Re: should git maintenance prefetch be taught to honor remote.fetch refspec?

[Tom Saeger <tom.saeger@oracle.com>]

On Thu, Apr 01, 2021 at 06:25:36PM -0400, Derrick Stolee wrote:
> On 4/1/2021 4:14 PM, Junio C Hamano wrote:
> > Derrick Stolee <stolee@gmail.com> writes:
> > 
> >> On 4/1/2021 2:49 PM, Tom Saeger wrote:
> >>> I've recently setup git maintenance and noticed prefetch task
> >>> fetches ALL remote refs (well not tags) and does not honor
> >>> remote fetch config settings.
> >>
> >> This is intentional. The point is to get the latest objects
> >> without modifying any local copies of refs. You still need
> >> to run "git fetch" manually to update the refs, but that
> >> should be faster because you have most of the objects already
> >> in your copy of the repository.
> > 
> > You answered only half of the question, I think.
> 
> You are right. Thanks, both, for pointing that out.
>  
> > The plain vanilla refspec after you clone would be
> > 
> >     [remote "origin"]
> > 	fetch = +refs/heads/*:refs/remotes/origin/*
> > 
> > and "maintenance prefetch" intentionally redirect the destination
> > part away from refs/remotes/origin/ to avoid disrupting the
> > reference to @{upstream} etc. that are used locally.  And
> > intentionally doing so is good.
> > 
> > But imagine you are tracking my 'todo' branch which has nothing
> > common with the history of Git.  You'd have
> > 
> >     [remote "origin"]
> > 	url = git://git.kernel.org/pub/scm/git/git.git
> > 	fetch = +refs/heads/todo:refs/remotes/origin/todo
> > 
> > If "maintenance prefetch" does "+refs/heads/*:refs/prefetch/origin/*",
> > you'd end up the history of Git, which is not interesting for you who
> > are only interested in the 'todo' branch (to be checked out in the
> > Meta subdirectory to use Meta/cook script or read Meta/whats-cooking.txt
> > file).
> > 
> > So, redirecting the right-hand of configured refspec is a good idea;
> > not copying the left-hand of configured refspec, and unconditionally
> > using "refs/heads/*" is not.
>  
> This makes sense as a way to augment the feature. It doesn't seem
> like a common scenario, but it would be good for users to have
> that flexibility.

It's common for me, especially on repos requiring 'maintenance'.

> 
> Upon initial inspection, it shouldn't be too much work. However,
> there is some generality to the refspec that might not be wholly
> appropriate for prefetch (such as the exact_sha1 option). I'm
> unfamiliar with the advanced forms of the refspec, so it'll take
> some time to have confidence in this approach.

Didn't know about exact_sha1.  prefetch probably wouldn't do
anything in that case?

'negative' refspecs - hmm haven't tried those.  I see how that might
complicate things or maybe not.

generally isn't it still changing the right-hand side of refspec?

replacing ":refs/" with ":refs/prefetch/"

This would still work for refspecs with negative patterns right?

I'm willing to help with/test/review this, thanks for investigating.


> 
> Thanks,
> -Stolee