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

[Derrick Stolee <stolee@gmail.com>]

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.

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.

Thanks,
-Stolee