--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hgext/narrow/narrowpatch.py	Mon Jan 29 16:19:33 2018 -0500
@@ -0,0 +1,42 @@
+# narrowpatch.py - extensions to mercurial patch module 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 import (
+    extensions,
+    patch,
+    util,
+)
+
+def setup(repo):
+    def _filepairs(orig, *args):
+        """Only includes files within the narrow spec in the diff."""
+        if util.safehasattr(repo, 'narrowmatch'):
+            narrowmatch = repo.narrowmatch()
+            for x in orig(*args):
+                f1, f2, copyop = x
+                if ((not f1 or narrowmatch(f1)) and
+                    (not f2 or narrowmatch(f2))):
+                    yield x
+        else:
+            for x in orig(*args):
+                yield x
+
+    def trydiff(orig, repo, revs, ctx1, ctx2, modified, added, removed,
+                copy, getfilectx, *args, **kwargs):
+        if util.safehasattr(repo, 'narrowmatch'):
+            narrowmatch = repo.narrowmatch()
+            modified = filter(narrowmatch, modified)
+            added = filter(narrowmatch, added)
+            removed = filter(narrowmatch, removed)
+            copy = {k: v for k, v in copy.iteritems() if narrowmatch(k)}
+        return orig(repo, revs, ctx1, ctx2, modified, added, removed, copy,
+                    getfilectx, *args, **kwargs)
+
+    extensions.wrapfunction(patch, '_filepairs', _filepairs)
+    extensions.wrapfunction(patch, 'trydiff', trydiff)