diff -r fabf687df0ff -r e2da3ec94169 mercurial/pure/parsers.py
--- a/mercurial/pure/parsers.py	Wed Sep 29 01:23:10 2021 +0200
+++ b/mercurial/pure/parsers.py	Thu Sep 30 18:07:31 2021 +0200
@@ -102,6 +102,7 @@
             msg = b'`merged` argument incompatible with `clean_p1`/`clean_p2`'
             raise error.ProgrammingError(msg)
 
+        assert not (merged and not p1_tracked)
         self._wc_tracked = wc_tracked
         self._p1_tracked = p1_tracked
         self._p2_tracked = p2_tracked