From: Phillip Wood <phillip.wood123@gmail.com>
Date: Sat, 14 Feb 2026 14:36:39 GMT
Subject: Re: [PATCH v2 2/2] templates: detect commit messages containing diffs
Message-ID: <20ed1f26-f60b-4e30-a0a5-8bd01dee19d1@gmail.com>
In-Reply-To: <xmqqfr74msm9.fsf@gitster.g>

On 13/02/2026 17:59, Junio C Hamano wrote:
> Phillip Wood <phillip.wood123@gmail.com> writes:
> 
>> From: Phillip Wood <phillip.wood@dunelm.org.uk>
>>
>> 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".

Thanks (I was confused for a minute because it says "format patch" above 
not "format match" but you're pointing out that it should be hypenated)

>> 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?

They do, but if the comment string is '$' then these two

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

have different meanings

Thanks

Phillip