Re: [yang-doctors] Fwd: Re: Issue with [e-mail] and yangdump-pro

[Ladislav Lhotka <[e-mail]>]

On Sat, 2017-12-23 at 13:01 +0100, Martin Bjorklund wrote:
> Andy Bierman <[e-mail]> wrote:
> > On Sat, Dec 23, 2017 at 2:21 AM, Martin Bjorklund <[e-mail]> wrote:
> > 
> > > Hi,
> > > 
> > > See section 9.10.3 in RFC 7950:
> > > 
> > >    The string value of a node of type "identityref" in a "must" or
> > >    "when" XPath expression is the referred identity's qualified name
> > >    with the prefix present.
> > > 
> > > and re. the prefix:
> > > 
> > >    If the referred identity is defined in an
> > >    imported module, the prefix in the string value is the prefix defined
> > >    in the corresponding "import" statement.  Otherwise, the prefix in
> > >    the string value is the prefix for the current module.
> > > 
> > > 
> > > I most cases you should consider using derived-from-or-self instead of
> > > equality test for identiyrefs.
> > > 
> > > 
> > 
> > So what is "the current module"?
> > What is the resolution of 'X'? Is it foo:X or bar:X?
> 
> foo:X

No, the resolution of 'X' is 'X' because it is an XPath 1.0 string and XPath
knows nothing about YANG identities. Because of the rule of sec. 9.10.3, the
equality expression is always false.

That's why we introduced the new XPath functions derived-from() and derived-
from-or-self() in YANG 1.1.

