Should increase in value space be considered NBC (or flagged separately) ?

[jsterne]

RFC7950 allows, amongst other things, the following changes as backwards compatible:

• adding a new leaf
• increasing the value space of a leaf (without changing the underlying type)

But a server being accessed by multiple clients may not be able to control newer clients from taking advantage of new leafs and increased value space. Older clients can ignore unknown leafs, but won't know how to handle values in the increased value space. The old clients should avoid falling over (i.e. should be able to receive the new values) but the applications that sit on top of that will likely cease to work correctly even though the changes were marked backwards compatible.

In the context of YANG 1.1 I don't think we can really decide to consider value space expansion as NBC (that's too far from RFC7950). But perhaps something for YANG 2.0 to consider ?

And maybe the tooling draft should report value space expansion as part of the output report (even if it is considered BC).