[PATCH v5 2/2] add-patch: response to unknown command

["Rubén Justo" <rjusto@gmail.com>]

When the user gives an unknown command to the "add -p" prompt, the list
of accepted commands with their explanation is given.  This is the same
output they get when they say '?'.

However, the unknown command may be due to a user input error rather
than the user not knowing the valid command.

To reduce the likelihood of user confusion and error repetition, instead
of displaying the list of accepted commands, display a short error
message with the unknown command received, as feedback to the user.

Include a reminder about the current command '?' in the new message, to
guide the user if they want help.

Signed-off-by: Rubén Justo <rjusto@gmail.com>
---
 add-patch.c                |  5 ++++-
 t/t3701-add-interactive.sh | 16 +++++++++++++++-
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/add-patch.c b/add-patch.c
index fc0eed4fd4..2252895c28 100644
--- a/add-patch.c
+++ b/add-patch.c
@@ -1667,7 +1667,7 @@ static int patch_update_file(struct add_p_state *s,
 			}
 		} else if (s->answer.buf[0] == 'p') {
 			rendered_hunk_index = -1;
-		} else {
+		} else if (s->answer.buf[0] == '?') {
 			const char *p = _(help_patch_remainder), *eol = p;
 
 			color_fprintf(stdout, s->s.help_color, "%s",
@@ -1691,6 +1691,9 @@ static int patch_update_file(struct add_p_state *s,
 				color_fprintf_ln(stdout, s->s.help_color,
 						 "%.*s", (int)(eol - p), p);
 			}
+		} else {
+			err(s, _("Unknown command '%s' (use '?' for help)"),
+			    s->answer.buf);
 		}
 	}
 
diff --git a/t/t3701-add-interactive.sh b/t/t3701-add-interactive.sh
index c5531520cb..28a95a775d 100755
--- a/t/t3701-add-interactive.sh
+++ b/t/t3701-add-interactive.sh
@@ -8,6 +8,8 @@ TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-terminal.sh
 
+SP=" "
+
 diff_cmp () {
 	for x
 	do
@@ -56,6 +58,19 @@ test_expect_success 'warn about add.interactive.useBuiltin' '
 	done
 '
 
+test_expect_success 'unknown command' '
+	test_when_finished "git reset --hard; rm -f command" &&
+	echo W >command &&
+	git add -N command &&
+	git diff command >expect &&
+	cat >>expect <<-EOF &&
+	(1/1) Stage addition [y,n,q,a,d,e,p,?]? Unknown command ${SQ}W${SQ} (use ${SQ}?${SQ} for help)
+	(1/1) Stage addition [y,n,q,a,d,e,p,?]?$SP
+	EOF
+	git add -p -- command <command >actual 2>&1 &&
+	test_cmp expect actual
+'
+
 test_expect_success 'setup (initial)' '
 	echo content >file &&
 	git add file &&
@@ -232,7 +247,6 @@ test_expect_success 'setup file' '
 '
 
 test_expect_success 'setup patch' '
-	SP=" " &&
 	NULL="" &&
 	cat >patch <<-EOF
 	@@ -1,4 +1,4 @@
-- 
2.45.0.2.g84ce137e4a