Blocks: Add new render property in block.json for block types

New `render` field in `block.json` file that accepts a string value. It allows to pass a path to the PHP file that is going to be used to render the block on the server.  Related PR in Gutenberg: WordPress/gutenberg#42430.

Props spacedmonkey, luisherranz, welcher, noisysocks, matveb, fabiankaegy, aristath, zieladam.
Fixes #53148.


Built from https://develop.svn.wordpress.org/trunk@54132

wp-includes/blocks.php

@@ -235,6 +235,7 @@ function get_block_metadata_i18n_schema() {
  * @since 5.5.0
  * @since 5.7.0 Added support for `textdomain` field and i18n handling for all translatable fields.
  * @since 5.9.0 Added support for `variations` and `viewScript` fields.
+ * @since 6.1.0 Added support for `render` field.
  *
  * @param string $file_or_folder Path to the JSON file with metadata definition for
  *                               the block or path to the folder where the `block.json` file is located.
@@ -345,6 +346,33 @@ function register_block_type_from_metadata( $file_or_folder, $args = array() ) {
 		);
 	}
 
+	if ( ! empty( $metadata['render'] ) ) {
+		$template_path = wp_normalize_path(
+			realpath(
+				dirname( $metadata['file'] ) . '/' .
+				remove_block_asset_path_prefix( $metadata['render'] )
+			)
+		);
+		if ( file_exists( $template_path ) ) {
+			/**
+			 * Renders the block on the server.
+			 *
+			 * @since 6.1.0
+			 *
+			 * @param array    $attributes Block attributes.
+			 * @param string   $content    Block default content.
+			 * @param WP_Block $block      Block instance.
+			 *
+			 * @return string Returns the block content.
+			 */
+			$settings['render_callback'] = function( $attributes, $content, $block ) use ( $template_path ) { // phpcs:ignore VariableAnalysis.CodeAnalysis.VariableAnalysis.UnusedVariable
+				ob_start();
+				require $template_path;
+				return ob_get_clean();
+			};
+		}
+	}
+
 	/**
 	 * Filters the settings determined from the block type metadata.
 	 *

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.1-alpha-54131';
+$wp_version = '6.1-alpha-54132';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.