Re: [Qemu-devel] [PATCH v11 03/15] qapi: Forbid 'any' inside an alternate

[Eric Blake <eblake@redhat.com>]

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On 02/18/2016 05:05 AM, Markus Armbruster wrote:
> Eric Blake <eblake@redhat.com> writes:
> 
>> The whole point of an alternate is to allow some type-safety while
>> still accepting more than one JSON type.  Meanwhile, the 'any'
>> type exists to bypass type-safety altogether.  The two are
>> incompatible: you can't accept every type, and still tell which
>> branch of the alternate to use for the parse; fix this to give a
>> sane error instead of a Python stack trace.
>>
>> Signed-off-by: Eric Blake <eblake@redhat.com>
>>

> 
> Interestingly, find_alternate_member_qtype(T) can return None in two
> ways: when builtin_types[T] is None (only for T == 'any'), and when T is
> neither built-in, struct, enum or union (it must be alternate then).
> 
> This leads to the question whether this patch catches exactly 'any', as
> the commit message claims, or alternate as well.
> 

>> 
>> @@ -629,7 +629,10 @@ def check_alternate(expr, expr_info):
>>                     value,
>>                     allow_metas=['built-in', 'union', 'struct', 'enum'])
>>          qtype = find_alternate_member_qtype(value)
> 

> 
> Could use a test for alternate member of alternate type.

One step ahead of you: commit 3d0c4829 added the test
alternate-nested.json, and commits 44bd1276 and dd883c6f fixed the
parser to reject it (first by a hard-coded check, then via allow_metas[]
excluding alternates).  'any' is the only value that could sneak
through, because it is a subset of 'built-in' which allow_metas[]
whitelisted.

If you want to squash any of this information into the commit message,
though, I don't mind.

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


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