bug#40612: guix build system --dry-run is broken

["Ludovic Courtès" <ludo@gnu.org>]

Hello!

Björn Höfling <bjoern.hoefling@bjoernhoefling.de> skribis:

> On Mon, 13 Apr 2020 17:31:56 -0400
> Mark H Weaver <mhw@netris.org> wrote:
>
>> I guess this is related to the recent changes in graft handling, where
>> --dry-run (a.k.a. -n) no longer implies --no-grafts.  It's not working
>> well for me.  I hadn't updated my system since before those grafting
>> changes were made, and there's a lot for me to rebuild (I don't use
>> substitutes).  I was very surprised to see this small output:
>
> Hi Mark,
>
> I can confirm this behavior for "guix system". I'm on

Yeah, it has to do with the new build handler and the lack of
“parallelism” when building the system derivation:

  https://lists.gnu.org/archive/html/guix-devel/2020-03/msg00337.html

I think we’ll improve it over time by introducing more parallelism
there.

Fundamentally though, we have to understand that ‘--dry-run’ can only
print the first derivation plans, not those that are dynamically built
as a function of build results.

Thanks,
Ludo’.