Open Stack

Hi,

It turns out that there are some jobs in OpenStack's Zuul that were
relying on a behavior in devstack-gate and zuul-cloner that would check
out a tag when given an override branch.

Zuul v3 is a bit more literal -- the 'override-branch' option (for both
jobs and projects) will only checkout a branch, and if it does not
exist, it falls back in the usual manner.

To support this case we could:

1) Extend 'override-branch' to support tags as well as branches.

2) Add 'override-tag' to support tags.

3) Add 'override-ref' to support branches + tags.

We can of course do both 2 and 3 as well.

4) Add 'override-checkout' to support branches + tags.

If we do 3 (only), or 4, we might choose to drop 'override-branch'.

If we keep override-branch, we would need to establish whether more than
one of these options is permitted, and if so, what the order of
precedence is.  And if we declare them exclusive, what do to in the case
of inheritance.

I'm inclined to do the following:

Add 'override-checkout' to support branches + tags and drop (after a
deprecation period) 'override-branch'.  It's very clear what it does,
and it relates to git terminology.

Are there any other use cases (either in OpenStack or from other users)
that we should consider that might suggest we should choose another
solution?  And are there any other suggestions for how we might handle
this?

Thanks,

Jim