Rewrite Rules: Fix rewrite rules breaking for taxonomies with URL-encoded Unicode slugs

src/wp-includes/class-wp-rewrite.php

@@ -1844,7 +1844,13 @@ public function add_permastruct( $name, $struct, $args = array() ) {
 			$struct = $this->root . $struct;
 		}
 
-		$args['struct'] = $struct;
+		$args['struct'] = preg_replace_callback(
+			'/(?:%[0-9A-F]{2})+/',
+			static function ( $matches ) {
+				return rawurldecode( $matches[0] );
+			},
+			$struct
+		);
 
 		$this->extra_permastructs[ $name ] = $args;
 	}

tests/phpunit/tests/rewrite/permastructs.php

@@ -14,6 +14,13 @@ public function set_up() {
 		$this->set_permalink_structure( '/%postname%/' );
 	}
 
+	public function tear_down() {
+		remove_permastruct( 'wptests_cert' );
+		unregister_taxonomy( 'wptests_cert' );
+
+		parent::tear_down();
+	}
+
 	public function test_add_permastruct() {
 		global $wp_rewrite;
 
@@ -31,6 +38,7 @@ public function test_add_permastruct() {
 			),
 			$wp_rewrite->extra_permastructs['foo']
 		);
+		remove_permastruct( 'foo' );
 	}
 
 	public function test_remove_permastruct() {
@@ -43,4 +51,34 @@ public function test_remove_permastruct() {
 		remove_permastruct( 'foo' );
 		$this->assertArrayNotHasKey( 'foo', $wp_rewrite->extra_permastructs );
 	}
+
+	/**
+	 * Tests that a URL-encoded Unicode taxonomy slug is decoded in the permastruct and
+	 * that the generated rewrite rules correctly map the taxonomy query var to $matches[1].
+	 *
+	 * @ticket 41791
+	 */
+	public function test_add_permastruct_with_url_encoded_unicode_slug() {
+		global $wp_rewrite;
+
+		register_taxonomy(
+			'wptests_cert',
+			'post',
+			array(
+				'rewrite' => array(
+					'slug' => urlencode( 'Сертификат' ),
+				),
+			)
+		);
+
+		$stored_struct = $wp_rewrite->extra_permastructs['wptests_cert']['struct'];
+
+		// The struct must store decoded Unicode, not percent-encoded sequences.
+		$this->assertStringContainsString( 'Сертификат', $stored_struct );
+		$this->assertStringNotContainsString( urlencode( 'Сертификат' ), $stored_struct );
+
+		// The generated rules must map the taxonomy var to $matches[1], not a shifted index.
+		$rules = $wp_rewrite->generate_rewrite_rules( $stored_struct );
+		$this->assertContains( 'index.php?wptests_cert=$matches[1]', array_values( $rules ) );
+	}
 }