🐛 Do not require the children of an omitted optional namespace

[elinscott]

Problem

An optional namespace input cannot be omitted. If a task declares a grouped input that may be left out entirely — a TypedDict | None parameter, for instance — check_before_run() wrongly reports every one of that namespace's children as a missing required input:

class Window(TypedDict):
    """An energy window: both bounds, or neither."""

    lower: float
    upper: float


@task
def count_states(energies: list, window: Window | None = None) -> int:
    """Count the energies, optionally restricted to a window."""
    if window is None:
        return len(energies)
    return len([e for e in energies if window['lower'] <= e <= window['upper']])


wg = WorkGraph('example')
wg.add_task(count_states, name='count_states', energies=[-1.0, 0.5, 2.0])
wg.run()

window has a None default and the function handles its absence, but the graph will not run:

ValueError: Missing required inputs:
  • count_states.window.lower
  • count_states.window.upper

The namespace socket itself is correctly marked required = False; only its children are required. find_missing_inputs recurses into the children without consulting the parent, so their requiredness is read as absolute rather than conditional on the namespace being supplied at all.

Changes

• An optional namespace nobody filled in is not missing anything: in this instance skip the recursion.
• Add WorkGraph.is_socket_provided, which performs this "anything in the subtree" test (doing so recursively to catch namespaces whose child is linked from an upstream task).
• A namespace that is partially supplied still reports its missing children, and a required namespace is unaffected.

Testing

tests/test_validation.py covers four cases:

• An optional namespace left entirely empty reports nothing. This is the desired fix, and fails without the change.
• An optional namespace with one of two children supplied still reports the other.
• An optional namespace with one child linked from an upstream task output likewise still reports the unlinked child.
• A required namespace left empty still reports both children, i.e. existing behaviour is untouched.

Reverting the source change leaves the last three passing but fails the first.