Re: Add the git commit id to the generation information

[Ricardo Wurmus <rekado@elephly.net>]

Hi Roel,

> I have a feature request.
>
> When I run 'guix pull', install a package, run 'guix pull' again (on
> another day), and install another package, I'd get two generations:
>
>> Generation 181  May 22 2017 11:47:37
>>  + haunt        0.2.1   out     /gnu/store/x2bkpzrdbaxavl29r2xg0fip1jjici9q-haunt-0.2.1
>>
>> Generation 182  May 24 2017 09:52:06    (current)
>>  + guile-commonmark     0.1     out     /gnu/store/k8vq65czfb8k4hvvjvsca34scd9xsxik-guile-commonmark-0.1
>
> Now, if I'd like to go to the Guix packages source code of generation
> 181, I can only guess at which actual state of the Guix repository this
> was, because this timestamp is the timestamp of creating the generation,
> not the timestamp of the Guix package state.  So, I'd like to propose to
> add the commit id to the generation like so:
>
>> Generation 181  May 22 2017 11:47:37    (ae548434337cddf9677a4cd52b9370810b2cc9b6)
>>  + haunt        0.2.1   out     /gnu/store/x2bkpzrdbaxavl29r2xg0fip1jjici9q-haunt-0.2.1
>>
>> Generation 182  May 24 2017 09:52:06    (current)
>>  + guile-commonmark     0.1     out     /gnu/store/k8vq65czfb8k4hvvjvsca34scd9xsxik-guile-commonmark-0.1

What would be the expected behaviour in the presence of
GUIX_PACKAGE_PATH?  I could have had GUIX_PACKAGE_PATH set pointing to a
module containing a custom variant of haunt.

I do agree that it would be very useful to know more about the state of
Guix for any given generation.  However, that state is more complex than
a single commit.

--
Ricardo

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