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

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: do not show UI messages on stderr

add-patch.c

@@ -293,10 +293,9 @@ static void err(struct add_p_state *s, const char *fmt, ...)
 	va_list args;
 
 	va_start(args, fmt);
-	fputs(s->s.error_color, stderr);
+	fputs(s->s.error_color, stdout);
-	vfprintf(stderr, fmt, args);
+	vprintf(fmt, args);
-	fputs(s->s.reset_color, stderr);
+	puts(s->s.reset_color);
-	fputc('\n', stderr);
 	va_end(args);
 }
 
@@ -1326,7 +1325,7 @@ static int apply_for_checkout(struct add_p_state *s, struct strbuf *diff,
 		err(s, _("Nothing was applied.\n"));
 	} else
 		/* As a last resort, show the diff to the user */
-		fwrite(diff->buf, diff->len, 1, stderr);
+		fwrite(diff->buf, diff->len, 1, stdout);
 
 	return 0;
 }
@@ -1668,7 +1667,7 @@ soft_increment:
 			}
 		} 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",
@@ -1692,6 +1691,9 @@ soft_increment:
 				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);
 		}
 	}
 
@@ -1778,9 +1780,9 @@ int run_add_p(struct repository *r, enum add_p_mode mode,
 			break;
 
 	if (s.file_diff_nr == 0)
-		fprintf(stderr, _("No changes.\n"));
+		err(&s, _("No changes."));
 	else if (binary_count == s.file_diff_nr)
-		fprintf(stderr, _("Only binary files changed.\n"));
+		err(&s, _("Only binary files changed."));
 
 	add_p_state_clear(&s);
 	return 0;

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
@@ -45,17 +47,30 @@ test_expect_success 'warn about add.interactive.useBuiltin' '
 	cat >expect <<-\EOF &&
 	warning: the add.interactive.useBuiltin setting has been removed!
 	See its entry in '\''git help config'\'' for details.
-	No changes.
 	EOF
+	echo "No changes." >expect.out &&
 
 	for v in = =true =false
 	do
 		git -c "add.interactive.useBuiltin$v" add -p >out 2>actual &&
-		test_must_be_empty out &&
+		test_cmp expect.out out &&
 		test_cmp expect actual || return 1
 	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 @@
@@ -335,13 +349,13 @@ test_expect_success 'different prompts for mode change/deleted' '
 
 test_expect_success 'correct message when there is nothing to do' '
 	git reset --hard &&
-	git add -p 2>err &&
+	git add -p >out &&
-	test_grep "No changes" err &&
+	test_grep "No changes" out &&
 	printf "\\0123" >binary &&
 	git add binary &&
 	printf "\\0abc" >binary &&
-	git add -p 2>err &&
+	git add -p >out &&
-	test_grep "Only binary files changed" err
+	test_grep "Only binary files changed" out
 '
 
 test_expect_success 'setup again' '