Stop JSONBoundField mangling invalid JSON (#5526)

rest_framework/utils/serializer_helpers.py

@@ -86,10 +86,13 @@ def as_form_field(self):
 class JSONBoundField(BoundField):
     def as_form_field(self):
         value = self.value
-        try:
-            value = json.dumps(self.value, sort_keys=True, indent=4)
-        except (TypeError, ValueError):
-            pass
+        # When HTML form input is used and the input is not valid
+        # value will be a JSONString, rather than a JSON primitive.
+        if not getattr(value, 'is_json_string', False):
+            try:
+                value = json.dumps(self.value, sort_keys=True, indent=4)
+            except (TypeError, ValueError):
+                pass
         return self.__class__(self._field, value, self.errors, self._prefix)
 
 

tests/test_bound_fields.py

@@ -1,3 +1,5 @@
+from django.http import QueryDict
+
 from rest_framework import serializers
 
 
@@ -160,3 +162,15 @@ class ExampleSerializer(serializers.Serializer):
             )
             rendered_packed = ''.join(rendered.split())
             assert rendered_packed == expected_packed
+
+
+class TestJSONBoundField:
+    def test_as_form_fields(self):
+        class TestSerializer(serializers.Serializer):
+            json_field = serializers.JSONField()
+
+        data = QueryDict(mutable=True)
+        data.update({'json_field': '{"some": ["json"}'})
+        serializer = TestSerializer(data=data)
+        assert serializer.is_valid() is False
+        assert serializer['json_field'].as_form_field().value == '{"some": ["json"}'