# HG changeset patch
# User Pierre-Yves David <pierre-yves.david@fb.com>
# Date 2014-08-26 09:36:23
# Node ID cf7014c5f087afb15bac1bcc5186eb15f117a451
# Parent  9829b79481000b3f6f1242959a15a5bf78e56023

obsolete: add a `commonversion` function

This function returns the highest common version between the locally known
formats and a list of remotely known formats. This is going to be useful to
know what format should be used for exchange.

diff --git a/mercurial/obsolete.py b/mercurial/obsolete.py
--- a/mercurial/obsolete.py
+++ b/mercurial/obsolete.py
@@ -455,6 +455,17 @@ class obsstore(object):
             seennodes |= pendingnodes
         return seenmarkers
 
+def commonversion(versions):
+    """Return the newest version listed in both versions and our local formats.
+
+    Returns None if no common version exists.
+    """
+    versions.sort(reverse=True)
+    # search for highest version known on both side
+    for v in versions:
+        if v in formats:
+            return v
+    return None
 
 # arbitrary picked to fit into 8K limit from HTTP server
 # you have to take in account: