bug#22990: Grafts leads to inefficient substitute info retrieval

[ludo@gnu.org (Ludovic Courtès)]

Alex Kost <alezost@gmail.com> skribis:

> Ludovic Courtès (2016-03-11 19:52 +0300) wrote:
>
>> As of right now (v0.9.0-2007-g66a30a3), ‘graft-derivation’ works either by:
>>
>>   1. Fetching substitute info about the things being built so that it
>>      can determine its references, which in turns allows it to determine
>>      whether they need to be grafted.
>>
>>   2. Building stuff, as a last resort, so that it can determine its
>>      references.
>
> I noticed that #1 is happening even with --no-substitutes option.  Is it
> intended?

Not really, but I see this is because ‘substitutable-path-info’ (called
from ‘references/substitutes’, called from ‘graft-derivation’) works
regardless of whether substitutes are enabled:

--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> ,use(guix)
scheme@(guile-user)> (define s (open-connection))
scheme@(guile-user)> (set-build-options s #:use-substitutes? #f)
$2 = #t
scheme@(guile-user)> (valid-path? s "/gnu/store/qf2lm7jpiiyygxz8zq0r1ca1fazv6smn-mutt-1.5.24")
$3 = #f
scheme@(guile-user)> (substitutable-path-info s '("/gnu/store/qf2lm7jpiiyygxz8zq0r1ca1fazv6smn-mutt-1.5.24"))
$4 = (#<<substitutable> path: "/gnu/store/qf2lm7jpiiyygxz8zq0r1ca1fazv6smn-mutt-1.5.24" deriver: "/gnu/store/jcl9c3w463xa2g963q5a60rrd97y1g28-mutt-1.5.24.drv" refs: ("/gnu/store/3gmzl5jpk700hqyr8p3kfg0vgcnw8d97-libassuan-2.4.2" "/gnu/store/b02lmk67jq1vcflk2m2bwzc8gmwmndqp-ncurses-6.0" "/gnu/store/d3xdc2w87yw3raafwb9q34gxx4xqci8k-cyrus-sasl-2.1.26" "/gnu/store/pkasxagsa4z4viscfpl6sjszmdmwncl1-gcc-4.9.3-lib" "/gnu/store/qf2lm7jpiiyygxz8zq0r1ca1fazv6smn-mutt-1.5.24" "/gnu/store/qvx4q6lbwi4s3cwr8wqaa7kcva0a5c4b-openssl-1.0.2f" "/gnu/store/sb40mddkia0brc814xkbnhxccfm32q3a-gpgme-1.6.0" "/gnu/store/sgzfawy95pfn7nsw3xvmca58llm5zzbc-glibc-2.22" "/gnu/store/x2p2biyybcb2wac77qz9468asc5fm48i-perl-5.22.1" "/gnu/store/x8dmdlrn5qn0wrbcnngj55y3ab73h0pp-bash-4.3.42" "/gnu/store/zpxg45dq67psrn4wmfk4l635h0si8q63-libgpg-error-1.21") dl-size: 0 nar-size: 6661016>)
--8<---------------cut here---------------end--------------->8---

However, substitutes are not downloaded, so in this regard
--no-substitutes is honored.

Ludo’.