That is a mistake; there's no reason it can't be listed as a regular input.

During my tests to confirm this, I realized that sbcl-cl-rdkafka
wasn't actually producing any useful output. This led me down a
rabbit-hole (albeit a productive one). Below is a new patch set.

11:23 kate says: guix refresh -l sbcl-lparallel
Building the following 4 packages would ensure 8 dependent packages
are rebuilt: ecl-cl-rdkafka@1.0.2 cl-rdkafka@1.0.2
cl-random-forest@0.1-0.85fbdd4 next@1.5.0

All dependent packages continue to build.

On Fri, Jun 5, 2020 at 9:01 AM Guillaume Le Vaillant <glv@posteo.net> wrote:
>
>
> Hi,
>
> Katherine Cox-Buday <cox.katherine.e@gmail.com> skribis:
>
> > (propagated-inputs
> >  `(("librdkafka" ,librdkafka)))
>
> Why is the librdkafka library a propagated input instead of a regular
> input?