Consistent control of caller stack frames output

This commit aims to achieve consistent stack frames control
by `stack_info` flag in logging calls the same as that in python
logging module.
Currently, both a field named `stack_info` for JsonFormatter
and `stack_info=True` for logging function are needed for
stack frames to be properly displayed.
If `stack_info` field name is not passed, no output is given
irrespective of the `stack_info` flag in logging calls.
If `stack_info=False` in logging calls and `stack_info` is also
passed as one field for JsonFormatter, the output is `{"stack_info": null}`.
Above behavior is not very consistent and requires two controls
to output stack frames. This commit makes 'stack_info' flag in logging calls
as single point control of stack frames output and there is no need to
pass `stack_info` field into JsonFormatter.

Author: ghShu

src/pythonjsonlogger/jsonlogger.py

@@ -77,7 +77,7 @@ def format_datetime_obj(self, obj):
 class JsonFormatter(logging.Formatter):
     """
     A custom formatter to format logging records as json strings.
-    extra values will be formatted as str() if nor supported by
+    Extra values will be formatted as str() if not supported by
     json default encoder
     """
 
@@ -193,6 +193,10 @@ def format(self, record):
             message_dict['exc_info'] = self.formatException(record.exc_info)
         if not message_dict.get('exc_info') and record.exc_text:
             message_dict['exc_info'] = record.exc_text
+        # Display formatted record of stack frames
+        # default format is a string returned from :func:`traceback.print_stack`
+        if record.stack_info and not message_dict.get('stack_info'):
+            message_dict['stack_info'] = self.formatStack(record.stack_info)
 
         try:
             log_record = OrderedDict()