Re: Don't Call commit-msg Hooks With Empty Commit Messages

From: Junio C Hamano <gitster@pobox.com>
Date: Sep 17, 2021, 09:42 UTC
Message-ID: <xmqqlf3vilnb.fsf@gitster.g>
In-Reply-To: <CAO-Ogzs7vCtfgjZqp+cg1ERiu3bSwZM47arHJyyTrEqAQ=ZLcw@mail.gmail.com>

Kurt von Laven <kurt.von.laven@gmail.com> writes:

Show 15 quoted lines

> The most common reason commit messages are left empty is to abort
> them. commit-msg hooks that replace empty commit messages with
> non-empty ones (i) make it impossible to abort commits, (ii) are
> startling to developers joining a project configured in this manner,
> and (iii) can offer no value that wouldn't be equally or better
> offered another way. For instance, a default commit message would be
> better implemented as a commit message template or prepare-commit-msg
> hook. I propose that Git eventually cease calling commit-msg hooks
> when the commit-message is empty, but I would understand if backwards
> compatibility were the overriding concern. On the other hand, the
> empty commit message case is easy to overlook when crafting a
> commit-msg hook. One consequence of this behavior is that running the
> popular pre-commit tool (https://pre-commit.com/) tends to lead to a
> spew of false positives to the console on an aborted commit when
> configured with commit-msg hooks.

The primary reason commit-msg hook is there is *not* because we need a way to tweak the log message. As you said, prepare-commit-msg and templates are much better way to give some sort of default.

The purpose of the hook is to serve as the gatekeeper to cause an attempt with a bad commit message to fail. And a properly written commit-msg hook would be rejecting an empty message, instead of inserting cruft into an empty message file.

So, from that point of view, if we were to change anything, a more useful thing to do might be to forbid commit-msg hook from modifying the file and make sure it would only verify but not modify, I suspect. Doing so would have a side effect of making sure that no commit-msg hook will turn an empty message file into a non-empty message file ;-).