From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mark H Weaver <mhw@netris.org>
Subject: Re: hydra.gnu.org now provides substitutes for =?utf-8?B?4oCYZ3Vp?=
	=?utf-8?B?eCBwdWxs4oCZ?=
Date: Wed, 07 Nov 2018 19:03:36 -0500
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In-Reply-To: <20181107081909.x734ulafjlnzo2rv@thebird.nl> (Pjotr Prins's
	message of "Wed, 7 Nov 2018 09:19:09 +0100")
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To: Pjotr Prins <pjotr.public12@thebird.nl>
Cc: guix-devel@gnu.org

Hi Pjotr,

Pjotr Prins <pjotr.public12@thebird.nl> writes:

> Another thing I find a little strange. When I install a package or an
> environment it completes fine. When I add then --no-substitutes flag
> and it always builds stuff like openssl and libgcrypt, pango and such
> from source.
>
> I.e., it creates a build system (I suppose). If the install is
> complete it should not have to do that. 
>
> Even if I do 
>
>   guix environment -C guix
>
> (which should include a build system, right?) and after completion
> run the same with --no-substitutes it starts to build right away.
>
> Any thoughts on that?

My first guess is that it has to do with grafting.  If I'm not mistaken,
in order to generate a graft derivation (.drv file), we need to know
which store items are referenced in the ungrafted outputs.  When
substitutes are enabled, Guix can get the lists of references from the
substitute servers.  When --no-substitutes is passed, and the ungrafted
outputs are not in the local store, they must be locally built in order
to determine the set of references.

Or at least that's my guess.  Ludovic could answer more definitively, as
he wrote the relevant code.

       Mark