Re: bug report: cover letter is inheriting last patch's message ID with send-email

>
> Junio C Hamano <gitster@pobox.com> writes:
>
> >> # With the attached patches, where all of the patches have a
> >> # Message-Id but the cover letter doesn't.
> >> git send-email *.patch
>
> I suspect this is a recent regression with the addition of the
> pre_process_file step.  56adddaa (send-email: refactor header
> generation functions, 2023-04-19) makes all messages parsed
> before the first message is sent out, by calling a sub
> "pre_process_file" before invoking the validate hook.  The same sub
> is called again for each message when it is sent out, as the
> processing in that step is shared between the time the message gets
> vetted and the time the message gets sent.
>
> Unfortunately, $message_id variable is assigned to in that sub.  So
> it is very much understandable why this happens.
>
> I wonder if it is just doing something silly like this?
>
> --- >8 ---
> Subject: [PATCH] send-email: clear the $message_id after validation
>
> Recently git-send-email started parsing the same message twice, once
> to validate _all_ the message before sending even the first one, and
> then after the validation hook is happy and each message gets sent,
> to read the contents to find out where to send to etc.
>
> Unfortunately, the effect of reading the messages for validation
> lingered even after the validation is done.  Namely $message_id gets
> assigned if exists in the input files but the variable is global,
> and it is not cleared before pre_process_file runs.  This causes
> reading a message without a message-id followed by reading a message
> with a message-id to misbehave---the sub reports as if the message
> had the same id as the previously written one.
>
> Clear the variable before starting to read the headers in
> pre_process_file
>
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
>
>  * I am not surprised at all if there are similar problems in this
>    function around variables other than $message_id; this patch is
>    merely reacting to the bug report and not systematically hunting
>    and fixing the bugs coming from the same root cause.  If the
>    original author of the pre_process_file change is still around,
>    the second sets of eyes from them is very much appreciated.
>
>  git-send-email.perl | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git c/git-send-email.perl w/git-send-email.perl
> index 89d8237e89..889ef388c8 100755
> --- c/git-send-email.perl
> +++ w/git-send-email.perl
> @@ -1771,6 +1771,7 @@ sub send_message {
>  sub pre_process_file {
>         my ($t, $quiet) = @_;
>
> +       undef $message_id;
>         open my $fh, "<", $t or die sprintf(__("can't open file %s"), $t);
>
>         my $author = undef;