guide to migrating to virtdomains: userid

[ellie timoney]

On Wed, Jan 15, 2020, at 1:18 PM, Ricardo Signes wrote:
> *QUESTION:* Do we have an established policy for how features are deprecated and removed? For example, if we can make a backward incompatible change in Cyrus X.Y.0, how long in advance do we need to provide notice, and via what means?
> 
> In this case, the very least we can do is add it to the documentation. The second-to-least thing we can do is issue a warning when a deprecated setting is found, even if we don't have a timetable for removal.

[This is not really what you're asking, but we have a mechanism for deprecating config options. This looks like it's mostly been used so far for renaming options from badnameswithnounderscores to sensible_names. It's not quite useful here though: it deals with deprecating _entire options_, not merely "some values thereof".]

My longer term gut feel on this one (virtdomains:userid) specifically is: this time, we encourage (via good upgrade docs) people to consider switching to the only-known-good setting, but we change nothing. Next time, if we feel like the world is ready for it, we make the good setting the default (and the upgrade doc at that time will need to be clear that people who hadn't already migrated to it need to either a) migrate to it, or b) explicitly set their config to the value they may previously have had by default).

Historically, 3.0 changed the default values of unixhierarchyseparator and altnamespace. We talked a lot about it on the mailing lists, and the upgrade docs were clear about it. I think it may have caused some confusion, but I also think on the whole people mostly coped. But I guess maybe people coped by just setting the setting to whatever they were already using (rather than dealing with the changed behaviour). At one point, 3.0 documentation said the default value of virtdomains had changed too, but that didn't actually happen, and I think the bad documentation was identified and corrected during the beta process.

3.0 was a pretty massive upgrade from 2.x, though. 3.0->3.2 is, I think, a much smaller step, which might mean things go more smoothly, or might mean people are more cavalier about it and thus trip over stuff.
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