Re: [BUG] send-email propagates "In-Reply-To"

[Jeff King <peff@peff.net>]

On Sun, Aug 22, 2021 at 09:24:12AM +0000, Marvin Häuser wrote:

> "git send-email" propagates the "In-Reply-To" header of the last prior patch
> with such defined to subsequent patches which do not define such explicitly.
> I suspect this behaviour is incorrect as I could not find any documentation
> on this. I'm sorry if this behaviour is actually expected, and would be
> happy if someone could point me to the appropriate documentation. This was
> reproduced on Fedora 34 with git 2.33.0 and "--no-thread".
> 
> Steps to reproduce:
> 1. Create two patches, one of which has an "In-Reply-To" field
> ("patch-in-reply.patch") and one of which does not
> ("patch-no-in-reply.patch").
> 2. Run "git send-email --dry-run --no-thread patch-in-reply.patch
> patch-no-in-reply.patch"
> 2.1. Observe the emission of an "In-Reply-To" header for
> "patch-no-in-reply.patch" with no such header.
> 3. Run "git send-email --dry-run --no-thread patch-no-in-reply.patch
> patch-in-reply.patch"
> 3.1. Observe the omission of an "In-Reply-To" header for
> "patch-no-in-reply.patch" with no such header.
> 
> Expected behaviour:
> With no threading and no other sorts of explicitly defining the
> "In-Reply-To" header, I expect to always observe the behaviour of 3.1., and
> to not observe the behaviour of 2.1.

Yes, I think this is just a bug. If the user requested --no-thread, then
we should be sending each patch as it appears on disk, with no
modification to the in-reply-to header.

> The "issue" is "in_reply_to" is overwritten here [1], which is the main loop
> worker to process all files passed to send-email [2], but it is not restored
> for subsequent patches. Unless required otherwise (e.g. send-email
> threading), it should be restored to its default value for each patch I
> believe.

Right. Most of the values we parse are declared inside the process_file
function, and so start empty. $in_reply_to is special in that we need to
carry its value across multiple files, so we need to always handle it in
each loop iteration, whether we are setting it to a new value or
resetting it to null.

> I wrote a quick patch to adjust 2.1. to 3.1. [3]. I have no time right now
> to review the submission guidelines (and thus did not submit the patch
> "properly" yet), but I will try to get to that tonight or some time next
> week. If in the mean time you could provide any feedback on the behaviour or
> the patch, so that I can get things right the first time, that would be
> great!

Your patch looks like the right direction. Handling $references at the
same time is the right thing to do. The extra setting of $subject seems
weird, though.

We'd want to add a test to t/t9001-send-email.sh, too, I'd think.

-Peff