diff -r a3a36bcf122e -r 1858fc2327ef mercurial/obsutil.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mercurial/obsutil.py	Thu Jun 15 13:02:58 2017 +0200
@@ -0,0 +1,36 @@
+# obsutil.py - utility functions for obsolescence
+#
+# Copyright 2017 Boris Feld <boris.feld@octobus.net>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+from __future__ import absolute_import
+
+def closestpredecessors(repo, nodeid):
+    """yield the list of next predecessors pointing on visible changectx nodes
+
+    This function respect the repoview filtering, filtered revision will be
+    considered missing.
+    """
+
+    precursors = repo.obsstore.precursors
+    stack = [nodeid]
+    seen = set(stack)
+
+    while stack:
+        current = stack.pop()
+        currentpreccs = precursors.get(current, ())
+
+        for prec in currentpreccs:
+            precnodeid = prec[0]
+
+            # Basic cycle protection
+            if precnodeid in seen:
+                continue
+            seen.add(precnodeid)
+
+            if precnodeid in repo:
+                yield precnodeid
+            else:
+                stack.append(precnodeid)