Blocks: Fix layout support to be compatible with enhanced pagination.

Make layout support compatible with enhanced pagination by ensuring that generated class names are stable across pagination, even when the number of rendered posts is different.

With the previous implementation of enhanced pagination, the CSS corresponding to each block was not detected. Therefore, for enhanced pagination to work correctly, the CSS of the blocks present in the Post Template must be stable on all pages.

The number of posts rendered by the Query block is always the same, except in the last page, where it can be only a fraction. If any of the blocks rendered by the Post Template used the `wp_unique_id` function, the ID (which is incremental) would have been different than in the previous pages and the class names would have varied.

This is remediated by this changeset by replacing the usage of `wp_unique_id` in the layout support (which is used by the Query block) with an implementation that uses IDs that are incremental only for that block. That way, the generated class names are never affected by the number of times `wp_unique_id` runs.

Props luisherranz, andrewserong, isabel_brison, costdev, mukesh27, cbravobernal, hellofromTonya, jorbin.
Merges [56994] to the 6.4 branch.
Fixes #59681.
Built from https://develop.svn.wordpress.org/branches/6.4@56995


git-svn-id: http://core.svn.wordpress.org/branches/6.4@56506 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/block-supports/layout.php

@@ -630,7 +630,16 @@ function wp_render_layout_support_flag( $block_content, $block ) {
 
 	$class_names        = array();
 	$layout_definitions = wp_get_layout_definitions();
-	$container_class    = wp_unique_id( 'wp-container-' );
+
+	/*
+	 * Uses an incremental ID that is independent per prefix to make sure that
+	 * rendering different numbers of blocks doesn't affect the IDs of other
+	 * blocks. Makes the CSS class names stable across paginations
+	 * for features like the enhanced pagination of the Query block.
+	 */
+	$container_class = wp_unique_prefixed_id(
+		'wp-container-' . sanitize_title( $block['blockName'] ) . '-layout-'
+	);
 
 	// Set the correct layout type for blocks using legacy content width.
 	if ( isset( $used_layout['inherit'] ) && $used_layout['inherit'] || isset( $used_layout['contentSize'] ) && $used_layout['contentSize'] ) {

wp-includes/functions.php

@@ -7830,6 +7830,40 @@ function wp_unique_id( $prefix = '' ) {
 	return $prefix . (string) ++$id_counter;
 }
 
+/**
+ * Generates an incremental ID that is independent per each different prefix.
+ *
+ * It is similar to `wp_unique_id`, but each prefix has its own internal ID
+ * counter to make each prefix independent from each other. The ID starts at 1
+ * and increments on each call. The returned value is not universally unique,
+ * but it is unique across the life of the PHP process and it's stable per
+ * prefix.
+ *
+ * @since 6.4.0
+ *
+ * @param string $prefix Optional. Prefix for the returned ID. Default empty string.
+ * @return string Incremental ID per prefix.
+ */
+function wp_unique_prefixed_id( $prefix = '' ) {
+	static $id_counters = array();
+
+	if ( ! is_string( $prefix ) ) {
+		wp_trigger_error(
+			__FUNCTION__,
+			sprintf( 'The prefix must be a string. "%s" data type given.', gettype( $prefix ) )
+		);
+		$prefix = '';
+	}
+
+	if ( ! isset( $id_counters[ $prefix ] ) ) {
+		$id_counters[ $prefix ] = 0;
+	}
+
+	$id = ++$id_counters[ $prefix ];
+
+	return $prefix . (string) $id;
+}
+
 /**
  * Gets last changed date for the specified cache group.
  *

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.4-RC1-56993';
+$wp_version = '6.4-RC1-56995';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.