Liliana Marie Prikler schreef op zo 05-09-2021 om 18:50 [+0200]:
> 
[...]
> > (Feel free to suggest a more concise name.)
> Since "propagated" is already given by propagated-inputs, what about
> simply having #:by?
> E.g. something like: [...]
>   (define glib
>     (package
>       (name "glib")
>       (outputs '("out" ; everything
>                  "bin")) ; glib-mkenums ... depends on Python
>       (propagated-inputs
>         `(("pcre" ,pcre #:by ("out"))     ; future-proof #:by  
>           ("libffi" ,libffi #:by ("out")) ; have it be a list
>           [...]))

That looks nice, thanks.

> I'm not sure whether we need to necessarily add a new "build" output
> for pkg-config, that'd lead to a lot of doubly-propagated includes. 
> (Imagine both libffi and libffi:build etc.)  I think the more
> meaningful division here would be to add "bin" or "lib" outputs to
> those packages, where we don't want propagation to continue
> indefinitely.

Putting pkg-config files into the "lib" or "out" output (together with shared libraries)
seems reasonable to me ("lib" if the package is usually used as a binary,
but also has libaries with pkg-config files, and "out" if it is usually
used as a library).

>   This does cause problems with language bindings though,
> e.g. pygobject, as those also propagate the package in question and
> can't be neatly separated.

python-pygobject can just keep everything in the output "out",
and let glib and libffi be propagated by "out", no?  I don't see
how this would cause trouble for language bindings.

> > Now, imagine the "build" output of "zile" had glib:build in
> > propagated-inputs, using the scheme described above.  Then, if the
> > "out" output of zile is installed in a profile, that doesn't cause
> > glib to appear in the profile as well, because glib
> > is only propagated for the "build" output of zile, and not for "out"
> > output of zile.
> > 
> > However, if "build" is installed in the profile (e.g. because someone
> > runs "guix environment --ad-hoc zile:build various compilation tools"
> > to create an application using the zile library), then the .pc
> > becomes available in the profile. 
> I must admit that this solution appears to have some surface elegance,
> but what exactly would go in the "build" output of a package?  You
> mentioned pkg-config files (obviously), but those don't suffice to
> actually build a package, do they?

Sometimes they do suffice.  The .pc files contain the "-L/.../LIB",
"-I/.../include" and "-lstuff" flags needed for compilation.  If the
build system of the package uses pkg-config, it will use those flags,
so the compiler will find the library in that case.

Not sure if they always do suffice.

>   Would we need an extra syntax to
> e.g. propagate the "out" output by "build" (and in some cases the "lib"
> output instead)?

Not if .pc files are put in "out" (or "lib" in some cases) instead of the
originally proposed "build", but otherwise, possibly?

Greetings,
Maxime.