[PATCH 5 of 5] rank: compute property incrementally

[pacien]

# HG changeset patch
# User pacien <pacien.trangirard at pacien.net>
# Date 1643367284 -3600
#      Fri Jan 28 11:54:44 2022 +0100
# Node ID 13b044b7e39299156aac33e68550b7004ad21cba
# Parent  04b7286cc3c4c7e332294183cfb87366d9748ca6
# EXP-Topic cl2-rank
rank: compute property incrementally

This replace the naive rank computation with more efficient incremental
method, avoiding computing the whole ancestor set when possible.

diff --git a/mercurial/revlog.py b/mercurial/revlog.py
--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -2491,7 +2491,17 @@
         # maybe the index.append should compute it when applicable instead
         rank = RANK_UNKNOWN
         if self._format_version == CHANGELOGV2:
-            rank = len(list(self.ancestors([p1r, p2r], inclusive=True))) + 1
+            if (p1r, p2r) == (nullrev, nullrev):
+                rank = 1
+            elif p1r != nullrev and p2r == nullrev:
+                rank = 1 + self.fast_rank(p1r)
+            elif p1r == nullrev and p2r != nullrev:
+                rank = 1 + self.fast_rank(p2r)
+            else:  # merge node
+                # TODO: use exclusive part size from leap info when those will
+                #       be available
+                rank = (1 +
+                  sum(1 for _ in self.ancestors([p1r, p2r], inclusive=True)))
 
         e = revlogutils.entry(
             flags=flags,