loads() silently drops falsy kwarg values (device_qubits=0, device_cycle_time=0.0, ...) #356

Description

loads() stores six of its documented kwargs with a walrus truthiness test rather than a presence test:

if dev_qbts := kwargs.get("device_qubits"):
    module._device_qubits = dev_qbts

So any falsy value is silently treated as "not passed" — no error, no warning, the caller's argument is discarded. entrypoint.py:103-116.

The same function already uses the correct pattern for its two bool kwargs:

if "frame_in_def_cal" in kwargs:
    module._frame_in_def_cal = kwargs["frame_in_def_cal"]

Reproduction

from pyqasm import loads

src = 'OPENQASM 3.0;\ninclude "stdgates.inc";\nqubit[2] q;\nh q[0];\n'

loads(src, device_qubits=0)._device_qubits                 # None  <- expected 0
loads(src, device_cycle_time=0.0)._device_cycle_time       # None  <- expected 0.0
loads(src, compiler_angle_type_size=0)._compiler_angle_type_size  # None
loads(src, frame_limit_per_port=0)._frame_limit_per_port   # None

loads(src, frame_in_def_cal=False)._frame_in_def_cal       # False <- correctly honoured

Scope

Pre-existing on main; unrelated to any open PR.

extern_functions={} is affected by the same test but is harmless in practice — the attribute already defaults to {}, so the dropped value is indistinguishable from the default. The four Optional[...] = None attributes above are the ones where a caller's 0 becomes None.

Two adjacent gaps in the same block, worth deciding on together:

• No value validation. Negative values are truthy, so they are stored and surface later as a confusing message rather than being rejected at the call site:

  m = loads(src, device_qubits=-5)
  m.validate()   # ValidationError: Total qubits '2' exceed device qubits '-5'.

• Unknown kwargs are silently ignored. loads(src, devise_qubits=5) raises nothing and produces a module with _device_qubits = None. A typo in a documented kwarg is invisible until the resulting behaviour is wrong.

Suggested fix

Use presence tests consistently for all of them:

if "device_qubits" in kwargs:
    module._device_qubits = kwargs["device_qubits"]

Optionally reject non-positive device_qubits / device_cycle_time / frame_limit_per_port at load time, and raise on unrecognised kwarg names, so mistakes fail where they are made.

Found while verifying #349, which documents device_qubits as a loads() kwarg.