[yang-models] Importing other modules sometimes break libyang backlinks

[ghooo]

Description

Importing other modules sometimes break libyang backlinks, which results in break DPB and generic-config-updater unit-tests in sonic-utilities

The build fails and the author of YANG model end up commenting out the the import and also removing the corresponding YANG validation.

Example from sonic-bgp-neighbor.yang

import commented

    // Comment sonic-vlan import here until libyang back-links issue is resolved for VLAN leaf reference.
    //import sonic-vlan {
    //    prefix vlan;
    //}

validation commented

                leaf neighbor {
                    type union {
                        type inet:ip-address;
                        type leafref {
                            path "/port:sonic-port/port:PORT/port:PORT_LIST/port:name";
                        }
                        type leafref {
                            path "/lag:sonic-portchannel/lag:PORTCHANNEL/lag:PORTCHANNEL_LIST/lag:name";
                        }
                       // Comment VLAN leaf reference here until libyang back-links issue is resolved and use VLAN string pattern
                       // type leafref {
                       //     path "/vlan:sonic-vlan/vlan:VLAN/vlan:VLAN_LIST/vlan:name";
                       // }
                        type string {
                            pattern 'Vlan([0-9]{1,3}|[1-3][0-9]{3}|[4][0][0-8][0-9]|[4][0][9][0-4])';
                        }
                    }
                    description "BGP Neighbor, it will be neighbor address or interface name";
                }

The issue can be found in multiple YANG files, retrieve them by: https://github.com/Azure/sonic-buildimage/search?q=back-links+issue

I believe existing backlinks might be broken for some models, as the unit-tests are not covering all cases

Steps to reproduce the issue:

1. edit sonic-bgp-neighbor.yang
2. uncomment the import and the validation
3. submit a PR, and wait for build

Describe the results you received:

Unit-tests failure in DPB and generic-config-updater unit-tests from sonic-utilities repo

Describe the results you expected:

Unit-tests to pass

[venkatmahalingam]

@praveen-li We commented few YANG fields to avoid the build failures in the past as we had the issue with the libyang back-links code, please update the latest on this, do we have any solution to the libyang backlinks issue and we can uncomment the YANG fields now?

// Comment sonic-vlan import here until libyang back-links issue is resolved for VLAN leaf reference.

[zhangyanzhao]

not blocking issue

[praveen-li]

• @li-pingmao

[zhangyanzhao]

Need @li-pingmao help to fix #9136

[zhangyanzhao]

Praveen will talk to Ping internally.

[zhangyanzhao]

@li-pingmao would you please join next YANG meeting to provide an update? Thanks.

[ghooo]

Related PR: #9545

[li-pingmao]

@li-pingmao would you please join next YANG meeting to provide an update? Thanks.

Yes, I will join this Thursday's meeting

[zhangyanzhao]

@li-pingmao need your help to update on this. Thanks.

[Blueve]

@zhangyanzhao @qiluo-msft @ganglyu this issue has lasting for long time.
We need triage this issue, otherwise we cannot have a solid yang validation