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From: ludo@gnu.org (Ludovic =?utf-8?Q?Court=C3=A8s?=)
Subject: Re: Proposal: prefetch tarballs in a batch
Date: Sun, 13 Apr 2014 00:44:02 +0200
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In-Reply-To: <87ioqe2tdg.fsf@karetnikov.org> (Nikita Karetnikov's message of
	"Sun, 13 Apr 2014 00:19:23 +0400")
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To: Nikita Karetnikov <nikita@karetnikov.org>
Cc: guix-devel@gnu.org

Nikita Karetnikov <nikita@karetnikov.org> skribis:

>>> 1. Should the recursion stop when =E2=80=98fixed-output-derivation?=E2=
=80=99 returns #t?
>
>> I think so.  In general fixed-output derivations are the things you
>> would like to pre-fetch; so you would typically call =E2=80=98build-deri=
vations=E2=80=99
>> on these to do the actual pre-fetching.
>
> Could you show a package with a fixed-output derivation?  My current
> implementation calls itself indefinitely because the base case is never
> satisfied.

Any =E2=80=9Corigin=E2=80=9D that has no patches/snippet is a fixed-output =
derivation.

But!  There was a bug in =E2=80=98fixed-output-derivation?=E2=80=99 (which =
was actually
unused until now.)  Fixed in 99e17dc:

--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> (package-source-derivation s (package-source wget))
$12 =3D #<derivation /gnu/store/f96502xhla1k3daikjckn2zb1l17m8r5-wget-1.15.=
tar.xz.drv =3D> /gnu/store/qz9vm8802v6pi69ci2kgnvfivrkr085r-wget-1.15.tar.x=
z 2d1e730>
scheme@(guile-user)> (fixed-output-derivation? $12)
$13 =3D #t
--8<---------------cut here---------------end--------------->8---

Thanks!

Ludo=E2=80=99.