Re: Proposal: prefetch tarballs in a batch

[ludo@gnu.org (Ludovic Courtès)]

Nikita Karetnikov <nikita@karetnikov.org> skribis:

> So, in order to add a tarball to the store, one can write:
>
> $ ./pre-inst-env guile
> scheme@(guile-user)> ,use (guix store) (guix packages) (guix derivations) (gnu packages wget)
> scheme@(guile-user)> (define s (open-connection))
> scheme@(guile-user)> (package-source-derivation s (package-source wget))
> $1 = #<derivation /gnu/store/jf4hzf16akk7bjidpr6im3wamfnr5rpv-wget-1.15.tar.xz.drv => /gnu/store/qz9vm8802v6pi69ci2kgnvfivrkr085r-wget-1.15.tar.xz 1922cd0>
> scheme@(guile-user)> (build-derivations s (list $1))
> $2 = #t
> scheme@(guile-user)> (file-exists? (derivation->output-path $1))
> $3 = #t
>
> And to get a list of inputs (including the implicit ones):
>
> scheme@(guile-user)> ,use (srfi srfi-26)
> scheme@(guile-user)> (for-each (cut format #t "~a~%" <>) (derivation-inputs (package-derivation s wget)))
> #<<derivation-input> path: "/gnu/store/divcaakxh5zhgpkih3paxb6znmnpbzhw-guile-2.0.11.drv" sub-derivations: ("out")>
> #<<derivation-input> path: "/gnu/store/jf4hzf16akk7bjidpr6im3wamfnr5rpv-wget-1.15.tar.xz.drv" sub-derivations: ("out")>
> #<<derivation-input> path: "/gnu/store/rx5kn39gcc0vm4hwr81kcwpxgybx2yay-perl-5.16.1.drv" sub-derivations: ("out")>

Yup, but note that the you don’t need to actually build the derivation
to traverse it (IOW the ‘build-derivations’ call is not needed.)

> I’m planning to do the same for every input.  But a couple of things are
> not clear:
>
> 1. Should the recursion stop when ‘fixed-output-derivation?’ returns #t?

I think so.  In general fixed-output derivations are the things you
would like to pre-fetch; so you would typically call ‘build-derivations’
on these to do the actual pre-fetching.

> 2. I’d like to use ‘package-source-derivation’ (see above) in order to
>    get a tarball.  Is it possible to get a <package> type from
>    <derivation>?  If not, what are my options?

No: as the manual so nicely says ;-), “derivations are to package
definitions what assembly is to C programs.”

What I would imagine is something like:

  (define (derivations-to-prefetch store drv)
    "Return the list of fixed-output derivations that DRV depends on,
  directly or indirectly."
    ...)

And then you would just pass the result of this procedure to
‘build-derivations’, which would download anything not already present.

Does that make sense?

Ludo’.