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From: =?utf-8?Q?Ludovic_Court=C3=A8s?= <ludo@gnu.org>
Subject: Re: 04/05: gnu: autoconf: Support cross-build.
Date: Tue, 21 Apr 2020 18:01:19 +0200
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To: guix-devel@gnu.org, Jan Nieuwenhuizen <janneke@gnu.org>

Hi!

guix-commits@gnu.org skribis:

> commit 6833403fb393a513c77aa3cb8fca7d57b87befe1
> Author: Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
> AuthorDate: Sat Apr 18 19:49:54 2020 +0200
>
>     gnu: autoconf: Support cross-build.
>=20=20=20=20=20
>     Autoconf cannot be cross-built properly: it lacks the concept of
>     <tool>-for-build.  It runs the host `autom4te' (a perl script) during=
 build.
>=20=20=20=20=20
>     * gnu/packages/autotools.scm (autoconf)[inputs]: When cross-building,=
 add perl
>     and m4.
>     [native-inputs]: when cross-building, use -for-build names.
>     [arguments]: When cross-building, add `fake-cross-build' phase to sub=
stitute
>     m4 and perl.

Thanks for fixing it!  Some comments:

> +    (inputs
> +     (if (%current-target-system)
> +         `(("perl" ,perl)
> +           ("m4" ,m4))
> +         '()))
>      (native-inputs
> -     `(("perl" ,perl)
> -       ("m4" ,m4)))
> +     (if (%current-target-system)
> +         `(("perl-for-build" ,perl)
> +           ("m4-for-build" ,m4))
> +         `(("perl" ,perl)
> +           ("m4" ,m4))))

You can remove the =E2=80=98if=E2=80=99 in both cases: we always need Perl/=
M4 both as a
native input and as an input in both cases.

However, that might trigger a rebuild, so perhaps you=E2=80=99ll have to le=
ave
the ifs, but with a TODO telling to remove it on the next rebuild or
Marius will be mad at us.

> +    (arguments
> +     `(#:tests? #f

Nope.  :-)

> +       ,@(if (%current-target-system)
> +             `(#:phases
> +               (modify-phases %standard-phases
> +                 ;; Autoconf cannot be cross-built properly: it lacks the
> +                 ;; concept of <tool>-for-build.  It even runs the host
> +                 ;; `autom4te' (a perl script) during build.
> +                 (add-after 'install 'fake-cross-build
> +                   (lambda* (#:key build inputs outputs #:allow-other-ke=
ys)
> +                     (let ((m4 (assoc-ref inputs "m4"))
> +                           (perl (assoc-ref inputs "perl"))
> +                           (out  (assoc-ref outputs "out")))
> +                      (substitute* (find-files (string-append out "/bin"=
))
> +                        (("/gnu/store/[^/]*-m4-[^/]*") m4)
> +                        (("/gnu/store/[^/]*-perl-[^/]*") perl))
> +                      #t)))))

Why is this needed?  The =E2=80=98patch-shebangs=E2=80=99 phase normally ta=
kes the
inputs, not the native inputs, when changing shebangs.

(You previously found that something=E2=80=99s wrong there, but I forgot wh=
at=E2=80=A6)

Thanks,
Ludo=E2=80=99.