`save_workgraph_data` fails on non-JSON-serializable default values in `@task.graph` function signatures

[elinscott]

Having implemented a custom serlaizer for Enum i.e.

[project.entry-points."aiida.data"]
"koopmans.aiida_quantumespresso.common.types.ElectronicType" = "aiida.orm.nodes.data.enum:EnumData"

the serialization does not carry over to save_workgraph_data. Specifically, when a @task.graph-decorated function has parameters with non-JSON-serializable defaults (e.g. Enum members), save_workgraph_data fails because it stores the full graph definition — including these defaults — as a node attribute via node.workgraph_data = wgdata, which triggers clean_value().

  File "/home/linsco_e/code/koopmans2/.venv/lib/python3.13/site-packages/aiida_workgraph/engine/workgraph.py", line 254, in on_create
    save_workgraph_data(self.node, raw_inputs)
    ~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/linsco_e/code/koopmans2/.venv/lib/python3.13/site-packages/aiida_workgraph/utils/__init__.py", line 228, in save_workgraph_data
    node.workgraph_data = wgdata
    ^^^^^^^^^^^^^^^^^^^
  File "/home/linsco_e/code/koopmans2/.venv/lib/python3.13/site-packages/aiida_workgraph/orm/workgraph.py", line 24, in setter
    self.base.attributes.set(attribute_key, value)
    ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^
  File "/home/linsco_e/code/koopmans2/.venv/lib/python3.13/site-packages/aiida/orm/nodes/attributes.py", line 119, in set
    self._backend_node.set_attribute(key, value)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^
  File "/home/linsco_e/code/koopmans2/.venv/lib/python3.13/site-packages/aiida/storage/psql_dos/orm/nodes.py", line 248, in set_attribute
    value = clean_value(value)
  File "/home/linsco_e/code/koopmans2/.venv/lib/python3.13/site-packages/aiida/orm/implementation/utils.py", line 102, in clean_value
    return {k: clean_value(v) for k, v in value.items()}
               ~~~~~~~~~~~^^^
  File "/home/linsco_e/code/koopmans2/.venv/lib/python3.13/site-packages/aiida/orm/implementation/utils.py", line 102, in clean_value
    return {k: clean_value(v) for k, v in value.items()}
               ~~~~~~~~~~~^^^
  File "/home/linsco_e/code/koopmans2/.venv/lib/python3.13/site-packages/aiida/orm/implementation/utils.py", line 102, in clean_value
    return {k: clean_value(v) for k, v in value.items()}
               ~~~~~~~~~~~^^^
  [Previous line repeated 2 more times]
  File "/home/linsco_e/code/koopmans2/.venv/lib/python3.13/site-packages/aiida/orm/implementation/utils.py", line 115, in clean_value
    return clean_builtin(value)
  File "/home/linsco_e/code/koopmans2/.venv/lib/python3.13/site-packages/aiida/orm/implementation/utils.py", line 95, in clean_builtin
    raise exceptions.ValidationError(f'type `{type(val)}` is not supported as it is not json-serializable')
aiida.common.exceptions.ValidationError: type `<enum 'ElectronicType'>` is not supported as it is not json-serializable
...
aiida/orm/implementation/utils.py:95     clean_builtin
  raise ValidationError(f'type `{type(val)}` is not supported as it is not json-serializable')

ValidationError: type `<enum 'ElectronicType'>` is not supported as it is not json-serializable

Is this a bug? Or have I not implemented the custom serializer correctly? We clearly want to be able to provide Enum members as defaults somehow...

[elinscott]

@edan-bainglass @superstar54

[elinscott]

The following quick-and-dirty patch fixes the issue

    node.workgraph_data = _ensure_json_safe(wgdata)
    node.workgraph_data_short = _ensure_json_safe(short_wgdata)
    node.workgraph_error_handlers = _ensure_json_safe(wgdata.pop('error_handlers', {}))

where

def _ensure_json_safe(value: Any) -> Any:
    """Recursively ensure all values in a nested structure are JSON-serializable.

    Node attributes must be JSON-serializable.  Workgraph data may contain
    non-serializable Python objects (e.g. enum defaults from task function
    signatures).  This function converts them to safe representations.
    """
    if value is None or isinstance(value, (bool, int, float, str)):
        return value
    if isinstance(value, dict):
        return {k: _ensure_json_safe(v) for k, v in value.items()}
    if isinstance(value, (list, tuple)):
        return [_ensure_json_safe(v) for v in value]
    try:
        json.dumps(value)
        return value
    except (TypeError, ValueError):
        pass
    # Unwrap value-like objects (enums, etc.)
    if hasattr(value, 'value') and not callable(value.value):
        return _ensure_json_safe(value.value)
    return str(value)

but I'm not sure this really deals with the root cause.