Re: [Qemu-devel] [PATCH RFC v2 27/47] qapi-visit: Convert to QAPISchemaVisitor, fixing bugs

[Eric Blake]

On 07/29/2015 02:00 AM, Markus Armbruster wrote:
>>>> We don't have any code that demonstrates this, but probably should.  I
>>>> ran into it while working up my POC of what it would take to unbox
>>>> inherited structs 
>>>> (http://thread.gmane.org/gmane.comp.emulators.qemu/353204)
>>>
>>> Is this broken in master, or do my patches break it?
>>>
>>> Got a reproducer?
>>
>> Turns out I'm mistaken; we got lucky.  The call to
>> generate_visit_struct_fields() creates a function for 'name' (aka the
>> union name), and not for 'base' (aka the class name that owns the
>> fields).  So even if we have Base as a common struct between Child and
>> Union, the code emitted for Child generates visit_Base_fields(), while
>> the code emitted for Union generates visit_Union_fields().
>>
>> So there is no reproducer, but _only_ as long as we reject unions as a
>> base class for any other object.  And there is redundancy: we could
>> reuse visit_Base_fields() for the sake of the union, then avoid
>> (re-)visiting the discriminator, and we would no longer need to emit
>> visit_Union_fields().  But I can do that as part of the followup
>> cleanups; since I don't see anything broken with your patch, we don't
>> have to worry about it during this series.
> 
> Good.  Thank you!

And here's a followup patch that cleans it up:
http://thread.gmane.org/gmane.comp.emulators.qemu/353204/focus=353728

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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