Re: [PATCH v2 2/2] templates: detect commit messages containing diffs

Phillip Wood [off-list ref] writes:

From: Phillip Wood <redacted>

If the body of a commit message contains a diff that is not indented
then "git am" will treat that diff as part of the patch rather than
as part of the commit message. This allows it to apply email messages
that were created by adding a commit message in front of a regular diff
without adding the "---" separator used by "git format-patch". This
often surprises users [1-4] so add a check to the sample "commit-msg"
hook to reject messages that would confuse "git am". Even if a project
does not use an email based workflow it is not uncommon for people
to generate patches from it and apply them with "git am". Therefore
it is still worth discouraging the creation of commit messages that
would not be applied correctly.

A further source of confusion when applying patches with "git am" is
the "---" separator that is added by "git format patch". If a commit
message body contains that line then it will be truncated by "git am".
As this is often used by patch authors to add some commentary that
they do not want to end up in the commit message when the patch is
applied, the hook does not complain about the presence of "---" lines
in the message.

"git format match" -> "git format-patch".

Detecting if the message contains a diff is complicated by the
hook being passed the message before it is cleaned up so we need to
ignore any diffs below the scissors line.

Sorry, but I do not quite understand the logic here.  In e-mailed
messages, the way the scissors line is most commonly used is to have
something like this.

	Hi, I read your problem report, and I think what is going on
	is ... (lengthy discussion here).

	Can you try this patch?

	--- >8 ---
	Subject: frotz: try working around nitfol

	As we cannot easily tell if the gostak will distim these
	patciular doshes, let's be careful to see ...

	diff - will be used to confuse the mailinfo

	Signed-off-by: a.u.thour
	---
	(diffstat here)
	(patch here)

and "diff - will be used to confuse" is something we would want to
notice.  But I am not sure if the use case of committing a scissors
line.  You help those who write a three-dash line and materials
meant to be kept outside of the final commit at the end, so if is
this an attempt to help those who write a scissors line and
materials meant to be kept outside of the final commit at the
beginning, I can understand, but then don't you want to notice "diff
-" that appears after the scissors line?  I do not offhand remember
what happens to a "diff -" that appears before the scissors (i.e.,
if you write "diff -" before "Can you try this patch?"), but I
wouldn't be surprised if mailinfo stopped there long before it sees
the scissors.

There are also two possible
config keys to check to find the comment character at the start of
the scissors line.

Also I do not think scissors requires to be a comment.

So, I am a bit confused.

The first paragraph of the commit message becomes
the email subject header which beings "Subject: " and so does not
need to be checked.

Great.

The trailing ".*" when matching commented lines
ensures that if the comment string ends with a "$" it is not treated
as an anchor.

I am not sure what this means.  Wouldn't these three

	sed -e '/^#/d'
	sed -e '/^#.*/d'
	sed -e '/^#.*$/d'

work exactly the same way?

Thanks.