Re: Rethinking propagated inputs?

[Liliana Marie Prikler <liliana.prikler@gmail.com>]

Hi,

Am Donnerstag, den 09.09.2021, 00:12 +0200 schrieb Ludovic Courtès:
> Hi,
> 
> Maxime Devos <maximedevos@telenet.be> skribis:
> 
> > For packages using pkg-config, I had the following scheme in mind:
> 
> As a reminder to everyone, pkg-config is just one of the reasons for
> propagating inputs, probably not the main one numerically speaking.
That is true, pkg-config propagations are merely closest to the "core"
of Guix and thus (have the potential affect to) larger parts, whereas other forms are typically – though perhaps not necessarily – limited to some language ecosystem or similar.

> [...]
> It would be great if the ‘Requires’ field of .pc files could specify
> absolute file name; it would no longer be necessary to set
> PKG_CONFIG_PATH, and thus propagation wouldn’t be needed in this
> case.
In that regard, would symlinking other pkg-config files as proposed
somewhere in passing in [1] also work?  We would have to add a phase,
that parses the Requires field from installed pkg-config files, and
then symlinks the respective files from the inputs to gnu-build-system, 
but since they would then exist in PKG_CONFIG_PATH and point to the
library in question, theoretically we could get around this limitation
of pkg-config without requiring propagation.

> Regarding outputs, Nixpkgs introduced a “dev” output a while back
> that lumps together our “lib” and “include” outputs, roughly.  I
> think that’s a good idea (for other reasons too).
Naming-wise I'd still prefer the more concrete “lib” as “dev” to me is
a weird umbrella term that doesn't really tell me what I'm getting
(also it probably contributes to the distinction of users and devs, and
as some distros like Debian have demonstrated often becomes
pointless[2] the minute you introduce language bindings which require
dev inputs anyway).  

As far as the lib/include split in Guix is concerned, there appear to
be few packages that split them, so “lib” effectively is “dev” in Guix
when “out” isn't.  So apart from those outliers, is there something our
“lib” outputs are missing that Nix' “dev” outputs include?

Regards

[1] 
https://yhetil.org/guix-devel/997473f47b882a670e4b9bf6fe3fc66e66ba6911.camel@gmail.com/
[2] Pointless in the sense, that “users” need to install those “dev”
packages anyway if an application requires them.  Consider for example
a Guile application built on guile-git, which therefore requires
libgit2-dev to be installed.