Re: [RFC/PATCH 0/2] place cherry pick line below commit title

From: Jonathan Tan <jonathantanmy@google.com>
Date: Sep 30, 2016, 18:22 UTC
Message-ID: <11e41a94-df8c-494a-584b-e2bc8da2de3a@google.com>
In-Reply-To: <xmqqtwcycqul.fsf@gitster.mtv.corp.google.com>

On 09/29/2016 02:56 PM, Junio C Hamano wrote:

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> Jonathan Tan <jonathantanmy@google.com> writes:
>
>> This is somewhat of a follow-up to my previous e-mail with subject
>> "[PATCH] sequencer: support folding in rfc2822 footer" [1], in which I
>> proposed relaxing the definition of a commit message footer to allow
>> multiple-line field bodies (as described in RFC2822), but its strictness
>> was deemed deliberate.
>
> It does not necessarily mean we can never change it when we did
> something deliberately, though.  With a good enough justification,
> and with a transitition plan if the backward incompatibility is
> severe enough to warrant one, we can change things.
>
> I vaguely recall that there were some discussion on the definition
> of "what's a trailer line" with folks from the kernel land, perhaps
> while discussing the interpret-trailers topic.  IIRC, when somebody
> passes an improved version along, the resulting message's trailer
> block may look like this:
>
>     Signed-off-by: Original Author <original@author.xz>
>     [fixed typo in the variable names]
>     Signed-off-by: Somebhody Else <somebody@else.xz>
>
> and an obvious "wish" of theirs was to treat not just RFC2822-like
> "a line that begins with token followed by a colon" but also these
> short comments as part of the trailer block.  Your original wish in
> [*1*] is to also treat "a line that begin with a whitespace that
> follows a line that begins with token followed by a colon" as part
> of the trailer block and I personally think that is a reasonable
> thing to wish for, too.

If we allowed arbitrary lines in the trailer block, this would solve my original problem, yes.

> I recall that I was somewhat surprised and dissapointed to see no
> change to interpret-trailers when you tried [*1*], which was really
> about improving the definition of what the trailer block is, by the
> way.

Sorry, I had missed that.

Looking at that, it seems that sequencer.c started interpreting the last paragraph of the commit message as a footer and adding an exception for "cherry picked from" in commit b971e04 ("sequencer.c: always separate "(cherry picked from" from commit body", 2013-02-12). So the interpretations of sequencer.c and interpret-trailers were already divergent, but I should have probably at least discussed that.

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>> Below is a patch set that allows placing the "cherry picked from" line
>> without taking into account the definition of a commit message footer.
>> For example, "git cherry-pick -x" (with the appropriate configuration
>> variable or argument) would, to this commit message:
>>
>>   commit title
>>
>>   This is an explanatory paragraph.
>>
>>   Footer: foo
>>
>> place the "(cherry picked from ...)" line below "commit title".
>>
>> Would this be better?
>
> It is not immediately obvious what such a change buys us.  Wouldn't
> the current code place that line below "Footer: foo"?  I cannot
> think of any reason why anybody would want to place "cherry-picked
> from" immediately below the title and before the first line of the
> body.

Yes, the current code would place it below "Footer: foo" without a blank line before it, but if it thinks that the so-called footer is not actually a footer, it would insert a blank line before that line.

As for a reason:

1) I do not have a specific reason for placing it in that exact 
position, but I would like to be able to place the "cherry picked from" 
line without affecting the last paragraph (specifically, without making 
the "cherry picked from" line the only line in the last paragraph). It 
seems to me that placing it below the title was the most straightforward 
way to do that - this way, Git can have its own idea of what a footer 
constitutes, and the user can treat it as completely separate from the 
"cherry picked from" line mechanism.

1a) (Avoiding the footer might also be a good way of more clearly defining what the footer is. For example, currently, "cherry picked from" is treated as a special case in sequencer.c but not in trailer.c, as far as I can tell. If we consistently avoided the footer, we wouldn't need such a special case anywhere.)

2) The Linux kernel's repository has some "commit ... upstream." lines 
in this position (below the commit title) - for example, in commit 
dacc0987fd2e.

[1] https://kernel.googlesource.com/pub/scm/linux/kernel/git/stable/linux-stable/+/dacc0987fd2e25a8b4b8c19778862ba12ce76d0a