[PATCH v4 2/3] rebase: stop accepting --rebase-merges=""

[Alex Henrie <alexhenrie24@gmail.com>]

The unusual syntax --rebase-merges="" (that is, --rebase-merges with an
empty string argument) has been an undocumented synonym of
--rebase-merges=no-rebase-cousins. Stop accepting that syntax to avoid
confusion when a rebase.merges config option is introduced, where
rebase.merges="" will be equivalent to not passing --rebase-merges.

Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>
---
 builtin/rebase.c         | 6 ++----
 t/t3430-rebase-merges.sh | 6 ++++++
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 6635f10d52..b68fc2fbb7 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -1140,7 +1140,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		{OPTION_STRING, 'r', "rebase-merges", &rebase_merges,
 			N_("mode"),
 			N_("try to rebase merges instead of skipping them"),
-			PARSE_OPT_OPTARG, NULL, (intptr_t)""},
+			PARSE_OPT_OPTARG, NULL, (intptr_t)"no-rebase-cousins"},
 		OPT_BOOL(0, "fork-point", &options.fork_point,
 			 N_("use 'merge-base --fork-point' to refine upstream")),
 		OPT_STRING('s', "strategy", &options.strategy,
@@ -1437,9 +1437,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		imply_merge(&options, "--exec");
 
 	if (rebase_merges) {
-		if (!*rebase_merges)
-			; /* default mode; do nothing */
-		else if (!strcmp("rebase-cousins", rebase_merges))
+		if (!strcmp("rebase-cousins", rebase_merges))
 			options.rebase_cousins = 1;
 		else if (strcmp("no-rebase-cousins", rebase_merges))
 			die(_("Unknown mode: %s"), rebase_merges);
diff --git a/t/t3430-rebase-merges.sh b/t/t3430-rebase-merges.sh
index d46d9545f2..c73949df18 100755
--- a/t/t3430-rebase-merges.sh
+++ b/t/t3430-rebase-merges.sh
@@ -278,6 +278,12 @@ test_expect_success 'do not rebase cousins unless asked for' '
 	EOF
 '
 
+test_expect_success '--rebase-merges="" is invalid syntax' '
+	echo "fatal: Unknown mode: " >expect &&
+	test_must_fail git rebase --rebase-merges="" HEAD^ 2>actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'refs/rewritten/* is worktree-local' '
 	git worktree add wt &&
 	cat >wt/script-from-scratch <<-\EOF &&
-- 
2.39.2