--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/contrib/dirstatenonnormalcheck.py	Mon Dec 21 16:26:44 2015 -0800
@@ -0,0 +1,57 @@
+# dirstatenonnormalcheck.py - extension to check the consistency of the
+# dirstate's non-normal map
+#
+# For most operations on dirstate, this extensions checks that the nonnormalset
+# contains the right entries.
+# It compares the nonnormal file to a nonnormalset built from the map of all
+# the files in the dirstate to check that they contain the same files.
+
+from __future__ import absolute_import
+
+from mercurial import (
+    dirstate,
+    extensions,
+)
+
+def nonnormalentries(dmap):
+    """Compute nonnormal entries from dirstate's dmap"""
+    res = set()
+    for f, e in dmap.iteritems():
+        if e[0] != 'n' or e[3] == -1:
+            res.add(f)
+    return res
+
+def checkconsistency(ui, orig, dmap, _nonnormalset, label):
+    """Compute nonnormalset from dmap, check that it matches _nonnormalset"""
+    nonnormalcomputedmap = nonnormalentries(dmap)
+    if _nonnormalset != nonnormalcomputedmap:
+        ui.develwarn("%s call to %s\n" % (label, orig))
+        ui.develwarn("inconsistency in nonnormalset\n")
+        ui.develwarn("[nonnormalset] %s\n" % _nonnormalset)
+        ui.develwarn("[map] %s\n" % nonnormalcomputedmap)
+
+def _checkdirstate(orig, self, arg):
+    """Check nonnormal set consistency before and after the call to orig"""
+    checkconsistency(self._ui, orig, self._map, self._nonnormalset, "before")
+    r =  orig(self, arg)
+    checkconsistency(self._ui, orig, self._map, self._nonnormalset, "after")
+    return r
+
+def extsetup(ui):
+    """Wrap functions modifying dirstate to check nonnormalset consistency"""
+    dirstatecl = dirstate.dirstate
+    devel = ui.configbool('devel', 'all-warnings')
+    paranoid = ui.configbool('experimental', 'nonnormalparanoidcheck')
+    if devel:
+        extensions.wrapfunction(dirstatecl, '_writedirstate', _checkdirstate)
+        if paranoid:
+            # We don't do all these checks when paranoid is disable as it would
+            # make the extension run very slowly on large repos
+            extensions.wrapfunction(dirstatecl, 'normallookup', _checkdirstate)
+            extensions.wrapfunction(dirstatecl, 'otherparent', _checkdirstate)
+            extensions.wrapfunction(dirstatecl, 'normal', _checkdirstate)
+            extensions.wrapfunction(dirstatecl, 'write', _checkdirstate)
+            extensions.wrapfunction(dirstatecl, 'add', _checkdirstate)
+            extensions.wrapfunction(dirstatecl, 'remove', _checkdirstate)
+            extensions.wrapfunction(dirstatecl, 'merge', _checkdirstate)
+            extensions.wrapfunction(dirstatecl, 'drop', _checkdirstate)