Lada 

> 
> 
> /martin
> 
> 
> > 
> > 
> > 
> > > 
> > > /martin
> > > 
> > > 
> > 
> > Andy
> > 
> > 
> > > 
> > > 
> > > 
> > > Andy Bierman <[e-mail]> wrote:
> > > > On Fri, Dec 15, 2017 at 4:38 AM, Radek Krejčí <[e-mail]> wrote:
> > > > 
> > > > > Hi,
> > > > > I'm adding Michal Vasko to cc, he knows better how these things are
> > > > > checked in libyang.
> > > > > 
> > > > > It seems to me that Andy refers the text which does not apply here.
> > > > > The
> > > > > identity name was used as part of XPath expresion (when-stmt), so the
> > > > > definition of the context nodes for the when-stmt (RFC 7950, sec
> > > 
> > > 7.21.5)
> > > > > and XPath context rules should apply here. Not the rules for the
> > > > > identityref's base statement. In this case, the when-stmt is in
> > > 
> > > augment so
> > > > > the context node (which we also understand as the current node in this
> > > > > case) is the augment's target node. And according to XPath context
> > > 
> > > rules
> > > > > (RFC 7950, sec 6.4.1):
> > > > > 
> > > > >  o  Names without a namespace prefix belong to the same namespace as
> > > 
> > > the
> > > > > identifier of the current node.
> > > > > 
> > > > 
> > > > 
> > > > I cc:ed YANG doctors to get more opinions...
> > > > 
> > > > The current node is the augment-stmt.
> > > > Note that it does not say context node, which is the target of the
> > > 
> > > augment.
> > > > I think prefixes (and default prefix) are resolved in the module
> > > 
> > > containing
> > > > the statement.
> > > > 
> > > > 
> > > > module foo {
> > > > 
> > > >    import bar { prefix b; }
> > > >    identity X;
> > > > 
> > > >    augment b:/some-node {
> > > >       leaf test {
> > > >          type string;
> > > >          when "/b:some-node/b:other-node = 'X'";
> > > >       }
> > > >    }
> > > > }
> > > > 
> > > > module bar {
> > > > 
> > > >    identity W;
> > > >    identity X { base W; }
> > > >    container some-node {
> > > >        leaf other-node {
> > > >          type identityref { base W; }
> > > >        }
> > > >    }
> > > > }
> > > > 
> > > > Q) Does other-node = 'X' resolve to foo:X or bar:X?  IMO: foo:X
> > > > 
> > > > 
> > > > 
> > > > Andy
> > > > 
> > > > 
> > > > 
> > > > > In this particular case, the augment node with the when-stmt augments
> > > 
> > > the
> > > > > same module which defines napt44, so they are in the correct namespace
> > > 
> > > and
> > > > > the identity name can be used without the prefix. So it should be
> > > > > fine,
> > > > > while I believe that using prefix in the cases of identities is always
> > > > > better approach. From the first sight (it may be challenging for human
> > > 
> > > to
> > > > > correctly resolve the context/current node in some cases), I would
> > > > > also
> > > > > expect prefix.
> > > > > 
> > > > > I propose to keep the change in the draft (added nat prefix), since it
> > > > > improves readability of the expression. But I don't think that it is
> > > > > an
> > > > > error to ommit the prefix.
> > > > > 
> > > > > Regards,
> > > > > Radek
> > > > > 
> > > > > 
> > > > > Dne 19.11.2017 v 20:42 Benoit Claise napsal(a):
> > > > > > Hi Radek,
> > > > > > 
> > > > > > Here is a bug report for you.
> > > > > > 
> > > > > > Regards, Benoit
> > > > > > 
> > > > > > 
> > > > > > -------- Forwarded Message --------
> > > > > > Subject:      Re: Issue with [e-mail] and
> > > > > 
> > > > > yangdump-pro
> > > > > > Date:         Sat, 18 Nov 2017 13:22:58 -0800
> > > > > > From:         Andy Bierman <[e-mail]>
> > > > > > To:   Benoit Claise <[e-mail]>
> > > > > > CC:   [e-mail] <
> > > > > 
> > > > > [e-mail]>, Mahesh Jethanandani <
> > > > > [e-mail]>
> > > > > > 
> > > > > > 
> > > > > > 
> > > > > > Hi,
> > > > > > 
> > > > > > yangdump-pro is correct. Every other compiler missed it...
> > > > > > 
> > > > > > 9.10.2.  The identityref's "base" Statement
> > > > > > 
> > > > > >    The "base" statement, which is a substatement to the "type"
> > > > > >    statement, MUST be present at least once if the type is
> > > > > >    "identityref".  The argument is the name of an identity, as
> > > 
> > > defined
> > > > > >    by an "identity" statement.  If a prefix is present on the
> > > 
> > > identity
> > > > > >    name, it refers to an identity defined in the module that was
> > > > > >    imported with that prefix.  *Otherwise, an identity with the
> > > 
> > > matching
> > > > > name MUST be defined in the current module or an included submodule.*
> > > > > > 
> > > > > > Using [e-mail] and [e-mail]
> > > > > > 
> > > > > > When I change 'natp44' to 'nat:natp44' in both when-stmts:
> > > > > > 
> > > > > > andy@andy-homedev:~/Desktop/FD1289/IETF$ yangdump-pro
> > > > > 
> > > > > [e-mail] modpath=.
> > > > > > 
> > > > > > *** /home/andy/Desktop/FD1289/IETF/[e-mail]
> > > > > > *** 0 Errors, 0 Warnings
> > > > > > 
> > > > > > andy@andy-homedev:~/Desktop/FD1289/IETF$
> > > > > > 
> > > > > > 
> > > > > > Andy
> > > > > > 
> > > > > > 
> > > > > > On Sat, Nov 18, 2017 at 11:07 AM, Benoit Claise <[e-mail]
> > > > > 
> > > > > <mailto:[e-mail]>> wrote:
> > > > > > 
> > > > > >     Hi Andy,
> > > > > > 
> > > > > >     Can you please have a look at [e-mail] at
> > > > > 
> > > > > http://www.claise.be/IETFYANGPageCompilation.html <
> > > 
> > > http://www.claise.be/
> > > > > IETFYANGPageCompilation.html> .
> > > > > >     yangdump-pro reports a new error, while the other validators are
> > > > > 
> > > > > fine.
> > > > > > 
> > > > > >     Copying Mahesh, as YANG doctor.
> > > > > > 
> > > > > >     Regards, Benoit
> > > > > > 
> > > > > > 
> > > > > > 
> > > > > 
> > > > > 
> > > > > 
> 
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-- 
Ladislav Lhotka
Head, CZ.NIC Labs
PGP Key ID: 0xB8F92B08A9F76C67