bug#57315: guix upgrade --dry-run output is basically useless

[Ludovic Courtès]

Hi,

zimoun <zimon.toutoune@gmail.com> skribis:

> Just to mention this report is somehow a duplicate of bug#40612 [1].
> Maybe, they could be merged.  WDYT?

Yes, please.

>> (If you’re curious, see
>> <https://guix.gnu.org/en/blog/2020/grafts-continued/> for details.)
>
> Nice read!  Quoting:
>
>         [...] do a first pass lowering packages to derivations as if
>         grafting was disabled, build all these derivations, and then do
>         a second pass to determine which packages in the graph need to
>         be grafted and to compute the relevant grafting
>         derivation. [...] If we reify that second pass to the user
>         interface code, it also addresses the user interface issue by
>         allowing it to display, possibly, two build plans: the
>         “ungrafted” one followed by the grafted one.
>
> Currently, these 2 plans are not well-exposed, IMHO.

When there are two or more passes, each one is printed as soon as
possible.  So you see “X MiB will be downloaded” or similar messages in
the middle of the process.

> $ guix package -i opensurge --dry-run
> guix package: warning: Your Guix installation is 12 days old.
> guix package: warning: Consider running 'guix pull' followed by
> 'guix package -u' to get up-to-date packages and security updates.
>
> The following package would be installed:
>    opensurge 0.5.2.1
>
> substitute: updating substitutes from 'https://ci.guix.gnu.org'... 100.0%
> substitute: updating substitutes from 'https://bordeaux.guix.gnu.org'... 
> 100.0%
> The following derivation would be built:
>   /gnu/store/r89hmhbxwm3gs1jl2dhns7gnwvi2k6s1-opensurge-0.5.2.1.drv
>
> 42.1 MB would be downloaded
>
> What does it mean?

That you’ll download 42M of dependencies and then build opensurge.

“The following derivation would be built” is about building derivations
that are not grafts.  For grafts, you would see “The following graft …”,
and only at verbosity level 2 or more (see ‘show-what-to-build’).

[...]

> When I run the option ’--dry-run’, I accept to pay a bit more and then
> compute as much as possible of derivations to have the most complete as
> possible graph to know beforehand and as accurately as possible:
>
>  1. what I need to download as substitutes
>  2. what I need to compile from source
>  3. what require grafts, e.g.,
>
>         require 1 graft for openal-1.20.1 ...
>         require 4 grafts for sfml-2.5.1 ...
>         require 6 grafts for mars-0.7.5.1.c855d04 ...
>
> Sometime, the plan looks exactly like that.  Sometime, it is really
> confusing and you have unpleasant surprises when running it.

By definition, the whole plan cannot be known in advance in the presence
of dynamic dependencies such as grafts, so it’s hard to do better.

The way it’s implemented right now is not optimal strictly speaking in
that we might bail out before we have a complete picture of everything
that’s known statically beforehand.  In practice though I think it’s
doing an okay job from that perspective.

Cheers,
Ludo’.