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

From: Junio C Hamano <gitster@pobox.com>
Date: Apr 1, 2021, 20:14 UTC
Message-ID: <xmqq8s613gqa.fsf@gitster.g>
In-Reply-To: <d246df21-fdaa-a391-847a-e03e8e664af1@gmail.com>

Derrick Stolee <stolee@gmail.com> writes:

Show 10 quoted lines

> 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.

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.