Add support for custom templates in FSE themes

lib/full-site-editing/page-templates.php

@@ -0,0 +1,42 @@
+<?php
+/**
+ * Support for page templates.
+ *
+ * @package gutenberg
+ */
+
+/**
+ * Load the page templates in Gutenberg.
+ *
+ * @param array    $templates Page templates.
+ * @param WP_Theme $theme     WP_Theme instance.
+ * @param WP_Post  $post      The post being edited, provided for context, or null.
+ * @return array (Maybe) modified page templates array.
+ */
+function gutenberg_load_block_page_templates( $templates, $theme, $post ) {
+	if ( ! gutenberg_is_fse_theme() ) {
+		return $templates;
+	}
+	$config_file = locate_template( 'experimental-theme.json' );
+	if ( ! file_exists( $config_file ) ) {
+		return $templates;
+	}
+	$data           = json_decode(
+		file_get_contents( $config_file ),
+		true
+	);
+	$page_templates = array();
+	if ( isset( $data['pageTemplates'] ) ) {
+		foreach ( $data['pageTemplates']  as $key => $page_template ) {
+			if ( ( ! isset( $page_template['postTypes'] ) && 'page' === $post->post_type ) ||
+				( isset( $page_template['postTypes'] ) && in_array( $post->post_type, $page_template['postTypes'], true ) )
+			) {
+				$page_templates[ $key ] = $page_template['title'];
+			}
+		}
+	}
+
+	return $page_templates;
+}
+add_filter( 'theme_post_templates', 'gutenberg_load_block_page_templates', 10, 3 );
+add_filter( 'theme_page_templates', 'gutenberg_load_block_page_templates', 10, 3 );

lib/load.php

@@ -79,6 +79,7 @@ function gutenberg_is_experiment_enabled( $name ) {
 require __DIR__ . '/full-site-editing.php';
 require __DIR__ . '/full-site-editing/default-template-types.php';
 require __DIR__ . '/full-site-editing/templates-utils.php';
+require __DIR__ . '/full-site-editing/page-templates.php';
 require __DIR__ . '/templates-sync.php';
 require __DIR__ . '/templates.php';
 require __DIR__ . '/template-parts.php';

lib/template-loader.php

@@ -63,7 +63,6 @@ function get_template_hierarchy( $template_type ) {
  */
 function gutenberg_override_query_template( $template, $type, array $templates = array() ) {
 	global $_wp_current_template_content;
-
 	$current_template = gutenberg_resolve_template( $type, $templates );
 
 	if ( $current_template ) {
@@ -215,7 +214,7 @@ function gutenberg_viewport_meta_tag() {
  * @return string Template file name without extension.
  */
 function gutenberg_strip_php_suffix( $template_file ) {
-	return preg_replace( '/\.php$/', '', $template_file );
+	return preg_replace( '/\.(php|html)$/', '', $template_file );
 }
 
 /**