Re: Contributing Guix Home services

[Tanguy LE CARROUR <tanguy@bioneland.org>]

Hi Ludo’,


Quoting Ludovic Courtès (2023-04-17 15:39:02)
> Tanguy LE CARROUR <tanguy@bioneland.org> skribis:
> > It's been quite a journey on my side! Ups. Downs. Mostly downs, though! 😅
> > Thanks to Simon's unconditional technical and moral support, a **LOT**
> > has changed since I sent this message. Hopefully for the better! 🤞
> 
> Heh.  :-)  While it’s fresh on your mind, it would be nice to list the
> problems you ran into on your journey and see what we can do about it.

Mostly figuring out how to test it!

On my machine at home, `guix home reconfigure` can take minutes.
And some errors don't actually show up.
After trying different solutions, I eventually settled on the following:
while developing, I add, at the end of service file, something like:

```scheme
(define configuration
  (home-service-configuration
   ; […]
  )

(mixed-text-file
 "test"
 (serialize-configuration configuration home-service-configuration-fields))
```

And then I run:

```console
> cat (guix build -f path/to/home/service.scm)
# … the content of the generated file
```

I can only test file generation, though.

Then I painfully discovered that replacing in a string is not as easy as
it sounds, or, more precisely, that "python replace in string" yields
better results than "scheme replace in string" in DuckDuckGo!

I've also used `gexp` in places where I'm not sure it makes any sense,
but it works, so… #pragmatic!


> > At least now one of them [1] looks like a decent home service. Except
> > for the problem with `(every khal-calendar? lst)` that I haven't figure
> > out yet.
> >
> > [1]: https://git.easter-eggs.org/bioneland/guix/-/blob/main/bioneland/home/services/khal.scm
> >
> >
> > The one for MSMTP [2] does not contain all the available options, but all
> > the configurations and serializers are there.
> >
> > [2]: https://git.easter-eggs.org/bioneland/guix/-/blob/main/bioneland/home/services/msmtp.scm
> 
> I don’t use these two programs, but the services look nice!  The extra
> bit of work you’d have to do is documentation, similar to what is done
> for the other Home services.  Maybe start with msmtp to get a feel of
> what that entails?

`(configuration->documentation 'home-msmtp-configuration)`
`(configuration->documentation 'msmtp-account)`
`(configuration->documentation 'msmtp-configuration)`
… *et voilà !*


> >> There’s no formal rule, but I think that what we’ve been doing so far is to ensure basic functionality of
> >> the service is covered, and to provide an “escape hatch” for bits of the
> >> configuration that are not covered.
> >
> > If by "escape hatch" you mean `extra-config`, you're right!
> 
> Yup!

The convention seems to be `extra-content`, but you knew what I meant, right!? 😅


> > I'll try to submit a patch for one of the two mentioned above soon…ish!
> 
> Excellent, thanks!

Done! <https://issues.guix.gnu.org/62969>
I could have done a **lot** more with the documentation, but I wanted to
be sure to get the basic right first.

-- 
Tanguy