Don't accept empty option group names for dropdown elements

When this code parses a string that looks like this:

*
** A
** B

It creates an option group with 2 options, but the name
of the group is an empty string. This makes the OOUI
DropdownInputWidget fail later.

Since the empty group name is useless anyway, drop it. This
makes the code behave as if the parsed string looked like
this:

* A
* B

Live example for the issue:
https://el.wikipedia.org/wiki/MediaWiki:Protect-dropdown

Bug: T275125
Change-Id: I780c1be27740b0ed3b35aa569b5a528112d7238f

2 files changed, 10 insertions, 5 deletions

diff --git a/includes/xml/Xml.php b/includes/xml/Xml.php
index 4462f1a55165..f07e35859444 100644
--- a/includes/xml/Xml.php
+++ b/includes/xml/Xml.php
@@ -557,10 +557,14 @@ class Xml {
 			} elseif ( substr( $value, 0, 1 ) == '*' && substr( $value, 1, 1 ) != '*' ) {
 				# A new group is starting...
 				$value = trim( substr( $value, 1 ) );
-				# Do not use the value for 'other' as option group - T251351
-				$optgroup = isset( $params['other'] ) && $params['other'] === $value
-					? false
-					: $value;
+				if ( $value !== '' &&
+					// Do not use the value for 'other' as option group - T251351
+					( !isset( $params['other'] ) || $value !== $params['other'] )
+				) {
+					$optgroup = $value;
+				} else {
+					$optgroup = false;
+				}
 			} elseif ( substr( $value, 0, 2 ) == '**' ) {
 				# groupmember
 				$opt = trim( substr( $value, 2 ) );
diff --git a/tests/phpunit/includes/XmlTest.php b/tests/phpunit/includes/XmlTest.php
index 8ff2afbecabb..3f0ee0121283 100644
--- a/tests/phpunit/includes/XmlTest.php
+++ b/tests/phpunit/includes/XmlTest.php
@@ -375,6 +375,7 @@ class XmlTest extends MediaWikiIntegrationTestCase {
 		$this->assertEquals(
 			[
 				'other reasons' => 'other',
+				'Empty group item' => 'Empty group item',
 				'Foo' => [
 					'Foo 1' => 'Foo 1',
 					'Example' => 'Example',
@@ -384,7 +385,7 @@ class XmlTest extends MediaWikiIntegrationTestCase {
 				],
 			],
 			Xml::listDropDownOptions(
-				"* Foo\n** Foo 1\n** Example\n* Bar\n** Bar 1",
+				"*\n** Empty group item\n* Foo\n** Foo 1\n** Example\n* Bar\n** Bar 1",
 				[ 'other' => 'other reasons' ]
 			)
 		);