Re: [PATCH 0/3] commit-msg.sample: reject messages that would confuse "git am"

From: Jeff King <peff@peff.net>
Date: Feb 9, 2026, 06:57 UTC
Message-ID: <20260209065703.GA585828@coredump.intra.peff.net>
In-Reply-To: <cover.1770476279.git.phillip.wood@dunelm.org.uk>

On Sat, Feb 07, 2026 at 02:57:59PM +0000, Phillip Wood wrote:

Show 14 quoted lines

> From: Phillip Wood <phillip.wood@dunelm.org.uk>
> 
> On 06/02/2026 09:03, Jeff King wrote:
> > I don't think there is a way to unambiguously parse the single-stream
> > output that format-patch produces. This is a reasonably well-known
> > gotcha (at least around here). E.g., some earlier discussions:
> >
> >    2024:https://lore.kernel.org/git/ca13705ae4817ffba16f97530637411b59c9eb19.camel@scientia.org/
> >    2022:https://lore.kernel.org/git/d0b577825124ac684ab304d3a1395f3d2d0708e8.1662333027.git.matheus.bernardino@usp.br/
> >    2015:https://lore.kernel.org/git/CAFOYHZC6Qd9wkoWPcTJDxAs9u=FGpHQTkjE-guhwkya0DRVA6g@mail.gmail.com/
> 
> If we cannot improve "git am" perhaps we should update our sample
> "commit-msg" hook to reject messages that will cause problems. Here
> are some patches to do that.

I'm not entirely opposed to it, but my initial reaction was two bits of skepticism:

  1. I imagine that hardly anybody runs commit-msg hooks in the first
     place, let alone our sample hook. So I doubt this will get the
     attention of many people.

  2. I'd guess that these days only a small minority of people care
     about sending patches by email. So for most people, a warning about
     their commit message containing a diff or "---" will be mostly
     useless, if not outright confusing.

I'd imagine that documentation updates would be more likely to get read by users than the sample hook. And a warning in git-commit itself would be even more obvious (but fall even more afoul of (2) above). Adding a warning to format-patch would help with (2), but at that point it may be too late to change the commit message.

Show 7 quoted lines

> We could perhaps think about adding a more prominent warning to the
> "git am" and "git format-patch" documentation. The docs for "git am"
> mention that it splits the message on a line starting with "diff -"
> but maybe we should spell out what that means for commit messages that
> include a diff. In principle "git format-patch" could also warn or
> error out if it creates a mail that "git am" cannot import verbatim,
> I don't know how hard that would be in implement.

I think the patch from Matheus linked above added that format-patch check.

-Peff