[bug#53466] [PATCH v2] home: Add redshift service.

[Andrew Tropin]

On 2022-02-01 09:43, Ludovic Courtès wrote:

> Hi,
>
> Andrew Tropin <andrew@trop.in> skribis:
>
>> On 2022-01-30 16:11, Ludovic Courtès wrote:
>>
>>> * gnu/home/services/desktop.scm: New file.
>>> * gnu/local.mk (GNU_SYSTEM_MODULES): Add it.
>>> * doc/guix.texi (Desktop Home Services): New node.
>
> [...]
>
>> Probably, I already mentioned, but combining renamed option names from
>> the configuration record and option names in the escape hatch is
>> inconsistent, confusing and error-prone.
>
> I think I replied already.
>
>> It's very unclear where this extra-content goes and user can't know it
>> until he check out the implementation or build the config (currently
>> it's also almost impossible to find it on file system after build).
>
> (He or she.)  I documented it in a way that I thought was clear:
>
>   @item @code{extra-content} (default: @code{""}) (type: 
> raw-configuration-string)
>   Extra content appended as-is to the Redshift configuration file.  […]
>
> Notice “appended”.  How would you phrase it?

(:

>> Using such type of escape hatch is no joy at all.
>
> Escape hatches are meant to be used as a last resort; they’re a hack.
> Normally, people would have everything they need with the provided
> bindings.  So yes, using them is no fun, but that’s not a surprise IMO.
>
>> Seems this one is missplaced and should be go before [manual] section,
>> otherwise it won't be possible to set values of redshift section.  And
>> doing so will lead to very ugly:
>>
>> (extra-content "\
>> dawn-time=5:30
>> dusk-time=18:30
>> [geoclue2]
>> some-other-option=value
>> # Do I know that I'm in the middle of config file?")
>>
>> It will be especially ugly or even erroneous, when the target config has
>> a format, which uses identation.
>>
>> I didn't try it for redshift, but in many ini parser it's forbidden to
>> repeat sections with the same name.
>
> Ah, bummer.
>
> Another way to see it is that I should augment the bindings, maybe
> that’s what you’re getting at?  :-)

Sorry, not sure if I can translate your question correctly, so I won't
try to answer it, but will rephrase my statement to crarify what I mean:

The current implementation of escape hatch doesn't work (I can't set
missing options in redshift section, because extra-content added after
manual section begins, and I'm not sure if redshift's ini parser allows
to define a section with the same name a few times, Git for example
allows to do so, but it's more an exception).  There are a few ways to fix it:

1. Move manual section on top of redshift section, so the extra-content
will be added just after redshift section
2. Move extra-content before manual section to accoplish the same.
3. Use file escape hatch (as it done in some system services), which
will invalidate all the options set before and just place the content of
file field as a value of configuration.
4. Provide the bindings for other options (probably what you were asking).

>
> I can do that.
>
>>> +     #$(home-redshift-configuration-extra-content config)))
>>
>> A little offtopic:
>>
>> I know a number of system services, where the extra-content goes in
>> unexpected locations and overall behavior of escape hatch is unexpected
>> and incosistent with other escape hatches.  Some of the services has a
>> number of escape hatches in almost every nested record with different
>> names and behaviors.
>>
>> I'm relatively fresh Guix user and this part really confused me at first
>> even having experience with NixOS module system before and it's very
>> likely that many people just don't report it, because it really hard to
>> get the roots of it.
>
> How does NixOS handle escape hatches today?  Back when I was using it is
> that it wasn’t any more consistent than what we have today, which is at
> least a consolation.

I don't remember, how it's done for nixos "system modules", but in
home-manager it's relatively consistent, in most cases it just a nested
maps (attrsets, a little more high-level analogue of alists):
https://rycee.gitlab.io/home-manager/options.html#opt-programs.git.extraConfig
https://rycee.gitlab.io/home-manager/options.html#opt-accounts.email.accounts._name_.msmtp.extraConfig
https://rycee.gitlab.io/home-manager/options.html#opt-gtk.gtk3.extraConfig

Sometimes, it allows to add a multi-line string to the end of the file:
https://rycee.gitlab.io/home-manager/options.html#opt-programs.abook.extraConfig

but it's getting deprecated, when proper serializer for target config
format is implemented:
https://github.com/nix-community/home-manager/blob/master/modules/programs/git.nix#L342

As you can see, they provide a list of frequently used options as
top-level "fields", but all of them, including extraConfig just extends
(get merged) to primary "config" (iniContent for git for example) and
after that, this primary "config" attributeset get serialized to the
target config file.  While they have this "escape hatch", it works the
same way as all other fields with the only difference: it doesn't have
schema (just untyped attributeset).  This is quite close to what we do
in rde.

-- 
Best regards,
Andrew Tropin

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