It have been 3 months since last release of Mock. A lot of changes happened during summer.
Michal worked during GSoC on nofsync plugin and LVM support, which can significantly increase speed of Mock. He also rewrote some old code and prepared most of the code for Python3. Watch his blog for more details.
I reviewed all those changes and we tried to preserve the same functionality. But still - lots of lines in code have been moved. It may happened that we miss something.
Additionally I worked on BZ 1132762 - Support systemd-nspawn as a chroot replacement for mock. It worked for me. But during testing I find several problems. Therefore I decided to have this feature in code, but disable this by default. You can try it by passing --new-chroot to mock. It will use systemd-nspawn and do all building in container. Unfortunately it will break functionality like:
echo /usr/bin/ls | mock --shell
Right now it will work, because old chroot is used, but you can try:
echo /usr/bin/ls | mock --new-chroot --shell
and it will not work. It is very likely that usage of systemd-nspawn will be default in future and this behavior will stop working. You are encouraged to rewrite this code like this:
mock --chroot /usr/bin/ls
Because of Michal work, we had to change API for plugins. If you have your own plugin for Mock, it may need some changes. All internal Mock plugins have been altered. That new LVM plugin have been put in separate subpackage named mock-lvm and because of missing requirements is not available on RHEL6.
To sum it up: there is big changes and pretty high chance for regressions. Therefore we decided to bump up major number in version and not release for stable Fedoras and RHELs (as it can cause disruption of Koji). If you want to test this release, you can use rawhide or Copr repository. I repeat: do not use this version for production. On the other hand, if you use mock in your scripts or application, then please test it and report issues, so we can be confident that next release is really stable.