[bug#64746] [PATCH 2/2] scripts: time-machine: Error when attempting to visit too old commits.

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

Hi Simon,

Simon Tournier <zimon.toutoune@gmail.com> writes:

> Hi,
>
> Thanks Maxim for this improvement.
>
>
> On Tue, 15 Aug 2023 at 18:14, Ludovic Courtès <ludo@gnu.org> wrote:
>
>> Following your question earlier today on IRC, I realized that this would
>> unconditionally add a Git checkout update every time ‘time-machine’ is
>> started.
>
> Please note that if git.savannah.gnu.org is not reachable, then “guix
> time-machine” fails.
>
> Let start with the regular:
>
> $ guix describe
> Generation 26   Jul 12 2023 09:13:39    (current)
>   guix 4a027d2
>     repository URL: https://git.savannah.gnu.org/git/guix.git
>     branch: master
>     commit: 4a027d2b0ee68e39f21f6802a8cd1751d3065330
>
> $ guix time-machine --commit=4a027d2 -- describe
> Updating channel 'guix' from Git repository at 'https://git.savannah.gnu.org/git/guix.git'...
> substitute: updating substitutes from 'https://ci.guix.gnu.org'... 100.0%
> substitute: updating substitutes from 'https://bordeaux.guix.gnu.org'... 100.0%
> building /gnu/store/sg8ca36rlbh4il6jy8dk2gr33lxm4z8q-compute-guix-derivation.drv...
> Computing Guix derivation for 'x86_64-linux'... |
> substitute: updating substitutes from 'https://ci.guix.gnu.org'... 100.0%
> substitute: updating substitutes from 'https://bordeaux.guix.gnu.org'... 100.0%
> The following derivations will be built:
> [...]
> building profile with 1 package...
>   guix 4a027d2
>     repository URL: https://git.savannah.gnu.org/git/guix.git
>     commit: 4a027d2b0ee68e39f21f6802a8cd1751d3065330
>
>
> So far, so good.  Here all is cached and so on.  Now, let make
> git.savannah.gnu.org unreachable by tweaking some stuff.  Then,
>
> $ guix time-machine --commit=4a027d2 -- describe
> guix time-machine: error: Git error: failed to resolve address for git.savannah.gnu.org: Name or service not known
>

[...]

> The check if the requested commit is newer than the
> %oldest-possible-commit should use the Git history graph closure
> similarly as the authentication mechanism, no?
>
> And this check should come after checking the cache, no?

Interesting finding!  I think it'd make sense to raise this issue
separately and discuss its resolution there, too keep things focused and
discoverable :-).

-- 
Thanks,
Maxim