REST API: Make sure the class_list property is a list

Author: dlh01

src/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php

@@ -2101,7 +2101,7 @@ public function prepare_item_for_response( $item, $request ) {
 			}
 
 			if ( rest_is_field_included( 'class_list', $fields ) ) {
-				$data['class_list'] = get_post_class( array(), $post->ID );
+				$data['class_list'] = array_values( get_post_class( array(), $post->ID ) );
 			}
 		}
 

tests/phpunit/tests/rest-api/rest-posts-controller.php

@@ -2775,6 +2775,35 @@ public function test_prepare_item_override_excerpt_length() {
 		);
 	}
 
+	/**
+	 * Test that the `class_list` property is a list.
+	 *
+	 * @ticket 64247
+	 *
+	 * @covers WP_REST_Posts_Controller::prepare_item_for_response
+	 */
+	public function test_class_list_is_list() {
+		$post_id = self::factory()->post->create();
+
+		// Filter 'post_class' to add a duplicate, which should be removed by `array_unique()`, causing a non-indexed array.
+		add_filter(
+			'post_class',
+			function ( $classes ) {
+				return array_merge(
+					array( 'duplicate-class', 'duplicate-class' ),
+					$classes,
+				);
+			}
+		);
+
+		$request = new WP_REST_Request( 'GET', '/wp/v2/posts/' . $post_id );
+		$response = rest_do_request( $request );
+		$data = $response->get_data();
+
+		$this->assertTrue( isset( $data['class_list'] ) );
+		$this->assertTrue( array_is_list( $data['class_list'] ) );
+	}
+
 	public function test_create_item() {
 		wp_set_current_user( self::$editor_id );