feat: deduplicate tags

[bluebrown]

Signed-off-by: Nico Braun rainbowstack@gmail.com

resolve: #883

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[bluebrown]

I decided to move the logic to this place so that, it applies to all publishers.

I wanted to add some tests as well, but I didn't find a good way. This is because the publisher interface doesn't expose a way to get the tags. So it's hard to write a test to compare input and output tags.

[imjasonh]

(This isn't commentary on the PR exactly, just research notes I thought it would be useful to share)

The only place we care about the order of the tags is here:

ko/pkg/commands/resolver.go

Lines 241 to 246 in 140ac87

	if len(publishers) == 0 {
	// If one or more tags are specified, use the first tag in the list
	var tag string
	if len(po.Tags) >= 1 {
	tag = po.Tags[0]
	}

This is pretty esoteric. This happens if you're not publishing, but specify multiple tags. This might happen if you do:

ko build --tarball=foo.tar --push=false --tags=foo --tags=bar

In that case the tarball should have the foo tag applied consistently, and not bar.

While looking into this, I also found and fixed #885 which was just kinda weird.

[imjasonh]

This change LGTM, just needs a CLA before we can merge it.

[bluebrown]

I have accepted the CLA, and did the rescan :)

[imjasonh]

Ehh, I don't know if we need to bother with generics here, since we know we'll only call it with strings.

[bluebrown]

Yes, I had it only for strings before, but then I thought it may be useful for other stuff too. You mentioned platform, for example. Maybe that's also a string, not sure. I can change it, if you want, though.

[imjasonh]

Yeah I'd prefer to have it work on strings until/unless we find a generic use for it in the future. YAGNI and all.

[bluebrown]

ok done. I did a force push. Not sure how this is done here, but I know some project not doing squash merge and thefore prefer a single commit.