Tools to disable op validation

[95-martin-orion]

Fixes #5517.

Does what it says on the tin: turns off op validation in the provided context. The try/except block in the manager ensures that validation is always re-enabled, regardless of what terrible things happen in the context.

[maffoo]

Consider using a ContextVar rather than modifying global state.

[maffoo]

Only need the finally clause here. It'll run on failure too.

[maffoo]

We might consider using contextvars instead:

# raw_types.py
validate_qids: contextvars.ContextVar[bool] = contextvars.ContextVar('validate_qids', default=True)

def _validate_qid_shape(...) -> None:
    if validate_qids.get():
        return
    ...

# here
def disable_op_validation(...):
    ...
    token = raw_types.validate_qids.set(False)
    try:
        yield
    finally:
        raw_types.validate_qids.reset(token)

This would be more scoped than modifying global state, which could otherwise cause hard-to-debug issues with threads or asynchrony.

[95-martin-orion]

Done. My only misgiving with this is that it exposes the hack in raw_types.py, which could lead to users applying it in ill-advised ways. Left a comment to mitigate this somewhat.

[maffoo]

After thinking about it, I think I agree with you that it's better to keep the hack itself contained and not modify raw_types.py. If this turns out to be useful and we can't otherwise optimize the qid validation then we could migrate it into raw_types in the future. So feel free to ignore my suggestions and revert to your original version.

[maffoo]

Can revert the contextvars suggestion, then LGTM.

[95-martin-orion]

Ended up needing to twiddle the tests to get coverage happy, but changes were fairly minor.

[CirqBot]

Automerge cancelled: A status check is failing.