Fixed #20812 -- Error out if __unicode__/__str__ doesn't return a text type.

django/utils/encoding.py

@@ -67,14 +67,13 @@ def force_text(s, encoding='utf-8', strings_only=False, errors='strict'):
         return s
     try:
         if not isinstance(s, six.string_types):
-            if hasattr(s, '__unicode__'):
-                s = s.__unicode__()
-            else:
             if six.PY3:
                 if isinstance(s, bytes):
                     s = six.text_type(s, encoding, errors)
                 else:
                     s = six.text_type(s)
+            elif hasattr(s, '__unicode__'):
+                s = six.text_type(s)
             else:
                 s = six.text_type(bytes(s), encoding, errors)
         else:

tests/utils_tests/test_encoding.py

@@ -4,10 +4,25 @@ from __future__ import unicode_literals
 import unittest
 import datetime
 
-from django.utils.encoding import force_bytes, filepath_to_uri
+from django.utils import six
+from django.utils.encoding import force_bytes, force_text, filepath_to_uri
 
 
 class TestEncodingUtils(unittest.TestCase):
+    def test_force_text_exception(self):
+        """
+        Check that broken __unicode__/__str__ actually raises an error.
+        """
+        class MyString(object):
+            def __str__(self):
+                return b'\xc3\xb6\xc3\xa4\xc3\xbc'
+
+            __unicode__ = __str__
+
+        # str(s) raises a TypeError on python 3 if the result is not a text type.
+        # python 2 fails when it tries converting from str to unicode (via ASCII).
+        exception = TypeError if six.PY3 else UnicodeError
+        self.assertRaises(exception, force_text, MyString())
 
     def test_force_bytes_exception(self):
         """