Interactivity API: Support length property on strings and arrays on the server

The Interactivity API tries to align client and server rendering so that the behavior is the same. Adds missing handling for `.length` to directives processing on the server on strings and numeric arrays which is inherently supported through JavaScript language on the client.

Props jonsurrell, gziolo, luisherranz.
Fixes #62582.


Built from https://develop.svn.wordpress.org/trunk@59477


git-svn-id: https://core.svn.wordpress.org/trunk@58863 1a063a9b-81f0-0310-95a4-ce76da25c4cd

Author: gziolo

wp-includes/interactivity-api/class-wp-interactivity-api.php

@@ -579,6 +579,36 @@ private function evaluate( $directive_value ) {
 		$path_segments = explode( '.', $path );
 		$current       = $store;
 		foreach ( $path_segments as $path_segment ) {
+			/*
+			 * Special case for numeric arrays and strings. Add length
+			 * property mimicking JavaScript behavior.
+			 *
+			 * @since 6.8.0
+			 */
+			if ( 'length' === $path_segment ) {
+				if ( is_array( $current ) && array_is_list( $current ) ) {
+					$current = count( $current );
+					break;
+				}
+
+				if ( is_string( $current ) ) {
+					/*
+					 * Differences in encoding between PHP strings and
+					 * JavaScript mean that it's complicated to calculate
+					 * the string length JavaScript would see from PHP.
+					 * `strlen` is a reasonable approximation.
+					 *
+					 * Users that desire a more precise length likely have
+					 * more precise needs than "bytelength" and should
+					 * implement their own length calculation in derived
+					 * state taking into account encoding and their desired
+					 * output (codepoints, graphemes, bytes, etc.).
+					 */
+					$current = strlen( $current );
+					break;
+				}
+			}
+
 			if ( ( is_array( $current ) || $current instanceof ArrayAccess ) && isset( $current[ $path_segment ] ) ) {
 				$current = $current[ $path_segment ];
 			} elseif ( is_object( $current ) && isset( $current->$path_segment ) ) {

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.8-alpha-59476';
+$wp_version = '6.8-alpha-59477';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.