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Re: [Qemu-devel] [PATCH v4 01/10] qapi: Assert in places where variants
From: |
Markus Armbruster |
Subject: |
Re: [Qemu-devel] [PATCH v4 01/10] qapi: Assert in places where variants are not handled |
Date: |
Tue, 08 Mar 2016 18:46:35 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) |
Eric Blake <address@hidden> writes:
> On 03/08/2016 03:12 AM, Markus Armbruster wrote:
>> Eric Blake <address@hidden> writes:
>>
>>> We are getting closer to the point where we could use one union
>>> as the base or variant type within another union type (as long
>>> as there are no collisions between any possible combination of
>>> member names allowed across all discriminator choices). But
>>> until we get to that point, it is worth asserting that variants
>>> are not present in places where we are not prepared to handle
>>> them: base types must still be plain structs, and anywhere we
>>> explode a struct into a parameter list (events and command
>>> marshalling), we don't support variants in that explosion.
>>>
>>> Signed-off-by: Eric Blake <address@hidden>
>>>
>
>>> +++ b/scripts/qapi.py
>>> @@ -960,6 +960,7 @@ class QAPISchemaObjectType(QAPISchemaType):
>>> assert isinstance(self.base, QAPISchemaObjectType)
>>> self.base.check(schema)
>>> self.base.check_clash(schema, self.info, seen)
>>> + assert not self.base.variants
>>
>> I'd move this two lines up, so it's next to the isinstance.
>>
>> Assertions in .check() are place-holders for semantic checks that
>> haven't been moved from the old semantic analysis to the classes.
>> Whenever we add one, we should double-check the old semantic analysis
>> catches whatever we assert. For object types, that's check_struct() and
>> check_union(). Both check_type() the base with allow_metas=['struct']),
>> so we're good.
>>
>> Inconsistency: you add the check for base, but not for variants.
>>
>> On closer look, adding it for either is actually redundant, because
>> se.f.base.check_clash() already asserts it, with a nice "not
>> implemented" comment.
>>
>> If we think asserting twice is useful for base, then it's useful for
>> variants, too. But I think asserting once suffices.
>
> So basically, we can drop this hunk, right?
Yes.
[Qemu-devel] [PATCH v4 03/10] qapi: Make c_type() more OO-like, Eric Blake, 2016/03/05
[Qemu-devel] [PATCH v4 02/10] qapi: Fix command with named empty argument type, Eric Blake, 2016/03/05
[Qemu-devel] [PATCH v4 08/10] qapi: Allow anonymous base for flat union, Eric Blake, 2016/03/05
[Qemu-devel] [PATCH v4 10/10] qapi: Populate info['name'] for each entity, Eric Blake, 2016/03/05