[GSoC] migration

[Bradley Giesbrecht]

> On Jul 27, 2017, at 11:39 AM, db <iamsudo at gmail.com> wrote:
> 
> On 27 Jul 2017, at 00:35, Umesh Singla <umeshksingla at macports.org> wrote:
>> Hi Josh
>>> We don't have version dependencies so no, this sort of check is not possible a priori. Breakage will be caught by rev-upgrade after the fact in many cases (and if it is set to rebuild automatically, it may well revert you back to the newer version).
> 
>>> Also note that we can't actually revert to an older version of a port if it has been uninstalled.
> 
> Does it mean that snapshot just outputs a list of ports, deps and variants without their versions, so if I postpone the restore long enough, it'll reinstall current versions of all of them? I'm thinking here about the possibility of reinstalling a system or migrating between machines with same operating system and ending up with some broken ports.

Migration will uninstall all installed ports and then install all the ports from the snapshot (active and inactive) finishing with the same active ports and requested flags matching the snapshot. I imagine the order of install matters so that dependent ports are built first so the correct variants are active when the ports with dependencies build.

—
Brad