Subject: Re: RFC: Supporting .git/hooks/$NAME.d/* && /etc/git/hooks/$NAME.d/*

From: Junio C Hamano <[email-masked]>
Date: Mon, 25 Apr 2016 10:45:45 -0700

Ævar Arnfjörð Bjarmason <[email-masked]> 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.

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.

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 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/.

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...