Re: [netmod] augment and if-feature

Hi,

On 15/03/2017 07:28, Martin Bjorklund wrote:
> Phil Shafer <phil@juniper.net> wrote:
>> Martin Bjorklund writes:
>>> Phil Shafer <phil@juniper.net> 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.

>
>> 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.

Rob

>>
>> Thanks,
>>   Phil
>>
>
> /martin
>
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