Re: hard dependency on Git? (was bug#65866: [PATCH 0/8] Add built-in builder for Git checkouts)

[wolf <wolf@wolfsden.cz>]

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On 2023-09-11 17:17:24 +0200, Simon Tournier wrote:
> Hi,
> 
> On Mon, 11 Sep 2023 at 16:23, Ludovic Courtès <ludo@gnu.org> wrote:
> 
> > Note that the patch series adds a hard dependency on Git.
> > This is because the existing ‘git-fetch’ code depends on Git,
> > which is itself motivated by the fact that Git supports
> > shallow clones and libgit2/Guile-Git doesn’t.
> 
> Going this path, I appears to me worth to revisit the proposal:
> 
>         RFC: libgit2 is slow/inefficient; switch to git command?
>         Maxim Cournoyer <maxim.cournoyer@gmail.com>
>         Mon, 21 Nov 2022 21:21:02 -0500
>         id:87cz9fpw4x.fsf@gmail.com
>         https://yhetil.org/guix/87cz9fpw4x.fsf@gmail.com
>         https://lists.gnu.org/archive/html/guix-devel/2022-11
> 
> I know it is not an option for now to parse the output of ’git’ commands
> in order to keep the features of (guix git), (guix channels), etc.
> 
> However, this discussion was mentioning an implementation of
> clone/checkout in pure Racket supporting shallow checkout.  Considering
> the current level of integration, I thought the next Big Plan™ was to
> gradually move bits of Guile-Git to being pure Scheme, maybe based on
> the Racket implementation of ’clone’ as a starting point.
> 
> Personally, I do not have a strong opinion about the Big Plan™.  I note
> that the introduction of Git as a hard dependency is a slippery slope
> considering the current state of libgit2.  Here, it starts with “git
> clone”, then “git gc” (unsupported by libgit2) is also in the pipes
> (#65720 [1]).  And after timing, I am almost sure that many operations
> using Guile-Git will be slower than their plain Git counter-parts.  And
> we will start to parse the output of ’git’ plumbing commands.

If you don't mind me asking, why is that so problematic approach?  Git's
plumbing commands are intended to be used in scripts, so I am unsure what the
problem is.

I cannot recall a single instance when some tooling I have at home or wrote for
work stopped working due to git changing.  I guess there likely are such
instances, but would be interested in examples if someone has a list.

> Slippery slope for pushing Guile-Git out, no?

Guile-git does not seem to be in the best place currently, when I was putting
together the script I sent to #65720, I tried to use the info manual, and the
best way to describe it is "incomplete".  Some behaviors are... surprising.

Arguably that is the impression I got based on one morning of trying to use it,
so it is probably inaccurate description and lacks some details.

> 
> And I do not speak about the closure.  Is it possible to extract the
> command ’git-clone’ from git-minimal?  It would reduce the size, no?
> 
> 
> Cheers,
> simon
> 
> 1: https://issues.guix.gnu.org/65720
> 

-- 
There are only two hard things in Computer Science:
cache invalidation, naming things and off-by-one errors.

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