[PATCH] changegroup: allow sending snapshot deltas in cg2

[Mike Edgar]

# HG changeset patch
# User Mike Edgar <adgar at google.com>
# Date 1416610038 18000
#      Fri Nov 21 17:47:18 2014 -0500
# Node ID ce1d4cdad3e2a324198a348f5a62f86e9b0e1a73
# Parent  a179db3db9b96b38c10c491e6e7e7ad5f40a7787
changegroup: allow sending snapshot deltas in cg2

The changegroup2 format allows each revision to be sent with
a configurable base. That base is presently restricted to
p1, p2, or the previous revision in the revlog. By allowing
a null base, we can send snapshot deltas when it is efficient
to do so.

diff -r a179db3db9b9 -r ce1d4cdad3e2 mercurial/changegroup.py
--- a/mercurial/changegroup.py	Wed Nov 19 23:15:07 2014 -0800
+++ b/mercurial/changegroup.py	Fri Nov 21 17:47:18 2014 -0500
@@ -455,9 +455,9 @@
 
     def deltaparent(self, revlog, rev, p1, p2, prev):
         dp = revlog.deltaparent(rev)
-        # avoid storing full revisions; pick prev in those cases
-        # also pick prev when we can't be sure remote has dp
-        if dp == nullrev or (dp != p1 and dp != p2 and dp != prev):
+        # if revlog delta base is null, send a snapshot, no known good base.
+        # otherwise, pick prev when we can't be sure remote has dp
+        if dp != nullrev and dp != p1 and dp != p2 and dp != prev:
             return prev
         return dp