Repository: add a function to purge stale ports

[jmairboeck]

i.e. remove the work directories and downloads of old port (versions) which have been removed. A new command line option "--purge-stale-ports" is introduced for this.

To get the sources of ports (and thus which downloads to keep) it must parse all recipes.

Note that this may be a bit destructive if you are switching git branches while working on something!

[waddlesplash]

Doesn't the buildmaster do this? So there must be some mechanism for it somewhere already?

[OscarL]

Doesn't the buildmaster do this? So there must be some mechanism for it somewhere already?

I think builders only call RemoteBuilderSSH._purgePort() from RemoteBuilderSSH.runBuild(). That ultimately calls Port.purge(), but that works for only the given port, not for the whole tree, and not just for stale ports, as in this PR, AFAICS.

[jmairboeck]

Doesn't the buildmaster do this? So there must be some mechanism for it somewhere already?

I think builders only call RemoteBuilderSSH._purgePort() from RemoteBuilderSSH.runBuild(). That ultimately calls Port.purge(), but that works for only the given port, not for the whole tree, and not just for stale ports, as in this PR, AFAICS.

Yes, there is Port.purge(), but that only works for existing ports. This does the same for ports which don't exist any more.