git-send-email: Add References: headers to emails, in addition to In-Reply-To:

Signed-off-by: Ryan Anderson <rda@google.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/git-send-email.perl b/git-send-email.perl
index 312a4ea..ad8944d 100755 (executable)
--- a/git-send-email.perl
+++ b/git-send-email.perl
@@ -303,7 +303,7 @@ EOT
 }
 
 # Variables we set as part of the loop over files
-our ($message_id, $cc, %mail, $subject, $reply_to, $message);
+our ($message_id, $cc, %mail, $subject, $reply_to, $references, $message);
 
 sub extract_valid_address {
        my $address = shift;
@@ -367,7 +367,11 @@ Date: $date
 Message-Id: $message_id
 X-Mailer: git-send-email $gitversion
 ";
-       $header .= "In-Reply-To: $reply_to\n" if $reply_to;
+       if ($reply_to) {
+
+               $header .= "In-Reply-To: $reply_to\n";
+               $header .= "References: $references\n";
+       }
 
        if ($smtp_server =~ m#^/#) {
                my $pid = open my $sm, '|-';
@@ -482,6 +486,11 @@ foreach my $t (@files) {
        # set up for the next message
        if ($chain_reply_to || length($reply_to) == 0) {
                $reply_to = $message_id;
+               if (length $references > 0) {
+                       $references .= " $message_id";
+               } else {
+                       $references = "$message_id";
+               }
        }
        make_message_id();
 }