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From: Markus Armbruster <armbru@redhat.com>
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Date: Tue, 08 Mar 2016 19:10:59 +0100
In-Reply-To: <56DEFAE3.7040704@redhat.com> (Eric Blake's message of "Tue, 8
	Mar 2016 09:16:35 -0700")
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Subject: Re: [Qemu-devel] [PATCH v4 07/10] qapi: Don't special-case simple
	union wrappers
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To: Eric Blake <eblake@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Fam Zheng <famz@redhat.com>, Eduardo Habkost <ehabkost@redhat.com>, "open list:Block layer core" <qemu-block@nongnu.org>, "Michael S. Tsirkin" <mst@redhat.com>, Jan Kiszka <jan.kiszka@siemens.com>, Jason Wang <jasowang@redhat.com>, Michael Roth <mdroth@linux.vnet.ibm.com>, Vincenzo Maffione <v.maffione@gmail.com>, qemu-devel@nongnu.org, Gerd Hoffmann <kraxel@redhat.com>, Igor Mammedov <imammedo@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Giuseppe Lettieri <g.lettieri@iet.unipi.it>, Luiz Capitulino <lcapitulino@redhat.com>, Luigi Rizzo <rizzo@iet.unipi.it>, Samuel Thibault <samuel.thibault@ens-lyon.org>

Eric Blake <eblake@redhat.com> writes:

> On 03/08/2016 08:59 AM, Markus Armbruster wrote:
>> Eric Blake <eblake@redhat.com> writes:
>> 
>>> Simple unions were carrying a special case that hid their 'data'
>>> QMP member from the resulting C struct, via the hack method
>>> QAPISchemaObjectTypeVariant.simple_union_type().  But by using
>>> the work we started by unboxing flat union and alternate
>>> branches, coupled with the ability to visit the members of an
>>> implicit type, we can now expose the simple union's implicit
>>> type in qapi-types.h:
>>>
>
>>> +++ b/scripts/qapi.py
>>> @@ -1006,7 +1006,6 @@ class QAPISchemaObjectType(QAPISchemaType):
>>>          return c_name(self.name) + pointer_suffix
>>>
>>>      def c_unboxed_type(self):
>>> -        assert not self.is_implicit()
>> 
>> Doesn't this belong into PATCH 04?
>> 
>>>          return c_name(self.name)
>
> Maybe. Patch 3 kept the assertion out of straight code refactoring, and
> patch 4 didn't use c_unboxed_type(), so this was the first place where I
> had to weaken the assertion.  But moving it into patch 4 doesn't seem
> like it would hurt, as it is still semantically related to the fact that
> we are planning on allowing an unboxed implicit type.

PATCH 04 drops the assertion from c_name().  Let's keep the two
consistent.

>>> -        visit_type_%(c_type)s_members(v, &obj->u.%(c_name)s, &err);
>>> -''',
>>> -                             c_type=var.type.c_name(),
>>> -                             c_name=c_name(var.name))
>>> -            ret += mcgen('''
>>> -        break;
>>> -''')
>>> +                                           variants.tag_member.type.prefix),
>>> +                         c_type=var.type.c_name(), c_name=c_name(var.name))
>>>
>>>          ret += mcgen('''
>>>      default:
>> 
>> This stupid special case has given us enough trouble, good to see it
>> gone!
>
> Yeah, it was a nice feeling to get to this point!