Re: Rethinking propagated inputs?

[Maxime Devos <maximedevos@telenet.be>]

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Liliana Marie Prikler schreef op zo 05-09-2021 om 23:10 [+0200]:
> Am Sonntag, den 05.09.2021, 22:27 +0200 schrieb Maxime Devos:
> > Liliana Marie Prikler schreef op zo 05-09-2021 om 21:37 [+0200]:
> > > > > 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.
> > > 
> > > Is that so?  I would think the build process needs to see stuff
> > > outside of its inputs for that to work, e.g. the actual header it
> > > wants to include, which isn't part of "build".  Am I
> > > misunderstanding our sandbox requirements?
> > 
> > The .pc file includes the absolute path to the library and include
> > directories, so the output "build" with the .pc file has a reference
> > to the output "out" with the libraries and include headers.  More
> > concretely, take the .pc from the glib package:
> > 
> > prefix=/gnu/store/98hgv3i6hdqgiq98ldy7rkpdwhah8iq2-glib-2.62.6
> > libdir=${prefix}/lib
> > includedir=${prefix}/include
> > [more stuff]
> > Requires.private: libpcre >=  8.31
> > Libs: -L${libdir} -lglib-2.0
> > Libs.private: -pthread
> > Cflags: -I${includedir}/glib-2.0 -I${libdir}/glib-2.0/include
> > 
> > The (transitive) references of all inputs to the build process are
> > included in the sandbox.  In this case, if the package has the
> > hypothetical glib:build among its inputs, the daemon will
> > automatically make glib:out available as well in the sandbox.
> And IIUC if glib had a "lib" output, glib:lib would be available in the
> sandbox instead of glib:out due to the reference by glib:build?

If a package has the proposed 'glib:build' in its (propagated-)inputs,
and if 'glib' had a 'lib' output, then in the build sandbox of the package,
'glib:lib' will be available.

>   If
> that's the case using #:by and "build" outputs might be a preferable
> solution, if not for all packages then at least for some.

> At this point the question then becomes what to name this "build"
> output and what to put into it besides pkg-config stuff.  Particularly
> in the land of glib, there also exist typelibs, which can be used as
> "build" inputs in the case of Vala or as runtime inputs in the case of
> pygobject and other language bindings.  Perhaps this is early
> bikeshedding when we'd actually need to code up #:by, but what would be
> the better approach here?  Separate "build" into "pkg-config", "cmake"
> (for CMake-based package discovery), "typelib" etc. or have one more or
> less anonymous blob called "build"?

I don't know (-:.  Maybe let's just start with pkg-config and #:by?
for now?  The name can always be changed later.

Greetings,
Maxime.

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