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

From: Junio C Hamano <[email-masked]>
Date: Fri, 17 Sep 2021 02:42:00 -0700

Kurt von Laven <[email-masked]> writes:

> 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 ;-).