Handle environments when upgrading across a minor version bump

[davidanthoff]

This suggestion comes from here.

I think one option would be that if juliaup update detects an update that increases the minor version of Julia, that it copies the older environment file to the new Julia minor version. I think I would limit it to this scenario, i.e. not do anything with downgrades or stuff like that.

One question is whether just copying the env is actually a good user experience? Or would we have to instantiate, build or do other things as well?

[lungben]

I think that it would be good to instantiate the environment, too, so that the user is ready to use it.

Restricting to upgrades is fine for me, for downgrades one might run into issues with dependencies requiring newer Julia versions.

[davidanthoff]

I guess one other question, though, is whether this wouldn't be better handled in Julia itself? Not sure...

[davidanthoff]

I think at the end of the day this would be better handled in Julia itself. For example, if Julia 1.9.0 started, detected that no shared env for 1.9 exists, but there is one for 1.8, it could offer to migrate it, or something like that. But I do think this belongs into Julia, not Juliaup.