When I accidentally put a Path() into updtodate, I get this stack trace:

Traceback (most recent call last):
  File "doit-0.32.0/lib/python3.7/site-packages/doit/doit_cmd.py", line 190, in run
    return command.parse_execute(args)
  File "doit-0.32.0/lib/python3.7/site-packages/doit/cmd_base.py", line 150, in parse_execute
    return self.execute(params, args)
  File "doit-0.32.0/lib/python3.7/site-packages/doit/cmd_base.py", line 601, in execute
    return self._execute(**exec_params)
  File "doit-0.32.0/lib/python3.7/site-packages/doit/cmd_run.py", line 264, in _execute
    return runner.run_all(self.control.task_dispatcher())
  File "doit-0.32.0/lib/python3.7/site-packages/doit/runner.py", line 256, in run_all
    self.run_tasks(task_dispatcher)
  File "doit-0.32.0/lib/python3.7/site-packages/doit/runner.py", line 219, in run_tasks
    if not self.select_task(node, task_dispatcher.tasks):
  File "doit-0.32.0/lib/python3.7/site-packages/doit/runner.py", line 131, in select_task
    res = self.dep_manager.get_status(task, tasks_dict)
  File "doit-0.32.0/lib/python3.7/site-packages/doit/dependency.py", line 630, in get_status
    uptodate_result = utd(*args, **utd_kwargs)
  File "doit-0.32.0/lib/python3.7/site-packages/doit/tools.py", line 74, in __call__
    self.config_digest = self._calc_digest()
  File "doit-0.32.0/lib/python3.7/site-packages/doit/tools.py", line 62, in _calc_digest
    data = json.dumps(self.config, sort_keys=True, cls=self.encoder)
  File "python3-3.7.6/lib/python3.7/json/__init__.py", line 238, in dumps
    **kw).encode(obj)
  File "python3-3.7.6/lib/python3.7/json/encoder.py", line 199, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "python3-3.7.6/lib/python3.7/json/encoder.py", line 257, in iterencode
    return _iterencode(o, 0)
  File "python3-3.7.6/lib/python3.7/json/encoder.py", line 179, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type PosixPath is not JSON serializable

This is difficult to debug for large doit projects, because it only tells me that "something somewhere is not JSON serializable".

It would be great if doit could tell me which task, and even better, which key in the object.

I suspect this could be done by catching the JSON encoding error around here:

and augmenting its error message with the task name.

Environment

1. OS: NixOS 20.03
2. python version: 3.7.6
3. doit version: 0.32.0