Re: [netmod] augment and if-feature

[Robert Wilton <[e-mail]>]

On 15/03/2017 10:20, Martin Bjorklund wrote:
> Robert Wilton <[e-mail]> wrote:
>> Hi,
>>
>> On 15/03/2017 07:28, Martin Bjorklund wrote:
>>> Phil Shafer <[e-mail]> wrote:
>>>> Martin Bjorklund writes:
>>>>> Phil Shafer <[e-mail]> wrote:
>>>>>> Martin Bjorklund writes:
>>>>>>>> What are your thoughts on this? Surely, an augment should not have to
>>>>>>>> contain if-feature statements of all parents of the augmented node.
>>>>>>> The spec says:
>>>>>>>
>>>>>>>     When a server implements a module containing an "augment" statement,
>>>>>>>     that implies that the server's implementation of the augmented module
>>>>>>>     contains the additional nodes.
>>>>>>>
>>>>>>> Compare with a simple augment of a node w/o an if-feature.  In this
>>>>>>> case, if the server implements the augmenting module, it MUST also
>>>>>>> implement the augmented module.
>>>>>> It implements the module, but it doesn't implement the nodes
>>>>>> since it doesn't express the feature.  IMHO this is a tool
>>>>>> bug and/or an errata,since otherwise one has to carry features
>>>>>> forward, repeating the if-feature using the original modules
>>>>>> prefix:feature-name on every augment of feature-based nodes.
>>>>> Well, I agree that it would have been better to state that if a server
>>>>> doesn't implement the augment target, then it doesn't implement the
>>>>> augment either.  But the text is pretty clear; this is not how it
>>>>> works.  This is not appropriate to "fix" in an errata.
>>>> I'm missing the part of the text that's clear.  The above quoted
>>>> section certainly doesn't say this.  That text is saying "if you
>>>> implement a module that augments a set of nodes, then the server's
>>>> schema for that original set of nodes now includes the new set of
>>>> nodes".  It's referring to schema nodes.
>>> It explicitly says that server's *implementation* of the augmented
>>> module contains the additional nodes.
>> Section "5.6.5.  Implementing a Module", doesn't mention features at
>> all.
>> Section "5.6.2.  Optional Features" doesn't mention implementation at
>> all.  It only writes about portions of a model that are conditional,
>> supported, or valid.
>> Section "7.20.1.  The "feature" Statement" also doesn't mention
>> implementation, it only writes about portions of the model being
>> conditional.
>>
>> So, I find the text that you are quoting as ambiguous in respect to
>> its applicability to features.
>>
>>
>>
>>> If you don't advertise a certain module, I don't think you can claim
>>> that your implementation contains that module.
>> I agree with this.
>>
>>> And similarly, if you don't advertise a feature, I don't think you can
>>> claim that your implementation implements nodes that are conditional
>>> on that feature.
>> I'm not convinced that the RFC text supports this view.  The nodes
>> could be implemented but conditionally not supported.
> The same can be said about a whole module; it could be implemented but
> temporarily disabled.
>
>>>> And if those schema nodes are conditional based on if-feature, then
>>>> those nodes are still in the schema, but are not supported by a
>>>> server unless the if-feature condition evaluates to true.
>>>>
>>>> I don't see a conflict,
>>>> it's just a case that we didn't think about
>>>> or write about.
>>> This I agree with.
>>>
>>>> It's a case that's not clearly handled in the spec,
>>>> for which reasonable implementations can disagree.  That's a bug
>>>> in the spec and it that can be clarified via errata.
>> I also think that this needs to be clarified one way or the other.
>>
>> I would also prefer it to be allowed to augment a node that is
>> conditional on an if-feature without having to restate the if-feature
>> condition, in exactly the same way that it is allowed to augment a
>> node with a when statement without having to restate the when
>> statement in the augmentation.
> Just to be clear - I prefer this as well.  I also think the same thing
> applies to normal augment w/o features; if you implement module A that
> has an augment of B, and you don't implement B, you should
> still be able to state that you implement A.
>
> But I don't think it can be done in an errata.
Does this just leave the behaviour as undefined then? I.e. it is up to 
the implementation to decide whether they error the augmentation.

Rob

>
>
> /martin
> .
>