diff -r cd2aca0808f8 -r f5fc54e7e467 mercurial/pure/charencode.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mercurial/pure/charencode.py	Mon Jul 31 23:13:47 2017 +0900
@@ -0,0 +1,22 @@
+# charencode.py - miscellaneous character encoding
+#
+#  Copyright 2005-2009 Matt Mackall <mpm@selenic.com> and others
+#
+# 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
+
+def asciilower(s):
+    '''convert a string to lowercase if ASCII
+
+    Raises UnicodeDecodeError if non-ASCII characters are found.'''
+    s.decode('ascii')
+    return s.lower()
+
+def asciiupper(s):
+    '''convert a string to uppercase if ASCII
+
+    Raises UnicodeDecodeError if non-ASCII characters are found.'''
+    s.decode('ascii')
+    return s.upper()