PB-931 Fix stack_info formatting in JSON formatter

Add the stack info to the record instead of the message directly in JSON
formatter. This way it can be configured through the Django logging
facility

logging_utilities/formatters/json_formatter.py

@@ -349,14 +349,14 @@ def format(self, record):
             if not record.exc_text:
                 record.exc_text = self.formatException(record.exc_info)
 
+        if record.stack_info:
+            record.stack_info = self.formatStack(record.stack_info)
+
         message = self.formatMessage(record)
 
         if self.add_always_extra:
             self._add_extra_to_message(extra, message)
 
-        if record.stack_info:
-            message['stack_info'] = self.formatStack(record.stack_info)
-
         # When adding all extras, to avoid crash when a log message adds an extra with a non
         # serializable object, we add a default serializer.
         default = self.kwargs.pop('default', None)

tests/test_json_formatter.py

@@ -378,11 +378,8 @@ def test_stack_info(self):
             logger = logging.getLogger('test_formatter')
             self._configure_logger(
                 logger,
-                fmt=dictionary([
-                    ('levelname', 'levelname'),
-                    ('name', 'name'),
-                    ('message', 'message'),
-                ])
+                fmt=dictionary([('levelname', 'levelname'), ('name', 'name'),
+                                ('message', 'message'), ('stack_info', 'stack_info')])
             )
             logger.info('Message with stack info', stack_info=True)
         message = json.loads(ctx.output[0], object_pairs_hook=dictionary)