Re: [Qemu-devel] [PATCH v11 13/28] qapi: Hoist tag collision check to Variants.check()

[Eric Blake]

On 11/11/2015 06:56 AM, Markus Armbruster wrote:
> Eric Blake <address@hidden> writes:
> 
>> Checking that a given QAPISchemaObjectTypeVariant.name is a
>> member of the corresponding QAPISchemaEnumType of the owning
>> QAPISchemaObjectTypeVariants.tag_member ensures that there are
>> no collisions in the generated C union for those tag values
>> (since the enum itself should have no collisions).
>>
>> However, this check was the only thing that Variant.check() was
>> doing beyond the work of the superclass ObjectTypeMember.check(),
> 
> Since PATCH 05, actually.  Suggest to mention that.

I debated about munging patch 5 or 6 to actually make this change there;
but decided that separate is just fine.  But yes, mentioning the earlier
commit title will help.

>> @@ -1075,10 +1076,6 @@ class 
>> QAPISchemaObjectTypeVariant(QAPISchemaObjectTypeMember):
>>      def __init__(self, name, typ):
>>          QAPISchemaObjectTypeMember.__init__(self, name, typ, False)
>>
>> -    def check(self, schema, tag_type):
>> -        QAPISchemaObjectTypeMember.check(self, schema)
>> -        assert self.name in tag_type.values
>> -
>>      # This function exists to support ugly simple union special cases
>>      # TODO get rid of them, and drop the function
>>      def simple_union_type(self):
> 
> QAPISchemaObjectTypeVariant is now an almost trivial variation of
> QAPISchemaObjectTypeMember.  Differences:
> 
> * __init__() has no parameter optional
> 
> * Method simple_union_type(), which exists only to support pointless
>   differences in code generation for simple unions, all marked TODO.
> 
> There's hope we can get rid of the class after the TODOs are resolved.

Nope. Because in 15/28 I add back in a non-trivial difference of "role =
'branch'" compared to the superclass "role = 'member'", which affects
the quality of error messages using .describe().

That, and I still have no idea how to get rid of the TODO (we know how
to convert simple unions to flat unions, but the conversion is an
either-or choice: either we keep the C layout the same but change {} in
the JSON representation, or we keep QMP the same but affect the C layout
- so fixing the TODO has to resolve that discrepancy, and may end up
touching lots of code).

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

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