From mboxrd@z Thu Jan  1 00:00:00 1970
From: ludo@gnu.org (Ludovic =?utf-8?Q?Court=C3=A8s?=)
Subject: Re: package.scm: (profile-derivation (%store) '())
Date: Fri, 20 Sep 2013 23:35:09 +0200
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References: <87r4cjjsu2.fsf@karetnikov.org> <877gebdz2c.fsf@gnu.org>
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In-Reply-To: <87a9j7b3qq.fsf@karetnikov.org> (Nikita Karetnikov's message of
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To: Nikita Karetnikov <nikita@karetnikov.org>
Cc: guix-devel@gnu.org

Nikita Karetnikov <nikita@karetnikov.org> skribis:

>> =E2=80=98%store=E2=80=99 is a SRFI-39 parameter (info "(guile) Parameter=
s"), aka. a
>> dynamically-scoped variable.
>
>> It is initialized with the =E2=80=98parameterize=E2=80=99 form, which se=
ts its value for
>> the dynamic extent of its body.
>
> I don=E2=80=99t understand what code initializes =E2=80=98%store=E2=80=99.

This:

          (parameterize ((%store (open-connection)))
             ...)

> For example, I have one generation in the =E2=80=98test=E2=80=99 profile.=
  So =E2=80=98test=E2=80=99
> points to =E2=80=98test-1-link=E2=80=99.  If I do
>
> scheme@(guix scripts package)> (roll-back "test")
>
> I get an error
>
> guix/derivations.scm:428:17: In procedure derivation->output-path:
> guix/derivations.scm:428:17: In procedure struct_vtable: Wrong type argum=
ent in position 1 (expecting struct): #f
>
> Entering a new prompt.  Type `,bt' for a backtrace or `,q' to continue.
> scheme@(guix scripts package) [1]>=20

I suspect it=E2=80=99s the =E2=80=98%guile-for-build=E2=80=99 parameter tha=
t=E2=80=99s set to #f instead
of being set to a derivation here.  There=E2=80=99s also a =E2=80=98paramet=
erize=E2=80=99 form
for that one in guix/scripts/package.scm.

> But why does this command work?
>
> $ ./pre-inst-env guix package -p test --roll-back
> switching from generation 1 to 0

Because it=E2=80=99s designed to work!  :-)

> As far as I understand, this code is called when the above command is
> invoked:
>
>     ;; First roll back if asked to.
>     (if (and (assoc-ref opts 'roll-back?) (not dry-run?))
>         (begin
>           (roll-back profile)
>
> I don=E2=80=99t see any references to =E2=80=98%store=E2=80=99 here.

Look for =E2=80=98parameterize=E2=80=99; it=E2=80=99s dynamic scoping, whic=
h makes it less
visible.

HTH,
Ludo=E2=80=99.