Always update version of pack when a new version is available

[robdimsdale]

When there is a new version of pack available but I already have a version installed under ./.bin/pack in an implementation buildpack, these scripts do not update pack to the newer version. I think they should.

I think there are valid arguments for not updating it, but I think it is simpler to know that we are always running against the latest version when we run integration tests

I think we would expand the logic in .util/tools.sh to run ./.bin/pack version and compare the versions.

I'm happy to submit a PR if folks agree this is worth doing.

[robdimsdale]

@paketo-buildpacks/tooling-maintainers thoughts?

If we implement auto-updating for pack I think we should also do it for jam, too.

[ForestEckhardt]

This idea sounds great to me! I am in favor of the idea.

[ryanmoran]

The only thing I would caution is that there have been instances in the past where the latest pack version contained a show-stopping bug that required us to roll back to a stable version. Would we want a flag to disable this auto-update feature?

[ForestEckhardt]

@ryanmoran I assumed that we would be just checking against tools.json to see that we have the version specified in that file. We could gate the releases that way. But if that is not the intention then I agree with your concern.

[robdimsdale]

@ryanmoran i didn't realize pack had released bugs/breaking changes of such severity in the past.

I think I would support @ForestEckhardt 's suggestion - always download the version in tools.json. That way if there is a bug it is easy to revert that file - both locally and by PRing to this repository.

While I haven't been burned by moving forward too quickly on pack, I have encountered issues where I forgot to upgrade my local copy of pack which caused issues.

[ryanmoran]

That seems fine to me. It wasn't clear that's what was suggested.