diff -r 3d4e9c994f10 -r a86126ab1dd4 wp/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php
--- a/wp/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php	Tue Oct 22 16:11:46 2019 +0200
+++ b/wp/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php	Tue Dec 15 13:49:49 2020 +0100
@@ -15,7 +15,6 @@
  * @see WP_REST_Controller
  */
 class WP_REST_Posts_Controller extends WP_REST_Controller {
-
 	/**
 	 * Post type.
 	 *
@@ -117,7 +116,7 @@
 						'force' => array(
 							'type'        => 'boolean',
 							'default'     => false,
-							'description' => __( 'Whether to bypass trash and force deletion.' ),
+							'description' => __( 'Whether to bypass Trash and force deletion.' ),
 						),
 					),
 				),
@@ -131,7 +130,7 @@
 	 *
 	 * @since 4.7.0
 	 *
-	 * @param  WP_REST_Request $request Full details about the request.
+	 * @param WP_REST_Request $request Full details about the request.
 	 * @return true|WP_Error True if the request has read access, WP_Error object otherwise.
 	 */
 	public function get_items_permissions_check( $request ) {
@@ -139,7 +138,11 @@
 		$post_type = get_post_type_object( $this->post_type );
 
 		if ( 'edit' === $request['context'] && ! current_user_can( $post_type->cap->edit_posts ) ) {
-			return new WP_Error( 'rest_forbidden_context', __( 'Sorry, you are not allowed to edit posts in this post type.' ), array( 'status' => rest_authorization_required_code() ) );
+			return new WP_Error(
+				'rest_forbidden_context',
+				__( 'Sorry, you are not allowed to edit posts in this post type.' ),
+				array( 'status' => rest_authorization_required_code() )
+			);
 		}
 
 		return true;
@@ -157,12 +160,20 @@
 
 		// Ensure a search string is set in case the orderby is set to 'relevance'.
 		if ( ! empty( $request['orderby'] ) && 'relevance' === $request['orderby'] && empty( $request['search'] ) ) {
-			return new WP_Error( 'rest_no_search_term_defined', __( 'You need to define a search term to order by relevance.' ), array( 'status' => 400 ) );
+			return new WP_Error(
+				'rest_no_search_term_defined',
+				__( 'You need to define a search term to order by relevance.' ),
+				array( 'status' => 400 )
+			);
 		}
 
 		// Ensure an include parameter is set in case the orderby is set to 'include'.
 		if ( ! empty( $request['orderby'] ) && 'include' === $request['orderby'] && empty( $request['include'] ) ) {
-			return new WP_Error( 'rest_orderby_include_missing_include', __( 'You need to define an include parameter to order by include.' ), array( 'status' => 400 ) );
+			return new WP_Error(
+				'rest_orderby_include_missing_include',
+				__( 'You need to define an include parameter to order by include.' ),
+				array( 'status' => 400 )
+			);
 		}
 
 		// Retrieve the list of registered collection query parameters.
@@ -234,7 +245,7 @@
 				$args['post__in'] = $args['post__in'] ? array_intersect( $sticky_posts, $args['post__in'] ) : $sticky_posts;
 
 				/*
-				 * If we intersected, but there are no post ids in common,
+				 * If we intersected, but there are no post IDs in common,
 				 * WP_Query won't return "no posts" for post__in = array()
 				 * so we have to fake it a bit.
 				 */
@@ -271,6 +282,10 @@
 
 		$taxonomies = wp_list_filter( get_object_taxonomies( $this->post_type, 'objects' ), array( 'show_in_rest' => true ) );
 
+		if ( ! empty( $request['tax_relation'] ) ) {
+			$query_args['tax_query'] = array( 'relation' => $request['tax_relation'] );
+		}
+
 		foreach ( $taxonomies as $taxonomy ) {
 			$base        = ! empty( $taxonomy->rest_base ) ? $taxonomy->rest_base : $taxonomy->name;
 			$tax_exclude = $base . '_exclude';
@@ -334,7 +349,11 @@
 		$max_pages = ceil( $total_posts / (int) $posts_query->query_vars['posts_per_page'] );
 
 		if ( $page > $max_pages && $total_posts > 0 ) {
-			return new WP_Error( 'rest_post_invalid_page_number', __( 'The page number requested is larger than the number of pages available.' ), array( 'status' => 400 ) );
+			return new WP_Error(
+				'rest_post_invalid_page_number',
+				__( 'The page number requested is larger than the number of pages available.' ),
+				array( 'status' => 400 )
+			);
 		}
 
