[aur-general] PKGBUILD that helps with VCS upstream contribution?

[Philipp]

One of the reasons why I like Arch Linux so much is that it makes it
easy to work together with upstream. Through makepkg I can install the
latest, even VCS, version in a sane and very comfortable way.

So far I've mainly been testing, reporting bugs, stuff like that, but
rarely needed to contribute any code.

Now if I wanted to contribute code back to a project that uses git, how
would I do that without losing the comfort and safety of makepkg?
I figured it should be possible to write a PKGBUILD that gets the latest
upstream changes but also integrates local changes.

Sadly both my bash and git skills are minimal, so I was wondering if
someone already has such a PKGBUILD, for git at least and maybe for svn
as well.

TIA
-- 

Regards,
Philipp