Changes to use cl-lib package were recently merged to master branch which means Emacs 24.3 is now the only version Magit works with out-of-the-box, for 24.2 and 24.1 one can apparently (I have only 24.3 so I haven't tested) get cl-lib via elpa (which was included in 24.1) and for 23.x you have to get either elpa (and then cl-lib using that) or cl-lib manually, assuming it works with 23.x.
Emacs 23.x is what is currently available in, for example, the latest Ubuntu releases (both the long term support version and the normal). I fail to see the benefits of the cl-lib transition outweighing the disadvantage of effectively dropping Emacs 23.x support at this point. I know cl is deprecated but it's going to be available for quite some time (as predicted by Stefan Monnier on Emacs developers' mailing list).
Regardless of my opinion about the transition, the documentation currently says "Magit supports GNU Emacs version 22 or later.", both in README.md and magit.texi. I think that should be updated if cl-lib requirement stays.
Hmm, it should be straightforward to fall back to cl if cl-lib isn't installed. If magit is installed using package.el it pulls in cl-lib automatically, but perhaps magit should something like:
(unless (require 'cl-lib nil t)
@Wilfred that won't work. The cl-lib functions have a cl- prefix, that's the whole point.
@azuk I don't see a reason why the forward compatibility cl-lib wouldn't work with 23 or 22. Please test and if you know for sure that cl-lib won't work with these versions let us know. @sigma has already enough to do merging incoming pull requests.
FWI I don't plan on dropping support for emacs 23.
And if possible I'd like to keep emacs 22. I'm aware of some problems right now (for example with epa) but these should be fixed before releasing.
@tarsius ah, my mistake, I'd misunderstood.
@sigma recently made some changes to better support 22. Closing as I think this is resolved now; if not reopen.