Re: [Qemu-devel] [PATCH RFC v3 02/32] qapi: New QAPISchema intermediate reperesentation

[Eric Blake <eblake@redhat.com>]

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On 08/05/2015 12:23 AM, Markus Armbruster wrote:
> Eric Blake <eblake@redhat.com> writes:
> 
>> On 08/04/2015 09:57 AM, Markus Armbruster wrote:
>>> The QAPI code generators work with a syntax tree (nested dictionaries)
>>> plus a few symbol tables (also dictionaries) on the side.
>>>

>>> +class QAPISchemaArrayType(QAPISchemaType):
>>> +    def __init__(self, name, info, element_type):
>>> +        QAPISchemaType.__init__(self, name, info)
>>> +        assert isinstance(element_type, str)
>>> +        self.element_type_name = element_type
>>> +        self.element_type = None
>>> +    def check(self, schema):
>>> +        self.element_type = schema.lookup_type(self.element_type_name)
>>> +        assert self.element_type
>>
>> Is it worth adding:
>>
>> assert not isinstance(self.element_type, QAPISchemaArrayType)
>>
>> since we don't allow 2D arrays?
> 
> If the generators actually rely on it, yes.

Hmm. What happens if you do
 { 'command': 'Foo', 'returns': [ 'intList' ] }

> 
> If it's just an arbitrary schema language restriction, probably no.

That's a tough judgment call. We don't currently allow [ [ 'int' ] ],
and the [ 'intList' ] hack is gross. On the other hand, I'm having a
tough time coming up with technical reasons why we can't do it (arrays
as a parameter or return type should work, and 2D arrays just add
another layer of '*' to the C code).

>>> +    def _make_array_type(self, element_type):
>>> +        name = element_type + 'List'
>>> +        if not self.lookup_type(name):
>>> +            self._def_entity(QAPISchemaArrayType(name, None, element_type))
>>> +        return name
>>
>> Hmm - we probably have collisions if a user tries to explicitly name a
>> 'struct' or other type with a 'List' suffix.  Not made worse by this
>> patch and not an actual problem with any of our existing .json files, so
>> we can save it for another day.
> 
> qapi-code-gen.txt reserves the 'Kind' suffix.
> 
> We should either adopt a sane, non-colliding scheme for generated names,
> or prevent collisions by rejecting reserved names with a sane error
> message (documenting them is then optional), or document reserved names.
> The latter two require us to figure out what names we reserve.  But as
> you say, it's a task for another day.

And that cleanup can worry about [ 'intList' ].

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


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