Re: [Qemu-devel] QMP accepts double dict keys

[Daniel P . Berrangé]

On Mon, Dec 03, 2018 at 01:57:13PM -0600, Eric Blake wrote:
> On 12/3/18 1:48 PM, Markus Armbruster wrote:
> > Eric Blake <address@hidden> writes:
> > 
> > > On 12/3/18 10:30 AM, Max Reitz wrote:
> > > > Hi,
> > > > 
> > > > QMP accepts double keys in dicts without complaining.  The value it is
> > > > using is apparently the last one specified:
> > > 
> > > JSON says it is undefined what happens when a client passes double
> > > keys. We are probably best off if we teach our parser to be strict and
> > > reject doubled keys in QMP as invalid.
> > 
> > Not bug-compatible.  Do we care?
> 
> I don't think so. Such a client was already invoking undefined behavior.
> Relying on first- or last-past-the-post to win is not portable, since JSON
> parsers are allowed to use hash tables with non-deterministic lookups. I
> think erroring out is nicer than silently accepting one thing, especially if
> that might have been different than what the client (incorrectly) expected.
> I'm not even sure that we would want a deprecation period.

Erroring out immediately, without any deprecation period sounds fine
to me, as this is simply a bug fix.

IMHO the ABI/API compatibility stability only applies to things that
are intended behaviour / correct usage.

Regards,
Daniel
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