diff mercurial/revlogutils/deltas.py @ 39520:5aef5afa8654

snapshot: refine candidate snapshot base upward

Once we found a suitable snapshot base it is useful to check if it has a
"children" snapshot that would provide a better diff. This is useful when base
not directly related to stored revision are picked. In those case, we "jumped"
to this new chain at an arbitrary point, checking if a higher point is more
appropriate will help to provide better results and increase snapshot reuse.

--- a/mercurial/revlogutils/deltas.py	Fri Sep 07 11:17:35 2018 -0400
+++ b/mercurial/revlogutils/deltas.py	Fri Sep 07 11:17:36 2018 -0400
@@ -658,6 +658,19 @@
             if base == nullrev:
                 break
             good = yield (base,)
+        # refine snapshot up
+        #
+        # XXX the _findsnapshots call can be expensive and is "duplicated" with
+        # the one done in `_rawgroups`. Once we start working on performance,
+        # we should make the two logics share this computation.
+        snapshots = collections.defaultdict(list)
+        _findsnapshots(revlog, snapshots, good + 1)
+        previous = None
+        while good != previous:
+            previous = good
+            children = tuple(sorted(c for c in snapshots[good]))
+            good = yield children
+
     # we have found nothing
     yield None