On Fri, Feb 06, 2026 at 10:48:29AM +0100, Florian Weimer wrote:

quoted

On Fri, Feb 06, 2026 at 09:59:31AM +0100, Florian Weimer wrote:

quoted

Isn't the format-patch output already unambiguous because the sequence
of diffs is preceeded by the non-diff statistics section, and only then
the commit message follows?  It's just not possible to process this
correctly in one pass because only at the end of the input, you know
that you have just seen the to-be-applied diffs.

That diffstat is optional, and not parsed by the receiving format-patch
at all. Keep in mind that in the world for which it was originally
designed, people were not necessarily using Git to generate their
emails. They could be patches emailed by random folks using "diff"
themselves.

Is the git am format that flexible in practice?  I often have trouble
applying patches with git am that were created with git format-patch
and have to resort to plain old patch instead.  As a user, I definitely
get the impression that it's not a type of tool that gets a patch
out of an email message, no matter what the cost.

I'm sure there are corner cases it doesn't handle, but it will take
input like this:

git am <<\EOF
From: Jeff King <redacted>
Date: Fri Feb 6 03:42:12 2026 -0500
Subject: my cool patch

this fixes some stuff

diff -Nru old/file new/file

--- old/file	2026-02-06 04:58:56.148348259 -0500
+++ new/file	2026-02-06 04:58:59.432360938 -0500

@@ -1 +1 @@
-base
+changed

EOF


and happily produce the commit you'd expect. I generated the diff there
with GNU diff, and typed the rest. Likewise for this version with
attachments, which I generated with mutt:

git am <<\EOF
Date: Fri, 6 Feb 2026 05:03:31 -0500
From: Jeff King <redacted>
To: Jeff King <redacted>
Subject: my cool patch
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="tveeCB9LAhLXuhMJ"
Content-Disposition: inline


--tveeCB9LAhLXuhMJ
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline

see the attached patch, which does blah blah blah

--tveeCB9LAhLXuhMJ
Content-Type: text/plain; charset=utf-8
Content-Disposition: attachment; filename=patch

diff -Nru old/file new/file

--- old/file	2026-02-06 04:58:56.148348259 -0500
+++ new/file	2026-02-06 04:58:59.432360938 -0500

@@ -1 +1 @@
-base
+changed

--tveeCB9LAhLXuhMJ--

EOF


I expect that Linus saw a lot of this kind of stuff in the early days.
I'd guess it's pretty rare now, but I won't be surprised if there are
some die-hards generating kernel patches with who-knows-what. ;)

-Peff