Add initial PHP rendering code

lib/blocks.php

@@ -79,6 +79,7 @@ function gutenberg_reregister_core_block_types() {
 				'page-list.php'                    => 'core/page-list',
 				'page-list-item.php'               => 'core/page-list-item',
 				'pattern.php'                      => 'core/pattern',
+				'pattern-template.php'             => 'core/pattern-template',
 				'post-author.php'                  => 'core/post-author',
 				'post-author-name.php'             => 'core/post-author-name',
 				'post-author-biography.php'        => 'core/post-author-biography',

packages/block-library/src/pattern-template/index.php

@@ -0,0 +1,90 @@
+<?php
+/**
+ * Server-side rendering of the `core/pattern` block.
+ *
+ * @package WordPress
+ */
+
+/**
+ *  Registers the `core/pattern` block on the server.
+ *
+ * @return void
+ */
+function register_block_core_pattern_template() {
+	register_block_type_from_metadata(
+		__DIR__ . '/pattern-template',
+		array(
+			'render_callback' => 'render_block_core_pattern_template',
+		)
+	);
+}
+
+/**
+ * Replaces token blocks with the matching placeholder block.
+ *
+ * @param WP_Block_List $content_blocks     The content inner blocks.
+ * @param array         $placeholder_blocks The block's content.
+ *
+ * @return WP_Block_List The compiled block list.
+ */
+function block_core_pattern_template_replace_content_tokens_with_placeholder_blocks( $content_block, $placeholder_blocks ) {
+	$content_blocks              = $content_block->inner_blocks;
+	static $placeholder_position = 0;
+
+	// If there are no blocks, there's nothing to do.
+	if ( 0 === count( $content_blocks ) ) {
+		return $content_blocks;
+	}
+
+	foreach ( $content_blocks as $index => $inner_block ) {
+		// Recurse and update any inner blocks of this block first.
+		if ( count( $inner_block->inner_blocks ) ) {
+			block_core_pattern_template_replace_content_tokens_with_placeholder_blocks( $inner_block, $placeholder_blocks );
+		}
+
+		// If this is a token, replace it with the placeholder that's in this position.
+		if ( 'core/pattern-template-token' === $inner_block->name ) {
+			if ( isset( $placeholder_blocks[ $placeholder_position ] ) ) {
+				// TODO - it might be better to create a new inner blocks list instead of overwriting the existing one.
+				$content_blocks[ $index ] = $placeholder_blocks[ $placeholder_position ];
+				$placeholder_position     = $placeholder_position + 1;
+			}
+		}
+	}
+}
+
+/**
+ * Renders the `core/pattern` block on the server.
+ *
+ * @param array $attributes Block attributes.
+ * @param array $content    The block's content.
+ * @param array $block      The WP_Block object.
+ *
+ * @return string Returns the output of the pattern template.
+ */
+function render_block_core_pattern_template( $attributes, $content, $block ) {
+	$inner_blocks = $block->inner_blocks;
+
+	$content_block       = null;
+	$placeholders_blocks = array();
+
+	foreach ( $inner_blocks as $inner_block ) {
+		if ( 'core/pattern-template-content' === $inner_block->name ) {
+			$content_block = $inner_block;
+		} else {
+			array_push( $placeholders_blocks, $inner_block );
+		}
+	}
+
+	block_core_pattern_template_replace_content_tokens_with_placeholder_blocks( $content_block, $placeholders_blocks );
+
+	$compiled_content = '';
+
+	foreach ( $content_block->inner_blocks as $inner_block ) {
+		$compiled_content .= $inner_block->render();
+	}
+
+	return $compiled_content;
+}
+
+add_action( 'init', 'register_block_core_pattern_template' );