From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?utf-8?Q?Ludovic_Court=C3=A8s?= <ludo@gnu.org>
Subject: Build systems and implicit inputs
Date: Tue, 21 Jan 2020 11:56:18 +0100
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In-Reply-To: <871rry10ow.fsf@ambrevar.xyz> (Pierre Neidhardt's message of
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To: Pierre Neidhardt <mail@ambrevar.xyz>
Cc: Guix Devel <guix-devel@gnu.org>

Hi!

Pierre Neidhardt <mail@ambrevar.xyz> skribis:

> But as I understand it, all the "configurable part" of the builder is
> expose through the #:arguments field.  A simple example of this is
> python: the python-build-system has an argument which allows the package
> to specify whether we use python-2 or python-3.
>
> In this case, it's trivial to use parameters to influence which compiler
> the build system will use.
>
> For gnu-build-system (with gcc, clang, etc.) we can probably do similar
> things already by setting CC.
>
> The solution to your problem in my opinion is simply to expose just the
> right amount of options through #:arguments for all build systems.
> Would that be satisfactory to you?

I think the issue of tweaking the build system and its implicit inputs
must be addressed separately.  We first need a good API to do that.
When we have it, it=E2=80=99ll be nice and easy to drive it via package
parameters.  :-)

Currently each build system has ad-hoc keyword parameters to customize
its implicit inputs: #:python for =E2=80=98python-build-system=E2=80=99, #:=
cmake for
=E2=80=98cmake-build-system=E2=80=99, #:implicit-inputs? for =E2=80=98gnu-b=
uild-system=E2=80=99, etc.

For each of them, it would be quite easy to provide a procedure that
takes a list of implicit inputs and returns a <build-system>.  It may
not be all that convenient, and perhaps a bit too ad-hoc still.

Another option would be to make implicit inputs a field of
<build-system>.

Needs more thought!

Ludo=E2=80=99.