[RFC PATCH] send-email: allow fixing the cover letter subject

["Carlo Marcelo Arenas Belón" <carenas@gmail.com>]

a03bc5b6ad (send-email: Refuse to send cover-letter template
subject, 2009-06-08) fixes a common problem with the direct use
of `git send-email` to send topics, where the cover letter will
be a template by accident.

Allow using --subject to fix the --cover-letter subject and skip
the safety check without having to use --force.

Note that the use of --compose is also allowed, and will also
get its Subject set through the commandline, but it might make
more sense to instead make them incompatible and force editing
the cover letter instead, hence why sending this only as a RFC.

patch is based on another one[1] still in fly, and the documentation
change is long overdue, but probably should need a better
explanation; lastly using a non ASCII subject also needs fixing,
but it also affects compose, so was left out for now.

Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>

[1] https://lore.kernel.org/git/4db7759c-2123-533b-9f89-954c07f5832a@posteo.de/
---
 Documentation/git-send-email.txt |  3 +--
 git-send-email.perl              |  8 ++++++--
 t/t9001-send-email.sh            | 16 +++++++++++++++-
 3 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/Documentation/git-send-email.txt b/Documentation/git-send-email.txt
index 3db4eab4ba..9d2bfa6095 100644
--- a/Documentation/git-send-email.txt
+++ b/Documentation/git-send-email.txt
@@ -113,8 +113,7 @@ is not set, this will be prompted for.
 
 --subject=<string>::
 	Specify the initial subject of the email thread.
-	Only necessary if --compose is also set.  If --compose
-	is not set, this will be prompted for.
+	Only necessary if --compose or --cover-letter are also set.
 
 --to=<address>,...::
 	Specify the primary recipient of the emails generated. Generally, this
diff --git a/git-send-email.perl b/git-send-email.perl
index fd79849530..a33328a5d9 100755
--- a/git-send-email.perl
+++ b/git-send-email.perl
@@ -997,7 +997,7 @@ sub file_declares_8bit_cte {
 				  default => "UTF-8");
 }
 
-if (!$force) {
+if (!$force and not defined $initial_subject) {
 	for my $f (@files) {
 		if (get_patch_subject($f) =~ /\Q*** SUBJECT HERE ***\E/) {
 			die sprintf(__("Refusing to send because the patch\n\t%s\n"
@@ -1719,7 +1719,6 @@ sub process_file {
 	@xh = ();
 	my $input_format = undef;
 	my @header = ();
-	$subject = $initial_subject;
 	$message = "";
 	$message_num++;
 	# First unfold multiline header fields
@@ -1747,6 +1746,11 @@ sub process_file {
 		if (defined $input_format && $input_format eq 'mbox') {
 			if (/^Subject:\s+(.*)$/i) {
 				$subject = $1;
+
+				if (defined $initial_subject &&
+				$subject =~ /\Q*** SUBJECT HERE ***\E/) {
+					$subject = $initial_subject;
+				}
 			}
 			elsif (/^From:\s+(.*)$/i) {
 				($author, $author_encoding) = unquote_rfc2047($1);
diff --git a/t/t9001-send-email.sh b/t/t9001-send-email.sh
index 747872d5be..043532fe85 100755
--- a/t/t9001-send-email.sh
+++ b/t/t9001-send-email.sh
@@ -1728,7 +1728,6 @@ test_expect_success $PREREQ 'CRLF and sendemail.transferencoding=base64' '
 	test_cmp expected actual
 '
 
-
 # Note that the patches in this test are deliberately out of order; we
 # want to make sure it works even if the cover-letter is not in the
 # first mail.
@@ -1765,6 +1764,21 @@ test_expect_success $PREREQ '--force sends cover letter template anyway' '
 	test -n "$(ls msgtxt*)"
 '
 
+test_expect_success $PREREQ '--subject can be used to fix the cover letter' '
+	clean_fake_sendmail &&
+	git send-email \
+		--cover-letter -2 \
+		--subject="foo" \
+		--from="Example <nobody@example.com>" \
+		--to=nobody@example.com \
+		--smtp-server="$(pwd)/fake.sendmail" \
+		2>errors >out &&
+	! grep "SUBJECT HERE" errors &&
+	ls msgtxt* >list &&
+	test_line_count = 3 list &&
+	grep "Subject: foo" msgtxt1
+'
+
 test_cover_addresses () {
 	header="$1"
 	shift
-- 
2.33.0.481.g26d3bed244