Merge branch 'rj/add-p-typo-reaction' into next

When the user responds to a prompt given by "git add -p" with an
unsupported command, list of available commands were given, which
was too much if the user knew what they wanted to type but merely
made a typo.  Now the user gets a much shorter error message.

* rj/add-p-typo-reaction:
  add-patch: response to unknown command

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);
 		}
 	}
 

t/t3701-add-interactive.sh

@@ -7,6 +7,8 @@ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-terminal.sh
 
+SP=" "
+
 diff_cmp () {
 	for x
 	do
@@ -55,6 +57,19 @@ 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 &&
@@ -231,7 +246,6 @@ test_expect_success 'setup file' '
 '
 
 test_expect_success 'setup patch' '
-	SP=" " &&
 	NULL="" &&
 	cat >patch <<-EOF
 	@@ -1,4 +1,4 @@