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From: Junio C Hamano <gitster@pobox.com>
To: Maxime Louet <maxime@saumon.io>
Cc: git@vger.kernel.org
Subject: Re: Verbose commit message diff not showing changes from pre-commit hook
Date: Sat, 25 Jul 2020 08:31:01 -0700	[thread overview]
Message-ID: <xmqqk0yripca.fsf@gitster.c.googlers.com> (raw)
In-Reply-To: <xmqqr1sziqrm.fsf@gitster.c.googlers.com> (Junio C. Hamano's message of "Sat, 25 Jul 2020 08:00:13 -0700")

Junio C Hamano <gitster@pobox.com> writes:

> Maxime Louet <maxime@saumon.io> writes:
>
>> Is this expected behaviour? I find it somehow confusing that the diff
>> in the commit message isn't the actual commit diff.
>
> Since the designed purpose of pre-commit hook is to examine the
> contents to be committed and reject the attempt to commit if there
> is something wrong found, and Git does not expect it to munge the
> contents to be committed, if the hook does so, you would get an
> undefined behaviour.  So anything is totally expected at that point.

Sorry, I have to take this back.

Even before ec84bd00 (git-commit: Refactor creation of log message.,
2008-02-05), the code anticipated that pre-commit may touch the index
and tried to cope with it.

However, ec84bd00 moved the place where we re-read the on-disk index
in the sequence, and updated a message that used to read:

-	/*
-	 * Re-read the index as pre-commit hook could have updated it,
-	 * and write it out as a tree.
-	 */

to:

+	/*
+	 * Re-read the index as pre-commit hook could have updated it,
+	 * and write it out as a tree.  We must do this before we invoke
+	 * the editor and after we invoke run_status above.
+	 */

Unfortunately there is no mention of the reason why we "must" here.
I think the "run_status above" is what prepared the patch in the log
message template, so it is quite likely that we deliberately did so
to exclude whatever munging pre-commit does to the index from
appearing in the patch in the verbose mode.  If I have to guess, I
think the reason is because pre-commit automation is expected to be
some sort of mechanical change and not part of the actual work that
the end-user produced, it would become easier to perform the "final
review" of "what have I done so far---does everything make sense?"
if such "extra" changes are excluded.

So, in short, it is not "undefined", but rather it seems to be a
designed behaviour that we are seeing.

Thanks.

  reply	other threads:[~2020-07-25 15:31 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-25 14:47 Verbose commit message diff not showing changes from pre-commit hook Maxime Louet
2020-07-25 15:00 ` Junio C Hamano
2020-07-25 15:31   ` Junio C Hamano [this message]
2020-07-26 17:41     ` René Scharfe
2020-07-26 19:45       ` Maxime Louet
2020-07-27 18:13       ` Paolo Bonzini

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