Subject: Re: [PATCH] send-email: don't duplicate Reply-to:

From: Junio C Hamano <[email-masked]>
Date: Mon, 15 Sep 2025 18:14:28 -0700

Thanks for sending a patch.  

NeilBrown <[email-masked]> writes:

> If I run
>   git send-email --compose --reply-to 'ME <[email-masked]>' .....
>
> and edit the intro message, then the message will get two copies of the
> Reply-To field.  gmail.com rejects such messages.

A commit log message that begins with such a clearly written problem
description is always welcome.

> This happens because a Reply-To is inserted into the intro message
> template, and then the intro message headers are copied and another
> Reply-to is added.

OK.

It took me a few minutes to follow the code based on the above three
lines to figure out exactly what is going on.  The key realization I
needed was that the if/elsif/... chain being touched is sifting the
e-mail headers that appear in the message being sent into two kinds,
ones whose values are understood and parsed into individual variables
that have their own meaning (like $reply_to), and others that are
not understood by the code and thrown into @xh array to be blindly
replayed into the resulting message later.

By parsing the "Reply-To:" header into $reply_to, the code with your
patch stops throwing it in @xh and that is how duplicate headers are
prevented.

> This patch fixes the problem by noticing the Reply-To: header when the
> intro is parsed, and using it to assign $reply_to rather than blindly
> coping it into the new headers.

And what I thought missing is mentioned as part of the solution
here.  I would have preferred to see some more described in the
second paragraph that analyses how the breakage happens---it would
have saved me a few minutes ;-).

A few issues in the log message.

 * The commit, when prosessed by "git am", will record your name as
   "NeilBrown <[email-masked]>" because that is the name and
   address used on the "From:" header of the e-mail I am responding
   to.  It does not match the name/address used for sign-off below,
   which is not right.  If <[email-masked]> is the address you want
   to be known as to this project, you'd need to override the author
   name by inserting a line "From: NeilBrown <[email-masked]>" at
   the very beginning of the e-mail body, plus a blank line to
   separate it from the body of the message.

 * We prefer to see the solution described as if you are giving an
   order to somebody sitting on the keyboard to "make the code look
   like so", e.g.

     Fix the problem by parsing Reply-To: header into $reply_to
     variable, to be reproduced on a single header line later,
     instead of getting passed unrecognised and left in @xh to be
     copied into the outgoing message.

   or something like that.

> Signed-off-by: NeilBrown <[email-masked]>
> ---
>  git-send-email.perl | 3 +++
>  1 file changed, 3 insertions(+)

Thanks.

>
> diff --git a/git-send-email.perl b/git-send-email.perl
> index 437f8ac46a85..e2248c223119 100755
> --- a/git-send-email.perl
> +++ b/git-send-email.perl
> @@ -1931,6 +1931,9 @@ sub pre_process_file {
>  					$in_reply_to = $1;
>  				}
>  			}
> +			elsif (/^Reply-To: (.*)/i) {
> +				$reply_to = $1;
> +			}
>  			elsif (/^References: (.*)/i) {
>  				if (!$initial_in_reply_to || $thread) {
>  					$references = $1;