Re: Fetch-hooks

From: Leo Gaspard <leo@gaspard.io>
Date: Feb 10, 2018, 01:33 UTC
Message-ID: <9ab95c53-61e5-06a3-535e-a8916b3e5ec1@gaspard.io>
In-Reply-To: <xmqqvaf5tzw6.fsf@gitster-ct.c.googlers.com>

On 02/10/2018 02:08 AM, Junio C Hamano wrote:

Show 25 quoted lines

> Leo Gaspard <leo@gaspard.io> writes:
> 
>> On 02/10/2018 01:13 AM, Jeff King wrote:
>>> On Sat, Feb 10, 2018 at 12:49:31AM +0100, Leo Gaspard wrote:
>>>> So the changes that are required are:
>>>>  * Adding a notification-only post-fetch hook
> 
> Maybe I missed a very early part of the discussion, but why does
> this even need a hook?  There are some numbers [*1*] of classes of
> valid reasons we may want to have hooks triggered by operations, but
> "always do something locally after doing something else locally,
> regardless of the outcome of that something else" feels like the
> most typical anti-pattern that we do not want a hook for.  If you
> are doing "git fetch" (or "git pull"), you already know you are
> doing that and you donot need a notification.  You just create a
> workflow specific script that calls fetch or pull, followed by
> whatever you want to do and use that, instead of doing "git pull",
> and that is not any extra work than writing a hook and installing
> it.
> 
> Unlike something like post-receive, which happens on the remote side
> where you may not even have an interactive access to, in response to
> the operation you locally do (i.e. "git push"), fetching and then
> doing something else in a repository you fetch into has no reason to
> be done as a hook.

I guess the very early part of the discussion you're speaking of is what
I was assuming after reading
    https://marc.info/?l=git&m=132478296309094&w=2

Then, it's always possible to just write workflow-specific scripts that manually run git fetch then copy the refs (resp. run git fetch then copy the refs then run git merge) to get git myfetch (resp. git mypull) [1].

But then, the question is, why is there a pre-push hook? it's already possible to have a custom script that first runs the hook then runs git push, for most if not all of the use cases of the pre-push hook. Yet the possibility to not change the end-user's workflow is what makes pre-push (or pre-commit, with which the similarity is perhaps even more obvious) so useful.

So the reason for a post-fetch in my opinion is the same as for a pre-push / pre-commit: not changing the user's workflow, while providing additional features.

[1]

Which makes me notice that actually the post-fetch hook technique we were discussing with Peff suffers the same not-updating-FETCH_HEAD issue that was discussed in this early thread: a `git pull` would try to merge from refs/quarantine, I guess. So things are a bit harder than we thought.

I guess the tweak-fetch hook could be left “as-is”, but with git automatically doing the “quarantine-ing” thing transparently so that the references that the end-user (or the hook for that matter) see are the “curated” ones? Then it's too late for me to think efficiently right now, so that idea may be stupid or over-complex.