git@vger.kernel.org list mirror (unofficial, one of many)
 help / color / Atom feed
From: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: Git <git@vger.kernel.org>
Subject: Re: RFC: Supporting .git/hooks/$NAME.d/* && /etc/git/hooks/$NAME.d/*
Date: Tue, 26 Apr 2016 12:58:04 +0200
Message-ID: <CACBZZX6AYBYeb5S4nEBhYbx1r=icJ81JGYBx5=H4wacPhHjFbQ@mail.gmail.com> (raw)
In-Reply-To: <xmqq4mapmvjq.fsf@gitster.mtv.corp.google.com>

On Mon, Apr 25, 2016 at 7:45 PM, Junio C Hamano <gitster@pobox.com> wrote:
> Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:
>
>> The reason for supporting the *.d directories was that I spotted a lot
>> of hooks people had hacked up at work using the pee(1) command[1] to
>> run sequences of other unrelated hook commands.
>
> IIRC, we wanted to do this several years ago but after discussion
> decided that we didn't want to have this in the core, because we
> didn't want to hardcode the policy on interaction among multiple
> hooks.

Ah, would be interesting to see that discussion if someone knows
enough to dig it up, didn't find it with some brief searching.

> You can easily resolve the ordering of hooks--just declare that they
> are executed sequentially in strcmp() order of filenames and users
> will know to prefix them with fixed-number-of-digits to force their
> desired ordering without complaining.

In principle you're describing glob() order here:
http://pubs.opengroup.org/onlinepubs/7908799/xsh/glob.html

We don't set LC_COLLATE in git so this'll be C order, which I think
will just fall back to strcmp().

If it doesn't and there's a functional difference, I'm not sure, it's
probably less confusing to use glob() order, since that's what you'll
get with shell expansion.

I.e. it would be confusing if you expand the hooks in the shell, and
git executes them in a slightly different order.

> What is harder and the core part cannot unilaterally dictate is what
> should happen after seeing a failure/rejection from a hook.  Some
> hooks among the remainder would not want to be even called.  Some
> others do want to be called but want to learn that the previous
> hooks already have decided to fail/reject the operation.  There may
> even be some others that cannot be moved to earlier part of the hook
> chain for other external constraints (e.g. side effect of some
> previous hook is part of its input), but would want to override the
> previous decision to reject and let the operation pass.

I think it's fair enough to say that if we had this facility this
would be good enough:

 * Your hooks are executed in glob() order, local .git first, then /etc/git/...

 * If it's a hook like pre-commit that can reject something the first
hook to fail short-circuits. I.e. none of the rest get executed.

 * If it's not a hook like that e.g. post-commit all of the hooks will
get executed.

 * If you need anything more complex you can just wrap your hooks in
your own shellscript.

I.e. it takes care of the common case where:

 * You just want to execute N hooks and don't want to write a wrapper.

 * For pre-* hooks the common case is it doesn't matter /what/
rejected things, just that it gets rejected, e.g. for pre-receive.
Also if you care about performance you can order them in
cheapest-first order.

> I am happy to see that the idea brought back alive again, but I
> think we prefer this start its life clearly marked as "highly
> experimental and subject to change", then invite interested and
> brave users who tolerate backward incompatible changes to
> experiment, in order to allow us to gauge what the right semantics
> and flexibility the users would want.  One way to do so may be an
> opt-in configuration variable e.g. "experimental.multiHooks";
> another may be to implement the logic as a pair of scripts (one for
> the command line argument variant, the other for stdin variant) and
> ship them in contrib/.

Makes sense to have an experimental.* config tree for git for stuff like this.

> The latter approach (i.e. scripting) might be easier for people to
> experiment and tweak, and in the olden days that would certainly be
> the approach would would have taken, but I am not too afraid of
> appearing uninviting to casual scripters anymore these days, so...

Yeah, actually one thing I didn't think of is that the core.hooksPath
patch I submitted makes this rather trivial to implement as a
collection of scripts...

  reply index

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-04-22 23:51 Ævar Arnfjörð Bjarmason
2016-04-25 17:45 ` Junio C Hamano
2016-04-26 10:58   ` Ævar Arnfjörð Bjarmason [this message]
2016-04-26 13:40     ` Marc Branchaud
2016-04-26 16:09       ` Ævar Arnfjörð Bjarmason
2016-04-26 17:52         ` Christian Couder
2016-04-26 21:09         ` Marc Branchaud
2016-04-26 21:52     ` Junio C Hamano

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

  List information: http://vger.kernel.org/majordomo-info.html

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CACBZZX6AYBYeb5S4nEBhYbx1r=icJ81JGYBx5=H4wacPhHjFbQ@mail.gmail.com' \
    --to=avarab@gmail.com \
    --cc=git@vger.kernel.org \
    --cc=gitster@pobox.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

git@vger.kernel.org list mirror (unofficial, one of many)

Archives are clonable:
	git clone --mirror https://public-inbox.org/git
	git clone --mirror http://ou63pmih66umazou.onion/git
	git clone --mirror http://czquwvybam4bgbro.onion/git
	git clone --mirror http://hjrcffqmbrq6wope.onion/git

Example config snippet for mirrors

Newsgroups are available over NNTP:
	nntp://news.public-inbox.org/inbox.comp.version-control.git
	nntp://ou63pmih66umazou.onion/inbox.comp.version-control.git
	nntp://czquwvybam4bgbro.onion/inbox.comp.version-control.git
	nntp://hjrcffqmbrq6wope.onion/inbox.comp.version-control.git
	nntp://news.gmane.io/gmane.comp.version-control.git

 note: .onion URLs require Tor: https://www.torproject.org/

AGPL code for this site: git clone https://public-inbox.org/public-inbox.git