# HG changeset patch
# User Mads Kiilerich <madski@unity3d.com>
# Date 1408403590 -7200
# Node ID 392ae5cb8d62b8c2f26346a4977170211adb3822
# Parent  82b2ba904e3ec0668760c0cefd5ced87b533b45d
revlog: introduce isancestor method for efficiently determining node lineage

Hide the not so obvious use of commonancestorsheads.

diff -r 82b2ba904e3e -r 392ae5cb8d62 mercurial/commands.py
--- a/mercurial/commands.py	Tue Sep 09 17:16:24 2014 -0400
+++ b/mercurial/commands.py	Tue Aug 19 01:13:10 2014 +0200
@@ -454,7 +454,7 @@
     node = scmutil.revsingle(repo, rev).node()
 
     op1, op2 = repo.dirstate.parents()
-    if node not in repo.changelog.commonancestorsheads(op1, node):
+    if not repo.changelog.isancestor(node, op1):
         raise util.Abort(_('cannot backout change that is not an ancestor'))
 
     p1, p2 = repo.changelog.parents(node)
diff -r 82b2ba904e3e -r 392ae5cb8d62 mercurial/revlog.py
--- a/mercurial/revlog.py	Tue Sep 09 17:16:24 2014 -0400
+++ b/mercurial/revlog.py	Tue Aug 19 01:13:10 2014 +0200
@@ -745,6 +745,13 @@
             ancs = ancestor.commonancestorsheads(self.parentrevs, a, b)
         return map(self.node, ancs)
 
+    def isancestor(self, a, b):
+        """return True if node a is an ancestor of node b
+
+        The implementation of this is trivial but the use of
+        commonancestorsheads is not."""
+        return a in self.commonancestorsheads(a, b)
+
     def ancestor(self, a, b):
         """calculate the least common ancestor of nodes a and b"""