[bug#56768] [PATCH] gnu: engineering: Add qucs-s.

[Maxime Devos]

On 30-07-2022 08:59, Artyom V. Poptsov wrote:
> > ... as you have observed, things work even when they aren't propagated
> > (at least for qtbase etc., ngspice and octave have not yet been
> > tested).
> I usually put into "propagated-inputs" packages that provide some binary
> that the current package use in the runtime.
>
> So do you mean that I should rely only on "inputs" package property, and
> the inputs will be propagated anyway if they're in use by the package?
Yes to the first (at least in this case, propagation is sometimes hard 
to avoid), no to the second. Propagation happens only for 
propagated-inputs; however, if they are 'in use' by the package by 
ending up in the references, then the GC won't remove the store items. 
The GC and propagation are independent mechanisms.

> Less experimentally, the propagated- in propagated-inputs means only 
> that: propagation -- the dependencies are still installed even if they 
> aren't propagated, because the substitute* inserts a reference so the 
> GC knows to not delete it, the only difference is that the dependency 
> isn't automatically put in the profile when not propagating. 

Here, I meant with 'installed' = entry in /gnu/store is downloaded or 
built and kept, not 'added to ~/.guix-profile or equivalent' -- the 
latter is propagation.

> So the next time Qucs-S run it gets the paths from the configuration
> file.
>
> I changed the substitutions so Qucs-S will ignore the paths to Octave
> and NGSpice from the configuration and will always use the paths
> provided by Guix.  Also any custom paths to Octave and NGSpice will be
> overwritten in the config when the application exits.
>
> That is sub-optimal in my view as we're messing up with the application
> configuration logic and if a user wants to change those paths he or she
> will be able to remove the config and set the paths in the startup
> configuration dialogue, but the settings will have no effect; that will
> be a bit confusing.
>
> Yet at least Qucs-S will always use the right Octave/NGSpice path from
> GNU Guix.
>
> What do you think?
>
> Here's the patch.

It's not ideal that the ngspice cannot be overridden in the 
configuration, but OTOH we have --with-input. I think it's acceptable, 
though if there are any users that would like to override in the 
configuration, we might need to propagate it again and remove the 
substitute* -- or better, though more work: patch qucs-s to use the 
configuration when explicitly set by the user and don't write 
/gnu/store/... inside it automatically, with /gnu/store/... as a 
fallback when it is not set.

Greetings,
Maxime.

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