always update to the correct head of Mercurial repositories (#4600)

use the head on given branch with maximum index

Author: vladak

tools/src/main/python/opengrok_tools/scm/mercurial.py

@@ -18,7 +18,7 @@
 #
 
 #
-# Copyright (c) 2018, 2021, Oracle and/or its affiliates. All rights reserved.
+# Copyright (c) 2018, 2024, Oracle and/or its affiliates. All rights reserved.
 # Portions Copyright (c) 2020, Krystof Tulinger <k.tulinger@seznam.cz>
 #
 
@@ -78,10 +78,20 @@ def reposync(self):
             return 1
 
         hg_command = [self.command, "update"]
+        #
         # Avoid remote branch lookup for default branches since
         # some servers do not support it.
+        #
         if branch == "default":
             hg_command.append("--check")
+
+        #
+        # In a multi-head situation, select the head with the
+        # biggest index as this is likely the correct one.
+        #
+        hg_command.append("-r")
+        hg_command.append("'max(head() and branch(\".\"))'")
+
         cmd = self.get_command(hg_command, work_dir=self.path,
                                env_vars=self.env, logger=self.logger)
         cmd.execute()