Guix packaging tutorial with hand holding

[白い熊]

Hi Guix:

I'd like to advance step-by-step in learning how to write package definitions 
with the eventual goal of contributing to Guix.

For this I'd like to ask if someone could help me and other 
Guix-hacking-packaging beginners with some hand holding — concrete though, with 
examples, so I could then proceed through trial and error.

I've tried to follow the Guix packaging tutorial guide [1]. I can build and 
install the sample my-hello package with the from-file approach.

Next, I'd like to build and install the sample my-libgit2 package. Here, 
however I can't proceed:

The tutorial is old so it mentions the “GUIX_PACKAGE_PATH” approach which is 
deprecated and recommends using Guix channels. In the Guix manual I see the way 
to add a channel to your Guix, now is there a way to use a local git directory? 
So that I could experiment locally — without right away going through syncing 
the local git with an online git repository? If not I'll guess I'll have to go 
through Github just to play with some intro stuff.

Second, working on the Guix git checkout is recommended as the best way. What 
is the way of working with Guix git checkout on a GuixSD system? I.e. should I 
pull, build it — the git. Then what? Where to run guix pull and guix package -u 
— in the git, leave the SD versions un-updated?

Finally, are there some nice examples of using inheritance? I.e. I just want to 
add a compile option, or some dependency to some package — is there some 
example I can play with?

Many thanks for any help! :@)

[1] https://www.gnu.org/software/guix/blog/2018/a-packaging-tutorial-for-guix/

--
 Best regards / 宜しく御願い致します / S pozdravem / C уважением / Z poważaniem /
 Mit freundlichen Grüßen

白い熊