 		$response = rest_ensure_response( $posts );
@@ -374,7 +393,12 @@
 	 * @return WP_Post|WP_Error Post object if ID is valid, WP_Error otherwise.
 	 */
 	protected function get_post( $id ) {
-		$error = new WP_Error( 'rest_post_invalid_id', __( 'Invalid post ID.' ), array( 'status' => 404 ) );
+		$error = new WP_Error(
+			'rest_post_invalid_id',
+			__( 'Invalid post ID.' ),
+			array( 'status' => 404 )
+		);
+
 		if ( (int) $id <= 0 ) {
 			return $error;
 		}
@@ -402,13 +426,21 @@
 		}
 
 		if ( 'edit' === $request['context'] && $post && ! $this->check_update_permission( $post ) ) {
-			return new WP_Error( 'rest_forbidden_context', __( 'Sorry, you are not allowed to edit this post.' ), array( 'status' => rest_authorization_required_code() ) );
+			return new WP_Error(
+				'rest_forbidden_context',
+				__( 'Sorry, you are not allowed to edit this post.' ),
+				array( 'status' => rest_authorization_required_code() )
+			);
 		}
 
 		if ( $post && ! empty( $request['password'] ) ) {
 			// Check post password, and return error if invalid.
 			if ( ! hash_equals( $post->post_password, $request['password'] ) ) {
-				return new WP_Error( 'rest_post_incorrect_password', __( 'Incorrect post password.' ), array( 'status' => 403 ) );
+				return new WP_Error(
+					'rest_post_incorrect_password',
+					__( 'Incorrect post password.' ),
+					array( 'status' => 403 )
+				);
 			}
 		}
 
@@ -490,25 +522,45 @@
 	 */
 	public function create_item_permissions_check( $request ) {
 		if ( ! empty( $request['id'] ) ) {
-			return new WP_Error( 'rest_post_exists', __( 'Cannot create existing post.' ), array( 'status' => 400 ) );
+			return new WP_Error(
+				'rest_post_exists',
+				__( 'Cannot create existing post.' ),
+				array( 'status' => 400 )
+			);
 		}
 
 		$post_type = get_post_type_object( $this->post_type );
 
 		if ( ! empty( $request['author'] ) && get_current_user_id() !== $request['author'] && ! current_user_can( $post_type->cap->edit_others_posts ) ) {
-			return new WP_Error( 'rest_cannot_edit_others', __( 'Sorry, you are not allowed to create posts as this user.' ), array( 'status' => rest_authorization_required_code() ) );
+			return new WP_Error(
+				'rest_cannot_edit_others',
+				__( 'Sorry, you are not allowed to create posts as this user.' ),
+				array( 'status' => rest_authorization_required_code() )
+			);
 		}
 
-		if ( ! empty( $request['sticky'] ) && ! current_user_can( $post_type->cap->edit_others_posts ) ) {
-			return new WP_Error( 'rest_cannot_assign_sticky', __( 'Sorry, you are not allowed to make posts sticky.' ), array( 'status' => rest_authorization_required_code() ) );
+		if ( ! empty( $request['sticky'] ) && ! current_user_can( $post_type->cap->edit_others_posts ) && ! current_user_can( $post_type->cap->publish_posts ) ) {
+			return new WP_Error(
+				'rest_cannot_assign_sticky',
+				__( 'Sorry, you are not allowed to make posts sticky.' ),
+				array( 'status' => rest_authorization_required_code() )
+			);
 		}
 
 		if ( ! current_user_can( $post_type->cap->create_posts ) ) {
-			return new WP_Error( 'rest_cannot_create', __( 'Sorry, you are not allowed to create posts as this user.' ), array( 'status' => rest_authorization_required_code() ) );
+			return new WP_Error(
+				'rest_cannot_create',
+				__( 'Sorry, you are not allowed to create posts as this user.' ),
+				array( 'status' => rest_authorization_required_code() )
+			);
 		}
 
 		if ( ! $this->check_assign_terms_permission( $request ) ) {
-			return new WP_Error( 'rest_cannot_assign_term', __( 'Sorry, you are not allowed to assign the provided terms.' ), array( 'status' => rest_authorization_required_code() ) );
+			return new WP_Error(
+				'rest_cannot_assign_term',
+				__( 'Sorry, you are not allowed to assign the provided terms.' ),
+				array( 'status' => rest_authorization_required_code() )
+			);
 		}
 
 		return true;
@@ -524,7 +576,11 @@
 	 */
 	public function create_item( $request ) {
 		if ( ! empty( $request['id'] ) ) {
-			return new WP_Error( 'rest_post_exists', __( 'Cannot create existing post.' ), array( 'status' => 400 ) );
+			return new WP_Error(
+				'rest_post_exists',
+				__( 'Cannot create existing post.' ),
+				array( 'status' => 400 )
+			);
 		}
 
