REST API: Include `viewable` attribute on Post Type resource for `edit` context.

For the block editor to be able to expose the Preview button correctly, it needs to know the `is_post_type_viewable()` setting, this change adds it to the Post Type response.

Props danielbachhuber.
Merges [43007] to the 4.9 branch.
Fixes #43739.
Built from https://develop.svn.wordpress.org/branches/4.9@43038


git-svn-id: http://core.svn.wordpress.org/branches/4.9@42867 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/rest-api/endpoints/class-wp-rest-post-types-controller.php

@@ -155,6 +155,7 @@ class WP_REST_Post_Types_Controller extends WP_REST_Controller {
 			'capabilities' => $post_type->cap,
 			'description'  => $post_type->description,
 			'hierarchical' => $post_type->hierarchical,
+			'viewable'     => is_post_type_viewable( $post_type ),
 			'labels'       => $post_type->labels,
 			'name'         => $post_type->label,
 			'slug'         => $post_type->name,
@@ -223,6 +224,12 @@ class WP_REST_Post_Types_Controller extends WP_REST_Controller {
 					'context'      => array( 'view', 'edit' ),
 					'readonly'     => true,
 				),
+				'viewable'         => array(
+					'description'  => __( 'Whether or not the post type can be viewed.' ),
+					'type'         => 'boolean',
+					'context'      => array( 'edit' ),
+					'readonly'     => true,
+				),
 				'labels'           => array(
 					'description'  => __( 'Human-readable labels for the post type for various contexts.' ),
 					'type'         => 'object',

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.9.6-alpha-43037';
+$wp_version = '4.9.6-alpha-43038';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.