support external module requirements

[abierman]

There is no way in YANG to express a module dependency besides the "import" statement. This does not support 2 common use-cases:

• iana-if-type (used with ietf-interfaces but not imported)

• augment (augmented module never imports anything from the augmenting module)

Possible solution could be a new statement

requires { // could have SEMVER info specifying acceptable versions }

In order to support placeholder modules and flexible dependency chains, virtual modules could be supported, similar to Yocto

module A { requires routing; ...

}

module ietf-routing { provides routing; ... }

[tonydamage]

@abierman: This is more how you are looking at issue:

• augment - you could think of that statement is actually importing a subtree from imported module and modifing it.

• iana-if-type - In this case it is specified in iana-if-type that it imports ietf-interfaces. I can image having use ietf-interfaces without iana-if-type.

[mbj4668]

Isn't this solved with packages (#50)?

[kwatsen]

Andy: maybe this is more a YANG-library or a YANG-package issue.

Closed in Feb 6 Virtual Interim meeting.