Add available page templates REST field and selector to sidebar

codecov.yml

@@ -0,0 +1,2 @@
+comment:
+  require_changes: true

gutenberg.php

@@ -24,6 +24,7 @@
 	require_once dirname( __FILE__ ) . '/lib/i18n.php';
 	require_once dirname( __FILE__ ) . '/lib/parser.php';
 	require_once dirname( __FILE__ ) . '/lib/register.php';
+	require_once dirname( __FILE__ ) . '/lib/rest-api.php';
 
 	// Register server-side code for individual blocks.
 	require_once dirname( __FILE__ ) . '/lib/blocks/latest-posts.php';

lib/rest-api.php

@@ -0,0 +1,67 @@
+<?php
+/**
+ * REST API Extensions.
+ *
+ * @package gutenberg
+ */
+
+if ( ! defined( 'ABSPATH' ) ) {
+	die( 'Silence is golden.' );
+}
+
+/**
+ * Registers REST field for `available_page_templates` on page resources.
+ *
+ * @since 0.7.0
+ *
+ * @return void
+ */
+function gutenberg_register_available_page_templates_field() {
+	register_rest_field( 'page', 'available_page_templates', array(
+		'get_callback' => 'gutenberg_get_available_page_templates',
+		'schema' => array(
+			'description' => __( 'Available templates for a given page.', 'gutenberg' ),
+			'type' => 'array',
+			'items' => array(
+				'type' => 'object',
+				'properties' => array(
+					'name' => array(
+						'type' => 'string',
+						'description' => __( 'Template name', 'gutenberg' ),
+					),
+					'template' => array(
+						'type' => 'string',
+						'description' => __( 'Template slug', 'gutenberg' ),
+					),
+				),
+			),
+			'readonly' => true,
+			'context' => array( 'edit' ),
+		),
+	) );
+}
+add_action( 'rest_api_init', 'gutenberg_register_available_page_templates_field' );
+
+/**
+ * Returns available page templates for a requested page..
+ *
+ * @since 0.7.0
+ * @see gutenberg_register_available_page_templates_field()
+ *
+ * @param array $page Page data.
+ * @return array Available page templates.
+ */
+function gutenberg_get_available_page_templates( $page ) {
+	$available_templates = array();
+
+	// No page templates are available if the post is the page on front. See page_attributes_meta_box().
+	if ( intval( get_option( 'page_for_posts' ) ) === $page['id'] ) {
+		return array();
+	}
+
+	$page_templates = wp_get_theme()->get_page_templates( $page['id'] );
+	foreach ( $page_templates as $template => $name ) {
+		$available_templates[] = compact( 'name', 'template' );
+	}
+	return $available_templates;
+}