On 03/02/2016 12:04 PM, Markus Armbruster wrote: > Eric Blake <ebl...@redhat.com> writes: > >> And use it in qapi-types and qapi-event. Down the road, we may >> want to lift our artificial restriction of no variants at the >> top level of an event, at which point, inlining our check for >> whether members is empty will no longer be sufficient, but >> adding a check for variants adds verbosity; in the meantime, >> add some asserts in places where we don't handle variants. > > Perhaps I'm just running out of steam for today, but I've read this > twice, and still don't get why adding these assertions goes in the same > patch as adding the helper, or what it has to do with events.
And yet it was the review on the earlier posting that caused me to add asserts; maybe re-reading that thread will help refresh memory, and spur an idea for how to better express it in the commit message: https://lists.gnu.org/archive/html/qemu-devel/2016-01/msg04726.html > >> More immediately, the new .is_empty() helper will help fix a bug >> in qapi-visit in the next patch, where the generator did not >> handle an explicit empty type in the same was as a missing type. > > same way [Ever wonder if I intentionally stick in a typo, just to see who will notice? Or maybe it really was a slip of the finger...] >> +++ b/scripts/qapi-event.py >> @@ -39,7 +39,7 @@ def gen_event_send(name, arg_type): >> ''', >> proto=gen_event_send_proto(name, arg_type)) >> >> - if arg_type and arg_type.members: >> + if arg_type and not arg_type.is_empty(): >> ret += mcgen(''' >> QmpOutputVisitor *qov; >> Visitor *v; > > Oh, you don't just add a helper, you actually *change* the condition! > Perhaps the commit message would be easier to understand if it explained > that first. The old condition: arg_type and arg_type.members New condition: arg_type and (arg_type.members or arg_type.variants) But we know there are no variants, since unions cannot (yet) be passed as event 'data', so the condition is the same effect now, and future-proofing for a future patch when I do allow unions in events. >> +++ b/scripts/qapi-types.py >> @@ -90,7 +90,7 @@ struct %(c_name)s { >> # potential issues with attempting to malloc space for zero-length >> # structs in C, and also incompatibility with C++ (where an empty >> # struct is size 1). >> - if not (base and base.members) and not members and not variants: >> + if (not base or base.is_empty()) and not members and not variants: >> ret += mcgen(''' >> char qapi_dummy_for_empty_struct; >> ''') > > I figure the case for the helper based on this patch alone is making the > code a bit more future-proof. Suggest you try to explain that in your > commit message, including against what future change exactly you're > proofing the code. And here, bases cannot (yet) have variants, but that's also on my plate of things I'd like to support in the future. > > Haven't reviewed for completeness. > -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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