Patterns: Don't inject theme attribute on frontend.

Having the patterns registry inject the `theme` attribute into all Template Part blocks inside every pattern was found to negatively impact performance. It turns out that it's only required for the editor (i.e. in the REST API) but not on the frontend; there, it's instead possible to fall back to the currently active theme.

The latter change was made to the Pattern and Template Part blocks in WordPress/gutenberg#55217, which was sync'ed to Core in [56849]. Consequently, this changeset removes `theme` attribute insertion from the frontend.

Props flixos90, gziolo, dmsnell, hellofromtonya.
Fixes #59583.
Built from https://develop.svn.wordpress.org/trunk@56896


git-svn-id: http://core.svn.wordpress.org/trunk@56407 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/block-template-utils.php

@@ -549,15 +549,18 @@ function _build_block_template_result_from_file( $template_file, $template_type
 		$template->area = $template_file['area'];
 	}
 
-	$before_block_visitor = '_inject_theme_attribute_in_template_part_block';
+	$before_block_visitor = ( defined( 'REST_REQUEST' ) && REST_REQUEST ) ? '_inject_theme_attribute_in_template_part_block' : null;
 	$after_block_visitor  = null;
 	$hooked_blocks        = get_hooked_blocks();
 	if ( ! empty( $hooked_blocks ) || has_filter( 'hooked_block_types' ) ) {
 		$before_block_visitor = make_before_block_visitor( $hooked_blocks, $template );
 		$after_block_visitor  = make_after_block_visitor( $hooked_blocks, $template );
 	}
-	$blocks            = parse_blocks( $template_content );
-	$template->content = traverse_and_serialize_blocks( $blocks, $before_block_visitor, $after_block_visitor );
+	if ( null !== $before_block_visitor || null !== $after_block_visitor ) {
+		$blocks           = parse_blocks( $template_content );
+		$template_content = traverse_and_serialize_blocks( $blocks, $before_block_visitor, $after_block_visitor );
+	}
+	$template->content = $template_content;
 
 	return $template;
 }

wp-includes/blocks.php

@@ -779,7 +779,9 @@ function make_before_block_visitor( $hooked_blocks, $context ) {
 	 * @return string The serialized markup for the given block, with the markup for any hooked blocks prepended to it.
 	 */
 	return function ( &$block, $parent_block = null, $prev = null ) use ( $hooked_blocks, $context ) {
-		_inject_theme_attribute_in_template_part_block( $block );
+		if ( defined( 'REST_REQUEST' ) && REST_REQUEST ) {
+			_inject_theme_attribute_in_template_part_block( $block );
+		}
 
 		$markup = '';
 

wp-includes/class-wp-block-patterns-registry.php

@@ -165,14 +165,16 @@ public function unregister( $pattern_name ) {
 	private function prepare_content( $pattern, $hooked_blocks ) {
 		$content = $pattern['content'];
 
-		$before_block_visitor = '_inject_theme_attribute_in_template_part_block';
+		$before_block_visitor = ( defined( 'REST_REQUEST' ) && REST_REQUEST ) ? '_inject_theme_attribute_in_template_part_block' : null;
 		$after_block_visitor  = null;
 		if ( ! empty( $hooked_blocks ) || has_filter( 'hooked_block_types' ) ) {
 			$before_block_visitor = make_before_block_visitor( $hooked_blocks, $pattern );
 			$after_block_visitor  = make_after_block_visitor( $hooked_blocks, $pattern );
 		}
-		$blocks  = parse_blocks( $content );
-		$content = traverse_and_serialize_blocks( $blocks, $before_block_visitor, $after_block_visitor );
+		if ( null !== $before_block_visitor || null !== $after_block_visitor ) {
+			$blocks  = parse_blocks( $content );
+			$content = traverse_and_serialize_blocks( $blocks, $before_block_visitor, $after_block_visitor );
+		}
 
 		return $content;
 	}

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.4-beta3-56849';
+$wp_version = '6.4-beta3-56896';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.