Re: [PATCH v4] hooks: propose project configured hooks

[Jonathan Tan <jonathantanmy@google.com>]

> > From the implementation point of view, would it be sufficient to just
> > advertise that hooks are available? Assuming that the hooks will be
> > available from a specially named ref (as stated below), then we would
> > only need to inform the user that this ref exists and hooks can be
> > inspected using a special command. Likewise for when we fetch and notice
> > that the ref now points to a different object. Then, we wouldn't need to
> > do any extra fetching upon clone/fetch, saving time and bandwidth, but
> > just do so if the user requests it.
> >
> 
> From a user perspective, I think it's better to not just tell users
> that hooks are available but also /what/ hooks are available.
> 
> That said, that doesn't require getting everything from the ref as the
> hook command itself might be stored in this ref. So something like
> this seems sufficient to me: "Origin suggests setting up a `pre-push`
> hook which runs `pre_push.sh`. To view the contents of `pre_push.sh`,
> run {special command}."

I agree that on its own, more information upfront is better than less.
But we can't store anything more than an object ID (a SHA-1 hash) in a
ref, though. Knowing anything beyond the object ID would require
fetching some objects, which incurs time and bandwidth (perhaps
comparatively a tiny amount in well-behaved repos, but we still need to
acknowledge that). (Well, there is also the possibility of using
multiple refs to communicate which hooks are present and which are not,
but I think that's too cumbersome.)

> > Right now hooks are fixed files (well, not counting Emily Shaffer's work
> > on config hooks). Would it be sufficient to just provide replacements
> > for those files?
> >
> 
> My thought was we'd leverage config hooks and basically write to the
> config for setting up hooks.

The config hooks work is still in progress, so I think we need to
support both the legacy way and the new way. I think this shouldn't be a
problem since both ways involve writing something somewhere.

In any case, if the aim is to support config hooks, I think it's clearer
if this section just says "write a config" without explaining what the
config can do, since that is the responsibility of the config hooks
feature. (But then there remains the question of whether there will be a
whitelist of acceptable configs to write.)

> > Hmm...what would be a use case of this? And how would, say, a pre-commit
> > hook know which remote it is for?
> >
> 
> For a concrete example, we use Gerrit for internal reviews and need
> the Change-Id hook, but we don't want that when upstreaming.
> 
> Good question for specifying remotes. This might imply the need for
> something like `git commit --hooks-from=origin`.

I think passing a parameter to choose which hook to invoke is beyond the
scope of upstream-supplied hooks. (Also, I don't think that this
situation is resolved by having 2 remotes providing 2 different sets of
hooks. Perhaps one of the remote's set knows to set the Change-Id
trailer, but the other set would not know that it needs to remove a
specific trailer.)

> > This seems contradictory to a point above where we only inform the user
> > upon clone (when the user is in the setup mood).
> >
> 
> Good catch, I should clarify that previous point. The main concern is
> prompting before a hook will execute which would get in the way of
> existing workflows, making users susceptible to blindly agreeing.
> Showing advice after the fact doesn't get in the way, and this is one
> reason why "advice" felt like the right terminology to use (more
> below): it's merely a helpful message that a user can optionally
> choose to follow.

Ah, I see. I'm still not sure that it is a good idea. Firstly, the user
should have already made this decision when they read the message at
clone time, and secondly, this advice might come too late (a pre-commit
hook might be "salvageable" but a push hook might not). Having said
that, the presence or absence of this doesn't affect the overall design
and implementation, so we can leave this in if you want.

> > > +* If, after fetch, the central repository suggests new or updated hooks, the
> > > +user should receive advice to install these new hooks (note: implementation
> > > +should not interfere with requirement listed in "Fast Follows")
> >
> > In Git, the term "advice" seems to be used more for extra
> > explanations that you can turn off once you're experienced with Git.
> > Here, these seem like things that we would want to notify users about
> > regardless of experience level, so maybe the word "notification" is more
> > appropriate.
> >
> 
> Another reason to use "advice" here is because the existing system
> allows users to turn off the advice when it's not needed for the
> requirement: "The user should be able to use configuration to turn off
> this advice."
> 
> Do advice settings work on a per-clone basis? If not, I agree "advice"
> is probably not the right term.

Those settings don't work per-clone. My main point, though, is that the
user probably would always need to know if there are new hooks.

> No, that's what I meant by "Fast Follows" -- not needed for the initial feature.

Ah, maybe call it "future work" then. "Fast follows" is not a term I'm
familiar with (and searching online, it doesn't seem like a common term
either).