On Wed, Oct 1, 2025 at 12:56 AM Phú Liên <[email protected]> wrote:
> Hi RFC 8791 authors,
>
> I have a question regarding YANG data structure extensions (RFC 8791) and
> the use of augment-structure. Specifically, is it possible to augment the
> root of a YANG data structure?
>
> For example, with the YANG model below, yanglint validates successfully if
> the last "sx:augment-structure /foo:mystruct" statement is commented out.
> However, if that statement is included, yanglint reports an error:
>
> * Yang model
>
> ```
> module foo {
> namespace "foo";
> prefix foo;
>
> import ietf-yang-structure-ext { prefix sx; }
>
> sx:structure mystruct {
> container mycontainer {
> leaf leaf1 {
> type string;
> }
> }
> }
>
> sx:augment-structure /foo:mystruct/foo:mycontainer {
> leaf leaf2 {
> type string;
> }
> }
>
> // Augment to the root of the structure, so `leaf3` will be a sibling of
> `mycontainer`.
> sx:augment-structure /foo:mystruct {
> leaf leaf3 {
> type string;
> }
> }
> }
> ```
>
> * Yanglint error
>
> ```
> libyang err : Augment extension target node "/foo:mystruct" from module
> "foo" was not found.
> (/foo:{extension='sx:augment-structure'}/{augment='/foo:mystruct'})
> ```
>
> Moreover, if we cannot use augment-structure to add augments to the root
> of a structure, could you please suggest how to make the following leafref
> path valid in the YANG model below?
>
>
I do not see any text in RFC 8791 that prohibits augmenting the structure.
A valid path argument is provided to the extension.
sx:augment-structure /foo:mystruct
The structure 'mystruct' should be treated like a top-level NP container.
It shares the same namespace as real data-def-stmts.
Andy
* a.yang
>
> ```
> module a {
> namespace "urn:a";
> prefix a;
>
> import b {
> prefix b;
> }
> import ietf-yang-structure-ext {
> prefix sx;
> }
>
> grouping leafrefs {
> leaf leaf1 {
> type leafref {
> path "/a:top/a:leaf2";
> }
> }
> }
>
> grouping leaves {
> leaf leaf2 {
> type string;
> }
> }
>
> container top {
> config false;
> uses leaves;
> }
>
>
> // Augments 'a:leaf1' into '/b:mystruct/b:mycontainer'. This augmented
> // 'a:leaf1' will be a sibling of 'b:myleaf'.
> //
> // XPath within a structure can only reference nodes inside the same
> // structure. Therefore, '/a:top/a:leaf2' must also be augmented into
> // 'b:mystruct' to satisfy the leafref path.
> sx:augment-structure "/b:mystruct/b:mycontainer" {
> uses leafrefs;
> }
>
> // This 'augment-structure' attempts to satisfy the leafref path by
> augmenting
> // '/a:top/a:leaf2' into the root of '/b:mystruct'. However, yanglint
> reports
> // an error because we are augmenting to the root of a structure.
> sx:augment-structure "/b:mystruct" {
> container top {
> uses leaves;
> }
> }
>
> // This 'augment-structure' is valid in yanglint but does not satisfy the
> // leafref path because it augments '/b:top/a:leaf2', not
> '/a:top/a:leaf2'.
> sx:augment-structure "/b:mystruct/b:top" {
> uses leaves;
> }
> }
> ```
>
> * b.yang
>
> ```
> module b {
> namespace "urn:b";
> prefix b;
>
> import ietf-yang-structure-ext {
> prefix sx;
> }
>
> sx:structure mystruct {
> container mycontainer {
> leaf myleaf {
> type string;
> }
> }
> container top { }
> }
> }
> ```
>
> Yanglint reports the following error for the second augment-structure
> statement:
>
> ```
> libyang err : Augment extension target node "/b:mystruct" from module "a"
> was not found.
> (/a:{extension='sx:augment-structure'}/{augment='/b:mystruct'})
> ```
>
> And the following error for the third augment-structure statement:
>
> ```
> libyang err : Not found node "top" in path. (/b:mycontainer/a:leaf1)
> ```
>
> By the way, we found that this use of augment-structure is claimed to be
> supported in the following links:
>
> * https://docs.yumaworks.com/en/latest/yangauto/define-abstract-yang.html
> *
> https://dr2lopez.github.io/yang-provenance/draft-lopez-opsawg-yang-provenance.html
>
> BR/Phu
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