[PATCH] dagop: raise ProgrammingError if stopdepth<=0

[Martin von Zweigbergk]

# HG changeset patch
# User Martin von Zweigbergk <martinvonz at google.com>
# Date 1498281322 25200
#      Fri Jun 23 22:15:22 2017 -0700
# Node ID d654eefeefdd3df493fa777cbcfe423f17d9d500
# Parent  fac9941bd542e3621082b157fb2f3aff09cfb1b7
dagop: raise ProgrammingError if stopdepth<=0

revset.py should never send such a value.

diff --git a/mercurial/dagop.py b/mercurial/dagop.py
--- a/mercurial/dagop.py
+++ b/mercurial/dagop.py
@@ -33,7 +33,7 @@
     if stopdepth is None:
         stopdepth = _maxlogdepth
     if stopdepth <= 0:
-        return
+        raise error.ProgrammingError('negative stopdepth')
 
     cl = repo.changelog