sequencer: fix gpg option passed to merge subcommand

When performing a rebase with --rebase-merges using either a custom
strategy specified with -s or an octopus merge, and at the same time
having gpgsign enabled (either rebase -S or config commit.gpgsign), the
operation would fail on making the merge commit. Instead of "-S%s" with
the key id substituted, only the bare key id would get passed to the
underlying merge command, which tried to interpret it as a ref.

Fix the issue and add test cases as suggested by Johannes Schindelin and
Junio C Hamano.

Signed-off-by: Samuel Čavoj <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: sammko

sequencer.c

@@ -3677,7 +3677,7 @@ static int do_merge(struct repository *r,
 		strvec_push(&cmd.args, "-F");
 		strvec_push(&cmd.args, git_path_merge_msg(r));
 		if (opts->gpg_sign)
-			strvec_push(&cmd.args, opts->gpg_sign);
+			strvec_pushf(&cmd.args, "-S%s", opts->gpg_sign);
 
 		/* Add the tips to be merged */
 		for (j = to_merge; j; j = j->next)

t/t3435-rebase-gpg-sign.sh

@@ -68,4 +68,25 @@ test_expect_failure 'rebase -p --no-gpg-sign override commit.gpgsign' '
 	test_must_fail git verify-commit HEAD
 '
 
+test_expect_success 'rebase -r, merge strategy, --gpg-sign will sign commit' '
+	git reset --hard merged &&
+	test_unconfig commit.gpgsign &&
+	git rebase -fr --gpg-sign -s resolve --root &&
+	git verify-commit HEAD
+'
+
+test_expect_success 'rebase -r, merge strategy, commit.gpgsign=true will sign commit' '
+	git reset --hard merged &&
+	git config commit.gpgsign true &&
+	git rebase -fr -s resolve --root &&
+	git verify-commit HEAD
+'
+
+test_expect_success 'rebase -r, merge strategy, commit.gpgsign=false --gpg-sign will sign commit' '
+	git reset --hard merged &&
+	git config commit.gpgsign false &&
+	git rebase -fr --gpg-sign -s resolve --root &&
+	git verify-commit HEAD
+'
+
 test_done