REST API: Ensure empty meta is returned as an object in view context

Author: liaisontw

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

@@ -58,8 +58,15 @@ public function filter_response_by_context( $data, $context ) {
 		unset( $data['content']['rendered'] );
 
 		// Add the core wp_pattern_sync_status meta as top level property to the response.
-		$data['wp_pattern_sync_status'] = $data['meta']['wp_pattern_sync_status'] ?? '';
-		unset( $data['meta']['wp_pattern_sync_status'] );
+		$meta                           = (array) $data['meta'];
+		$data['wp_pattern_sync_status'] = $meta['wp_pattern_sync_status'] ?? '';
+
+		if ( is_object( $data['meta'] ) ) {
+			unset( $data['meta']->wp_pattern_sync_status );
+		} else {
+			unset( $data['meta']['wp_pattern_sync_status'] );
+		}
+
 		return $data;
 	}
 

src/wp-includes/rest-api/fields/class-wp-rest-meta-fields.php

@@ -74,7 +74,8 @@ public function register_field() {
 	 *
 	 * @param int             $object_id Object ID to fetch meta for.
 	 * @param WP_REST_Request $request   Full details about the request.
-	 * @return array Array containing the meta values keyed by name.
+	 * @return array|object Array containing the meta values keyed by name,
+	 *                      or an empty object if to ensure JSON object encoding.
 	 */
 	public function get_value( $object_id, $request ) {
 		$fields   = $this->get_registered_fields();
@@ -105,6 +106,11 @@ public function get_value( $object_id, $request ) {
 			$response[ $name ] = $value;
 		}
 
+		// Use stdClass so that JSON result is {} and not [].
+		if ( empty( $response ) ) {
+			return (object) array();
+		}
+
 		return $response;
 	}
 
@@ -582,6 +588,10 @@ public static function prepare_value( $value, $request, $args ) {
 	 * @return array|false The meta array, if valid, false otherwise.
 	 */
 	public function check_meta_is_array( $value, $request, $param ) {
+		if ( is_object( $value ) ) {
+			$value = (array) $value;
+		}
+
 		if ( ! is_array( $value ) ) {
 			return false;
 		}

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

@@ -255,4 +255,39 @@ public function test_wp_patterns_sync_status_post_meta() {
 		$this->assertArrayHasKey( 'wp_pattern_sync_status', $data );
 		$this->assertArrayNotHasKey( 'wp_pattern_sync_status', $data['meta'] );
 	}
+
+	/**
+	 * Tests that check_meta_is_array correctly handles object types.
+	 *
+	 * @ticket 54484
+	 */
+	public function test_check_meta_is_array_accepts_object() {
+		wp_set_current_user( self::$user_ids['editor'] );
+
+		// Implement all abstract methods required by WP_REST_Meta_Fields.
+		$meta_fields = new class( 'post' ) extends WP_REST_Meta_Fields {
+			protected function get_meta_type() {
+				return 'post';
+			}
+
+			protected function get_rest_field_type() {
+				return 'post';
+			}
+		};
+
+		// Simulate an object parsed from JSON (stdClass).
+		$object_value           = new stdClass();
+		$object_value->test_key = 'test_value';
+
+		// Execute the method from the patch.
+		$result = $meta_fields->check_meta_is_array( $object_value, new WP_REST_Request(), 'meta' );
+
+		// Verify: The object should be converted to an array to pass validation.
+		$this->assertIsArray( $result, 'The object should be converted to an array to pass validation.' );
+		$this->assertArrayHasKey( 'test_key', $result );
+		$this->assertSame( 'test_value', $result['test_key'] );
+
+		// Verify: Values that are neither object nor array (e.g., string) should still return false.
+		$this->assertFalse( $meta_fields->check_meta_is_array( 'not-an-array', new WP_REST_Request(), 'meta' ) );
+	}
 }

tests/phpunit/tests/rest-api/rest-post-meta-fields.php

@@ -4014,4 +4014,60 @@ public static function data_scalar_default_values() {
 			'string default'  => array( 'string', 'string', 'string2' ),
 		);
 	}
+
+	/**
+	 * Tests that the Meta fields handle an empty object (stdClass) correctly.
+	 *
+	 * This verifies the compatibility of filter_response_by_context with object types
+	 * when meta is cast to an object (e.g., in specific PHP versions or filter modifications).
+	 *
+	 * @ticket 54484
+	 */
+	public function test_filter_response_by_context_with_empty_object_meta() {
+		wp_set_current_user( self::factory()->user->create( array( 'role' => 'editor' ) ) );
+
+		register_post_meta(
+			'post',
+			'test_object_compat_meta',
+			array(
+				'single'       => true,
+				'type'         => 'string',
+				'show_in_rest' => true,
+			)
+		);
+
+		add_filter(
+			'rest_prepare_post',
+			function ( $response ) {
+				$data = $response->get_data();
+				// Inject an empty object for meta to test type compatibility
+				$data['meta'] = new stdClass();
+				$response->set_data( $data );
+				return $response;
+			},
+			10
+		);
+
+		$request  = new WP_REST_Request( 'GET', '/wp/v2/posts/' . self::$post_id );
+		$response = rest_get_server()->dispatch( $request );
+		$data     = $response->get_data();
+
+		$this->assertArrayHasKey( 'meta', $data );
+
+		// Use a more robust check for both array and object types
+		$meta_data = $data['meta'];
+
+		if ( is_object( $meta_data ) ) {
+			$this->assertFalse(
+				property_exists( $meta_data, 'test_object_compat_meta' ),
+				'Failed asserting that the meta object does not have the property "test_object_compat_meta".'
+			);
+		} else {
+			$this->assertArrayNotHasKey(
+				'test_object_compat_meta',
+				$meta_data,
+				'Failed asserting that the meta array does not have the key "test_object_compat_meta".'
+			);
+		}
+	}
 }