REST API: Declare user capabilities using JSON Hyper Schema's "targetSchema".

There are a variety of operations a WordPress user can only perform if they have the correct capabilities. A REST API client should only display UI for one of these operations if the WordPress user can perform the operation.

Rather than requiring REST API clients to calculate whether to display UI based on potentially complicated combinations of user capabilities, `targetSchema` allows us to expose a single flag to show whether the corresponding UI should be displayed.

This change also includes flags on post objects for the following actions:

- `action-publish`: The current user can publish this post.
- `action-sticky`: The current user can make this post sticky, and the post type supports sticking.
- `action-assign-author': The current user can change the author on this post.
- `action-assign-{$taxonomy}`: The current user can assign terms from the "$taxonomy" taxonomy to this post.
- `action-create-{$taxonomy}`: The current user can create terms int the "$taxonomy" taxonomy.

Props TimothyBlynJacobs, danielbachhuber.
Fixes #44287.


Built from https://develop.svn.wordpress.org/trunk@43437


git-svn-id: http://core.svn.wordpress.org/trunk@43264 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php

@@ -368,10 +368,11 @@ class WP_REST_Attachments_Controller extends WP_REST_Posts_Controller {
 
 		$data = $this->filter_response_by_context( $data, $context );
 
+		$links = $response->get_links();
+
 		// Wrap the data in a response object.
 		$response = rest_ensure_response( $data );
-
+		$response->add_links( $links );
-		$response->add_links( $this->prepare_links( $post ) );
 
 		/**
 		 * Filters an attachment returned from the REST API.

wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php

@@ -1590,7 +1590,18 @@ class WP_REST_Posts_Controller extends WP_REST_Controller {
 		// Wrap the data in a response object.
 		$response = rest_ensure_response( $data );
 
-		$response->add_links( $this->prepare_links( $post ) );
+		$links = $this->prepare_links( $post );
+		$response->add_links( $links );
+
+		if ( ! empty( $links['self']['href'] ) ) {
+			$actions = $this->get_available_actions( $post, $request );
+
+			$self = $links['self']['href'];
+
+			foreach ( $actions as $rel ) {
+				$response->add_link( $rel, $self );
+			}
+		}
 
 		/**
 		 * Filters the post data for a response.
@@ -1729,6 +1740,60 @@ class WP_REST_Posts_Controller extends WP_REST_Controller {
 		return $links;
 	}
 
+	/**
+	 * Get the link relations available for the post and current user.
+	 *
+	 * @since 4.9.7
+	 *
+	 * @param WP_Post $post Post object.
+	 * @param WP_REST_Request Request object.
+	 *
+	 * @return array List of link relations.
+	 */
+	protected function get_available_actions( $post, $request ) {
+
+		if ( 'edit' !== $request['context'] ) {
+			return array();
+		}
+
+		$rels = array();
+
+		$post_type = get_post_type_object( $post->post_type );
+
+		if ( 'attachment' !== $this->post_type && current_user_can( $post_type->cap->publish_posts ) ) {
+			$rels[] = 'https://api.w.org/action-publish';
+		}
+
+		if ( 'post' === $post_type->name ) {
+			if ( current_user_can( $post_type->cap->edit_others_posts ) && current_user_can( $post_type->cap->publish_posts ) ) {
+				$rels[] = 'https://api.w.org/action-sticky';
+			}
+		}
+
+		if ( post_type_supports( $post_type->name, 'author' ) ) {
+			if ( current_user_can( $post_type->cap->edit_others_posts ) ) {
+				$rels[] = 'https://api.w.org/action-assign-author';
+			}
+		}
+
+		$taxonomies = wp_list_filter( get_object_taxonomies( $this->post_type, 'objects' ), array( 'show_in_rest' => true ) );
+
+		foreach ( $taxonomies as $tax ) {
+			$tax_base   = ! empty( $tax->rest_base ) ? $tax->rest_base : $tax->name;
+			$create_cap = is_taxonomy_hierarchical( $tax->name ) ? $tax->cap->edit_terms : $tax->cap->assign_terms;
+
+			if ( current_user_can( $create_cap ) ) {
+				$rels[] = 'https://api.w.org/action-create-' . $tax_base;
+			}
+
+			if ( current_user_can( $tax->cap->assign_terms ) ) {
+				$rels[] = 'https://api.w.org/action-assign-' . $tax_base;
+			}
+		}
+
+		return $rels;
+	}
+
 	/**
 	 * Retrieves the post's schema, conforming to JSON Schema.
 	 *
@@ -2069,9 +2134,125 @@ class WP_REST_Posts_Controller extends WP_REST_Controller {
 			);
 		}
 
