Re: [Qemu-devel] [PATCH 2/2] qapi: deprecate implicit filters

[John Snow <jsnow@redhat.com>]

On 8/23/19 5:22 AM, Vladimir Sementsov-Ogievskiy wrote:
> 14.08.2019 13:07, Vladimir Sementsov-Ogievskiy wrote:
>> To get rid of implicit filters related workarounds in future let's
>> deprecate them now.
> 
> Interesting, could we deprecate implicit filter without deprecation of unnecessity of
> parameter? As actually, it's good when this parameter is not necessary, in most cases
> user is not interested in node-name.
> 

https://en.wiktionary.org/wiki/unnecessity -- I am surprised to learn
that this a real word in the language I speak. :)

I assume you're referring to making the optional argument mandatory.

> Obviously we can do the following:
> 
> 1. In 4.2 we deprecate unnecessity, which implies deprecation of implicit filters
> 2. After some releases in 4.x we can drop deprecated functionality, so we drop it together with
> implicit filters. And, in same release 4.x we return it back (as it's compatible change :)
> but without implicit filters (so, if filter-node-name not specified, we just create
> explicit filter with autogenerated node-name)
> 
> So, effectively we just drop "deprecation mark" together with implicit filters, which is nice
> but actually confusing.
> 
> Instead, we may do
> 1. In 4.2 deprecate
> 2. In 4.x drop optionality together with implicit filters
> 3. In 4.y (y > x of course) return optionality back
> 

Ah, I see what you're digging at here now...

> It's a bit safer, but for users who miss releases [4.x, 4.y) it's no difference..
> 
> Or we just write in spec, that implicit filters are deprecated? But we have nothing about implicit
> filters in spec. More over, we directly write that we have filter, and if parameter is omitted
> it's node-name is autogenerated. So actually, the fact the filter is hidden when filter-node-name is
> unspecified is _undocumented_.
> 
> So, finally, it looks like nothing to deprecated in specification, we can just drop implicit filters :)
> 
> What do you think?
> 

What exactly _IS_ an implicit filter? How does it differ today from an
explicit filter? I assumed the only difference was if it was named or
not; but I think I must be mistaken now if you're proposing leaving the
interface alone entirely.

Are they instantiated differently?

--js