Prune versions not referenced in juliaup.json with --prune-orphans

[christiangnrd]

I took a look at #1129 and it seems like if a direct download channel was deleted and the .juliaup folder was not, it would forever be ignored by the gc command. I attempt to address it by adding a --prune-orphans flag similar to the --prune-linked flag that will remove any folder that starts with "julia-" that is not referenced by the "juliaup.json" config file.

Name is definitely open for suggestions, and I'd love suggestions to make my code more idiomatic. At the moment it feels clunky.

If this approach is accepted, I'll write a test.

I also added some clarifying comments to the SystemChannel code to make it easier to understand.

[ghyatzo]

#1153 could be related to this.
There seems to be some path normalization shenanigans going on. Have you ever encountered this?

Edit: It seems that removing a julia version that is currently open fails (understandably), but what happens is that even if the cleanup failed, the julia version is removed from the configuration file, making it orphan: See #1153 (comment)

Not sure if this should be a PR on its own or can be incorporated into this one, since we're touching the same code. Ideally we'd intercept the failed remove and other than printing an error, we also avoid deleting the version from the config, so that after calling juliaup gc like suggested actually does something.

And the error message could incorporate the hint that maybe there is that julia version open somewhere.

[christiangnrd]

Now that you mention it, I do remember noticing that while writing this PR, but with how busy the maintainers are, I try (emphasis on try) to make my PRs as easy to merge and with the least back and forth as possible.

I do think that’s a good idea though. If you tackle this yourself, maybe base it off this branch? Or feel free to open a new PR that replaces this one since I don’t know if this would be needed if old versions naturally get cleaned up from a regular juliaup gc invocation.

[christiangnrd]

Closing because #1205 was merged!