Fixed #25875 -- Prevented UnicodeDecodeError for Q object repr

Thanks Ben Kraft for the report, and Simon Charette for the review.

django/utils/tree.py

@@ -5,6 +5,8 @@ ORM.
 
 import copy
 
+from django.utils.encoding import force_str, force_text
+
 
 class Node(object):
     """
@@ -42,14 +44,11 @@ class Node(object):
         return obj
 
     def __str__(self):
-        if self.negated:
-            return '(NOT (%s: %s))' % (self.connector, ', '.join(str(c) for c
-                    in self.children))
-        return '(%s: %s)' % (self.connector, ', '.join(str(c) for c in
-                self.children))
+        template = '(NOT (%s: %s))' if self.negated else '(%s: %s)'
+        return force_str(template % (self.connector, ', '.join(force_text(c) for c in self.children)))
 
     def __repr__(self):
-        return "<%s: %s>" % (self.__class__.__name__, self)
+        return str("<%s: %s>") % (self.__class__.__name__, self)
 
     def __deepcopy__(self, memodict):
         """

tests/or_lookups/tests.py

+# -*- encoding: utf-8 -*-
 from __future__ import unicode_literals
 
 from datetime import datetime
@@ -5,6 +6,7 @@ from operator import attrgetter
 
 from django.db.models import Q
 from django.test import TestCase
+from django.utils.encoding import force_str
 
 from .models import Article
 
@@ -123,6 +125,12 @@ class OrLookupsTests(TestCase):
             attrgetter("headline"),
         )
 
+    def test_q_repr(self):
+        or_expr = Q(baz=Article(headline="Foö"))
+        self.assertEqual(repr(or_expr), force_str("<Q: (AND: ('baz', <Article: Foö>))>"))
+        negated_or = ~Q(baz=Article(headline="Foö"))
+        self.assertEqual(repr(negated_or), force_str("<Q: (NOT (AND: ('baz', <Article: Foö>)))>"))
+
     def test_q_negated(self):
         # Q objects can be negated
         self.assertQuerysetEqual(