Error when diffing json files

When using diffoscope on certain JSON files, the dump of the diff seems to fail. I have found 2 examples of this issue, with different exceptions being raised

I first ran diffoscope using diffoscope file1.json file2.json.

Here's the content of the files:

• file1.json

{"first": {"second": ["third"]}}

• file2.json

{"first": {"second": ["third", "fourth"]}}

And here's the error's traceback:

Traceback (most recent call last):
  File "diffoscope/main.py", line 745, in main
    sys.exit(run_diffoscope(parsed_args))
  File "diffoscope/main.py", line 697, in run_diffoscope
    difference = compare_root_paths(path1, path2)
  File "diffoscope/comparators/utils/compare.py", line 74, in compare_root_paths
    difference = compare_files(file1, file2)
  File "diffoscope/comparators/utils/compare.py", line 128, in compare_files
    return file1.compare(file2, source)
  File "diffoscope/comparators/utils/file.py", line 464, in compare
    difference = self._compare_using_details(other, source)
  File "diffoscope/comparators/utils/file.py", line 382, in _compare_using_details
    details.extend(self.compare_details(other, source))
  File "diffoscope/comparators/json.py", line 59, in compare_details
    self.compare_with_jsondiff(difference, other)
  File "diffoscope/comparators/json.py", line 91, in compare_with_jsondiff
    json.dumps(diff, indent=2, sort_keys=True)
  File "/usr/lib/python3.8/json/__init__.py", line 234, in dumps
    return cls(
  File "/usr/lib/python3.8/json/encoder.py", line 201, in encode
    chunks = list(chunks)
  File "/usr/lib/python3.8/json/encoder.py", line 431, in _iterencode
    yield from _iterencode_dict(o, _current_indent_level)
  File "/usr/lib/python3.8/json/encoder.py", line 405, in _iterencode_dict
    yield from chunks
  File "/usr/lib/python3.8/json/encoder.py", line 405, in _iterencode_dict
    yield from chunks
  File "/usr/lib/python3.8/json/encoder.py", line 376, in _iterencode_dict
    raise TypeError(f'keys must be str, int, float, bool or None, '
TypeError: keys must be str, int, float, bool or None, not Symbol

Here's the second error I found, when running diffoscope lang1.json lang2.json:

Traceback (most recent call last):
  File "diffoscope/main.py", line 745, in main
    sys.exit(run_diffoscope(parsed_args))
  File "diffoscope/main.py", line 697, in run_diffoscope
    difference = compare_root_paths(path1, path2)
  File "diffoscope/comparators/utils/compare.py", line 74, in compare_root_paths
    difference = compare_files(file1, file2)
  File "diffoscope/comparators/utils/compare.py", line 128, in compare_files
    return file1.compare(file2, source)
  File "comparators/utils/file.py", line 464, in compare
    difference = self._compare_using_details(other, source)
  File "diffoscope/comparators/utils/file.py", line 382, in _compare_using_details
    details.extend(self.compare_details(other, source))
  File "diffoscope/comparators/json.py", line 59, in compare_details
    self.compare_with_jsondiff(difference, other)
  File "diffoscope/comparators/json.py", line 91, in compare_with_jsondiff
    json.dumps(diff, indent=2, sort_keys=True)
  File "/usr/lib/python3.8/json/__init__.py", line 234, in dumps
    return cls(
  File "/usr/lib/python3.8/json/encoder.py", line 201, in encode
    chunks = list(chunks)
  File "/usr/lib/python3.8/json/encoder.py", line 431, in _iterencode
    yield from _iterencode_dict(o, _current_indent_level)
  File "/usr/lib/python3.8/json/encoder.py", line 405, in _iterencode_dict
    yield from chunks
  File "/usr/lib/python3.8/json/encoder.py", line 405, in _iterencode_dict
    yield from chunks
  File "/usr/lib/python3.8/json/encoder.py", line 353, in _iterencode_dict
    items = sorted(dct.items())
TypeError: '<' not supported between instances of 'Symbol' and 'Symbol'

I have also attached both files for convenience:

• lang1.json
• lang2.json