24:06 2014 -0700
# Node ID 7850f829f2b1a731653c96e78a5acc10300d02a3
# Parent  a24f96a788b3e94a8c93dc259839728a38c2446a
changegroup: add a "packermap" dictionary to track different packer version

We only have one right now (HG10) but we should get general delta in soon.
Bundle2 is expected to make use of this to advertise and select the right packer
to use on both side.

diff --git a/mercurial/changegroup.py b/mercurial/changegroup.py
--- a/mercurial/changegroup.py
+++ b/mercurial/changegroup.py
@@ -431,10 +431,12 @@ class cg1packer(object):
         yield delta
     def builddeltaheader(self, node, p1n, p2n, basenode, linknode):
         # do nothing with basenode, it is implicitly the previous one in HG10
         return struct.pack(self.deltaheader, node, p1n, p2n, linknode)
 
+packermap = {'HG10': (cg1packer, cg1unpacker)}
+
 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")