Eric Blake <ebl...@redhat.com> writes:
> On 02/20/2014 07:43 AM, Markus Armbruster wrote:
>> Wenchao Xia <xiaw...@linux.vnet.ibm.com> writes:
>>
>>> It will check whether base is set, whether discriminator is found
>>> in base, whether the values specified are written correctly, and
>>> whether all enum values are covered, when discriminator is a
>
>>
>> And every member of the discriminator enum type must also occur as key
>> of the union's member 'data'. Why?
>>
>> Consider:
>>
>> { 'enum': 'FooEnum', 'data': [ 'plain', 'bells', 'whistles' ] }
>>
>> { 'type': 'CommonFooOptions',
>> 'data': { 'type: 'FooType', 'readonly': 'bool' } }
>> { 'union': 'FooOptions',
>> 'base': 'CommonFooOptions',
>> 'discriminator': 'type',
>> 'data': { 'bells': 'BellsOptions',
>> 'whistles': 'WhistlesOptions' } }
>>
>> Type 'plain' doesn't have options beyond CommonFooOptions.
>
> I'd still rather make it explicit that we KNOW that this branch of the
> union has no additional options:
>
> { 'union': 'FooOptions',
> 'base': 'CommonFooOptions',
> 'discriminator': 'type',
> 'data': { 'plain': {},
> 'bells': 'BellsOptions',
> 'whistles': 'WhistlesOptions' } }
>
> to show that we explicitly thought about all the cases. We don't
> currently have any such unions with an empty branch, but it would be
> worth documenting in the qapi text and explicitly testing that it works
> if we intend to support this.
Fair point. However, it requires 'plain': {} to work, and it doesn't in
my testing. When I add "'c': {}" to qapi-schema-test.json's
UserDefFlatUnion like this:
{ 'union': 'UserDefFlatUnion',
'base': 'UserDefOne',
'discriminator': 'string',
'data': { 'a' : 'UserDefA', 'b' : 'UserDefB', 'c': {} } }
the generator gives me
struct UserDefFlatUnion
{
UserDefFlatUnionKind kind;
union {
void *data;
UserDefA * a;
UserDefB * b;
---> void c;
};
bool has_enum1;
EnumOne enum1;
};
which doesn't compile. This is only the first compile error, there are
more.
We should extend the generator to permit {} before we insist on unions
covering all discriminator values explicitly. Because if we don't,
people will be compelled to add dummy fields.
