--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hgext/narrow/narrowdirstate.py	Mon Jan 29 16:19:33 2018 -0500
@@ -0,0 +1,80 @@
+# narrowdirstate.py - extensions to mercurial dirstate to support narrow clones
+#
+# Copyright 2017 Google, Inc.
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+from __future__ import absolute_import
+
+from mercurial.i18n import _
+from mercurial import (
+    dirstate,
+    error,
+    extensions,
+    match as matchmod,
+    util as hgutil,
+)
+
+from . import narrowspec
+
+def setup(repo):
+    """Add narrow spec dirstate ignore, block changes outside narrow spec."""
+
+    def walk(orig, self, match, subrepos, unknown, ignored, full=True,
+             narrowonly=True):
+        if narrowonly:
+            narrowmatch = repo.narrowmatch()
+            match = matchmod.intersectmatchers(match, narrowmatch)
+        return orig(self, match, subrepos, unknown, ignored, full)
+
+    extensions.wrapfunction(dirstate.dirstate, 'walk', walk)
+
+    # Prevent adding files that are outside the sparse checkout
+    editfuncs = ['normal', 'add', 'normallookup', 'copy', 'remove', 'merge']
+    for func in editfuncs:
+        def _wrapper(orig, self, *args):
+            dirstate = repo.dirstate
+            narrowmatch = repo.narrowmatch()
+            for f in args:
+                if f is not None and not narrowmatch(f) and f not in dirstate:
+                    raise error.Abort(_("cannot track '%s' - it is outside " +
+                        "the narrow clone") % f)
+            return orig(self, *args)
+        extensions.wrapfunction(dirstate.dirstate, func, _wrapper)
+
+    def filterrebuild(orig, self, parent, allfiles, changedfiles=None):
+        if changedfiles is None:
+            # Rebuilding entire dirstate, let's filter allfiles to match the
+            # narrowspec.
+            allfiles = [f for f in allfiles if repo.narrowmatch()(f)]
+        orig(self, parent, allfiles, changedfiles)
+
+    extensions.wrapfunction(dirstate.dirstate, 'rebuild', filterrebuild)
+
+    def _narrowbackupname(backupname):
+        assert 'dirstate' in backupname
+        return backupname.replace('dirstate', narrowspec.FILENAME)
+
+    def restorebackup(orig, self, tr, backupname):
+        self._opener.rename(_narrowbackupname(backupname), narrowspec.FILENAME,
+                            checkambig=True)
+        orig(self, tr, backupname)
+
+    extensions.wrapfunction(dirstate.dirstate, 'restorebackup', restorebackup)
+
+    def savebackup(orig, self, tr, backupname):
+        orig(self, tr, backupname)
+
+        narrowbackupname = _narrowbackupname(backupname)
+        self._opener.tryunlink(narrowbackupname)
+        hgutil.copyfile(self._opener.join(narrowspec.FILENAME),
+                        self._opener.join(narrowbackupname), hardlink=True)
+
+    extensions.wrapfunction(dirstate.dirstate, 'savebackup', savebackup)
+
+    def clearbackup(orig, self, tr, backupname):
+        orig(self, tr, backupname)
+        self._opener.unlink(_narrowbackupname(backupname))
+
+    extensions.wrapfunction(dirstate.dirstate, 'clearbackup', clearbackup)