[PATCH 2/4] format-patch: fix a bug in option exclusivity and add a test to t4014

[Dragan Simic <dsimic@manjaro.org>]

Fix a bug that allows --rfc and -k options to be specified together when
executing "git format-patch".  This bug was introduced back in the commit
e0d7db7423a9 ("format-patch: --rfc honors what --subject-prefix sets"),
about eight months ago, but it has remained undetected so far, presumably
because of no associated test coverage.

Add a new test to the t4014 that covers the mutual exclusivity of the --rfc
and -k command-line options for "git format-patch", for future coverage.

Signed-off-by: Dragan Simic <dsimic@manjaro.org>
---
 builtin/log.c           | 5 ++++-
 t/t4014-format-patch.sh | 4 ++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/builtin/log.c b/builtin/log.c
index c0a8bb95e983..e5a238f1cf2c 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -2050,8 +2050,11 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 	if (cover_from_description_arg)
 		cover_from_description_mode = parse_cover_from_description(cover_from_description_arg);
 
-	if (rfc)
+	/* Also mark the subject prefix as modified, for later checks */
+	if (rfc) {
 		strbuf_insertstr(&sprefix, 0, "RFC ");
+		subject_prefix = 1;
+	}
 
 	if (reroll_count) {
 		strbuf_addf(&sprefix, " v%s", reroll_count);
diff --git a/t/t4014-format-patch.sh b/t/t4014-format-patch.sh
index e37a1411ee24..e22c4ac34e6e 100755
--- a/t/t4014-format-patch.sh
+++ b/t/t4014-format-patch.sh
@@ -1397,6 +1397,10 @@ test_expect_success '--rfc is argument order independent' '
 	test_cmp expect actual
 '
 
+test_expect_success '--rfc and -k cannot be used together' '
+	test_must_fail git format-patch -1 --stdout --rfc -k >patch
+'
+
 test_expect_success '--from=ident notices bogus ident' '
 	test_must_fail git format-patch -1 --stdout --from=foo >patch
 '