Fixed #25468 -- Made DjangoJSONEncoder lazy string aware

Thanks Stavros Korokithakis for the report and Tim Graham for the
review.

django/core/serializers/json.py

@@ -16,6 +16,7 @@ from django.core.serializers.python import (
     Deserializer as PythonDeserializer, Serializer as PythonSerializer,
 )
 from django.utils import six
+from django.utils.functional import Promise
 from django.utils.timezone import is_aware
 
 
@@ -111,6 +112,8 @@ class DjangoJSONEncoder(json.JSONEncoder):
             return str(o)
         elif isinstance(o, uuid.UUID):
             return str(o)
+        elif isinstance(o, Promise):
+            return six.text_type(o)
         else:
             return super(DjangoJSONEncoder, self).default(o)
 

docs/releases/1.10.txt

@@ -162,6 +162,12 @@ Requests and Responses
 
 * ...
 
+Serialization
+^^^^^^^^^^^^^
+
+* The ``django.core.serializers.json.DjangoJSONEncoder`` now knows how to
+  serialize lazy strings, typically used for translatable content.
+
 Signals
 ^^^^^^^
 

docs/topics/serialization.txt

@@ -256,16 +256,15 @@ Date and datetime related types are treated in a special way by the JSON
 serializer to make the format compatible with `ECMA-262`_.
 
 Be aware that not all Django output can be passed unmodified to :mod:`json`.
-In particular, :ref:`lazy translation objects <lazy-translations>` need a
-`special encoder`_ written for them. Something like this will work::
+For example, if you have some custom type in an object to be serialized, you'll
+have to write a `special encoder`_ for it. Something like this will work::
 
-    from django.utils.functional import Promise
     from django.utils.encoding import force_text
     from django.core.serializers.json import DjangoJSONEncoder
 
     class LazyEncoder(DjangoJSONEncoder):
         def default(self, obj):
-            if isinstance(obj, Promise):
+            if isinstance(obj, YourCustomType):
                 return force_text(obj)
             return super(LazyEncoder, self).default(obj)
 

tests/serializers/test_json.py

@@ -6,7 +6,9 @@ import re
 
 from django.core import serializers
 from django.core.serializers.base import DeserializationError
-from django.test import TestCase, TransactionTestCase
+from django.core.serializers.json import DjangoJSONEncoder
+from django.test import SimpleTestCase, TestCase, TransactionTestCase
+from django.utils.translation import override, ugettext_lazy
 
 from .models import Score
 from .tests import SerializersTestBase, SerializersTransactionTestBase
@@ -271,3 +273,16 @@ class JsonSerializerTransactionTestCase(SerializersTransactionTestBase, Transact
             "name": "Agnes"
         }
     }]"""
+
+
+class DjangoJSONEncoderTests(SimpleTestCase):
+    def test_lazy_string_encoding(self):
+        self.assertEqual(
+            json.dumps({'lang': ugettext_lazy("French")}, cls=DjangoJSONEncoder),
+            '{"lang": "French"}'
+        )
+        with override('fr'):
+            self.assertEqual(
+                json.dumps({'lang': ugettext_lazy("French")}, cls=DjangoJSONEncoder),
+                '{"lang": "Fran\\u00e7ais"}'
+            )