'do-release-upgrade -d' should always offer to upgrade to the most recent development release

[Mathew Hodson]

On Trusty, 'do-release-upgrade -d' is currently offering an upgrade to 14.10. It should offer to upgrade to Wily, because Wily is the current development release.

It makes sense if we are skipping versions for stable releases to also skip versions for development releases. The code in update-manager parses the meta-release files to determine which release to upgrade. As an example here is the meta-release-development entry for Utopic.

Dist: utopic
Name: Utopic Unicorn
Version: 14.10
Date: Thu, 23 Oct 2014 14:10:00 UTC
Supported: 0
Description: This is the 14.10 release
Release-File: http://archive.ubuntu.com/ubuntu/dists/utopic/Release
ReleaseNotes: http://changelogs.ubuntu.com/EOLReleaseAnnouncement
UpgradeTool: http://archive.ubuntu.com/ubuntu/dists/utopic/main/dist-upgrader-all/current/utopic.tar.gz
UpgradeToolSignature: http://archive.ubuntu.com/ubuntu/dists/utopic/main/dist-upgrader-all/current/utopic.tar.gz.gpg

We currently just check the date and supported status to determine to which release to upgrade, as the meta release files don't really contain information about whether or not a release is obsolete. If we are running with the -d switch we could check to see if the release date is greater than today. There should probably be a fudge factor of a day though as otherwise people may not be able to upgrade on release day.

[Brian Murray (brian-murray)]

We want to provide users the safest upgrade path from one release to another as such we going to keep it so that the '-d' switch will only take you to the development release of Ubuntu if you are running the release immediately before the development one. If testers want to test the upgrade path described in the description, from Trusty to Wily, then they can create a local version of the meta-release-development file with the desired from and to releases.