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From: Markus Armbruster <armbru@redhat.com>
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Date: Fri, 31 Jul 2015 11:46:38 +0200
In-Reply-To: <87lhdzju4i.fsf@blackfin.pond.sub.org> (Markus Armbruster's
	message of "Wed, 29 Jul 2015 09:33:17 +0200")
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Subject: Re: [Qemu-devel] [PATCH RFC v2 07/47] qapi: Generate a nicer struct
	for flat unions
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To: Eric Blake <eblake@redhat.com>
Cc: kwolf@redhat.com, berto@igalia.com, qemu-devel@nongnu.org, mdroth@linux.vnet.ibm.com

Markus Armbruster <armbru@redhat.com> writes:

> Eric Blake <eblake@redhat.com> writes:
>
>> On 07/01/2015 02:21 PM, Markus Armbruster wrote:
>>> The struct generated for a flat union is weird: the members of its
>>> base are at the end, except for the union tag, which is renamed to
>>> 'kind' and put at the beginning.
>>
>> The renaming to 'kind' was a bug waiting to happen.  Consider this
>> example, which is broken before your series:
>>
>> diff --git i/tests/qapi-schema/qapi-schema-test.json
>> w/tests/qapi-schema/qapi-schema-test.json
>> index c7eaa86..12c09e3 100644
>> --- i/tests/qapi-schema/qapi-schema-test.json
>> +++ w/tests/qapi-schema/qapi-schema-test.json
>> @@ -37,7 +37,7 @@
>>    'data': { 'string1': 'str', 'string2': 'str' } }
>>
>>  { 'struct': 'UserDefUnionBase',
>> -  'data': { 'string': 'str', 'enum1': 'EnumOne' } }
>> +  'data': { 'kind': 'str', 'enum1': 'EnumOne' } }
>>
>>  { 'union': 'UserDefFlatUnion',
>>    'base': 'UserDefUnionBase',
>>
>>
>> leading to this compilation error during 'make check-unit':
>>
>> In file included from tests/test-qmp-output-visitor.c:17:0:
>> tests/test-qapi-types.h:617:11: error: duplicate member =E2=80=98kind=E2=
=80=99
>>      char *kind;
>>            ^
>> tests/test-qapi-types.h:631:11: error: duplicate member =E2=80=98kind=E2=
=80=99
>>      char *kind;
>>            ^
>>
>> Therefore, it might be worth mentioning that avoiding the rename to
>> 'kind' is a bug fix, not just a nicer struct :)
>
> Cool!  I'll work (a variation of) this test case into my series.

I split the bug fix off this patch.  I put the test in the commit
message, because I feel it has little value as regression test going
forward.