+		$schema_links = $this->get_schema_links();
+
+		if ( $schema_links ) {
+			$schema['links'] = $schema_links;
+		}
+
 		return $this->add_additional_fields_schema( $schema );
 	}
 
+	/**
+	 * Retrieve Link Description Objects that should be added to the Schema for the posts collection.
+	 *
+	 * @since 4.9.7
+	 *
+	 * @return array
+	 */
+	protected function get_schema_links() {
+
+		$href = rest_url( "{$this->namespace}/{$this->rest_base}/{id}" );
+
+		$links = array();
+
+		if ( 'attachment' !== $this->post_type ) {
+			$links[] = array(
+				'rel'          => 'https://api.w.org/action-publish',
+				'title'        => __( 'The current user can publish this post.' ),
+				'href'         => $href,
+				'targetSchema' => array(
+					'type'       => 'object',
+					'properties' => array(
+						'status' => array(
+							'type' => 'string',
+							'enum' => array( 'publish', 'future' ),
+						),
+					),
+				),
+			);
+		}
+
+		if ( 'post' === $this->post_type ) {
+			$links[] = array(
+				'rel'          => 'https://api.w.org/action-sticky',
+				'title'        => __( 'The current user can sticky this post.' ),
+				'href'         => $href,
+				'targetSchema' => array(
+					'type'       => 'object',
+					'properties' => array(
+						'sticky' => array(
+							'type' => 'boolean',
+						),
+					),
+				),
+			);
+		}
+
+		if ( post_type_supports( $this->post_type, 'author' ) ) {
+			$links[] = array(
+				'rel'          => 'https://api.w.org/action-assign-author',
+				'title'        => __( 'The current user can change the author on this post.' ),
+				'href'         => $href,
+				'targetSchema' => array(
+					'type'       => 'object',
+					'properties' => array(
+						'author' => array(
+							'type' => 'integer',
+						),
+					),
+				),
+			);
+		}
+
+		$taxonomies = wp_list_filter( get_object_taxonomies( $this->post_type, 'objects' ), array( 'show_in_rest' => true ) );
+
+		foreach ( $taxonomies as $tax ) {
+			$tax_base = ! empty( $tax->rest_base ) ? $tax->rest_base : $tax->name;
+
+			/* translators: %s: taxonomy name */
+			$assign_title = sprintf( __( 'The current user can assign terms in the %s taxonomy.' ), $tax->name );
+			/* translators: %s: taxonomy name */
+			$create_title = sprintf( __( 'The current user can create terms in the %s taxonomy.' ), $tax->name );
+
+			$links[] = array(
+				'rel'          => 'https://api.w.org/action-assign-' . $tax_base,
+				'title'        => $assign_title,
+				'href'         => $href,
+				'targetSchema' => array(
+					'type'       => 'object',
+					'properties' => array(
+						$tax_base => array(
+							'type'  => 'array',
+							'items' => array(
+								'type' => 'integer',
+							),
+						),
+					),
+				),
+			);
+
+			$links[] = array(
+				'rel'          => 'https://api.w.org/action-create-' . $tax_base,
+				'title'        => $create_title,
+				'href'         => $href,
+				'targetSchema' => array(
+					'type'       => 'object',
+					'properties' => array(
+						$tax_base => array(
+							'type'  => 'array',
+							'items' => array(
+								'type' => 'integer',
+							),
+						),
+					),
+				),
+			);
+		}
+
+		return $links;
+	}
+
 	/**
 	 * Retrieves the query params for the posts collection.
 	 *

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.0-alpha-43436';
+$wp_version = '5.0-alpha-43437';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.