 		$prepared_post = $this->prepare_item_for_database( $request );
@@ -647,19 +703,35 @@
 		$post_type = get_post_type_object( $this->post_type );
 
 		if ( $post && ! $this->check_update_permission( $post ) ) {
-			return new WP_Error( 'rest_cannot_edit', __( 'Sorry, you are not allowed to edit this post.' ), array( 'status' => rest_authorization_required_code() ) );
+			return new WP_Error(
+				'rest_cannot_edit',
+				__( 'Sorry, you are not allowed to edit this post.' ),
+				array( 'status' => rest_authorization_required_code() )
+			);
 		}
 
 		if ( ! empty( $request['author'] ) && get_current_user_id() !== $request['author'] && ! current_user_can( $post_type->cap->edit_others_posts ) ) {
-			return new WP_Error( 'rest_cannot_edit_others', __( 'Sorry, you are not allowed to update posts as this user.' ), array( 'status' => rest_authorization_required_code() ) );
+			return new WP_Error(
+				'rest_cannot_edit_others',
+				__( 'Sorry, you are not allowed to update posts as this user.' ),
+				array( 'status' => rest_authorization_required_code() )
+			);
 		}
 
-		if ( ! empty( $request['sticky'] ) && ! current_user_can( $post_type->cap->edit_others_posts ) ) {
-			return new WP_Error( 'rest_cannot_assign_sticky', __( 'Sorry, you are not allowed to make posts sticky.' ), array( 'status' => rest_authorization_required_code() ) );
+		if ( ! empty( $request['sticky'] ) && ! current_user_can( $post_type->cap->edit_others_posts ) && ! current_user_can( $post_type->cap->publish_posts ) ) {
+			return new WP_Error(
+				'rest_cannot_assign_sticky',
+				__( 'Sorry, you are not allowed to make posts sticky.' ),
+				array( 'status' => rest_authorization_required_code() )
+			);
 		}
 
 		if ( ! $this->check_assign_terms_permission( $request ) ) {
-			return new WP_Error( 'rest_cannot_assign_term', __( 'Sorry, you are not allowed to assign the provided terms.' ), array( 'status' => rest_authorization_required_code() ) );
+			return new WP_Error(
+				'rest_cannot_assign_term',
+				__( 'Sorry, you are not allowed to assign the provided terms.' ),
+				array( 'status' => rest_authorization_required_code() )
+			);
 		}
 
 		return true;
@@ -685,7 +757,7 @@
 			return $post;
 		}
 
-		// convert the post object to an array, otherwise wp_update_post will expect non-escaped input.
+		// Convert the post object to an array, otherwise wp_update_post() will expect non-escaped input.
 		$post_id = wp_update_post( wp_slash( (array) $post ), true );
 
 		if ( is_wp_error( $post_id ) ) {
@@ -776,7 +848,11 @@
 		}
 
 		if ( $post && ! $this->check_delete_permission( $post ) ) {
-			return new WP_Error( 'rest_cannot_delete', __( 'Sorry, you are not allowed to delete this post.' ), array( 'status' => rest_authorization_required_code() ) );
+			return new WP_Error(
+				'rest_cannot_delete',
+				__( 'Sorry, you are not allowed to delete this post.' ),
+				array( 'status' => rest_authorization_required_code() )
+			);
 		}
 
 		return true;
@@ -810,7 +886,7 @@
 		 *
 		 * The dynamic portion of the hook name, `$this->post_type`, refers to the post type slug.
 		 *
-		 * Pass false to disable trash support for the post.
+		 * Pass false to disable Trash support for the post.
 		 *
 		 * @since 4.7.0
 		 *
@@ -820,7 +896,11 @@
 		$supports_trash = apply_filters( "rest_{$this->post_type}_trashable", $supports_trash, $post );
 
 		if ( ! $this->check_delete_permission( $post ) ) {
-			return new WP_Error( 'rest_user_cannot_delete_post', __( 'Sorry, you are not allowed to delete this post.' ), array( 'status' => rest_authorization_required_code() ) );
+			return new WP_Error(
+				'rest_user_cannot_delete_post',
+				__( 'Sorry, you are not allowed to delete this post.' ),
+				array( 'status' => rest_authorization_required_code() )
+			);
 		}
 
 		$request->set_param( 'context', 'edit' );
@@ -839,24 +919,36 @@
 		} else {
 			// If we don't support trashing for this type, error out.
 			if ( ! $supports_trash ) {
-				/* translators: %s: force=true */
-				return new WP_Error( 'rest_trash_not_supported', sprintf( __( "The post does not support trashing. Set '%s' to delete." ), 'force=true' ), array( 'status' => 501 ) );
+				return new WP_Error(
+					'rest_trash_not_supported',
+					/* translators: %s: force=true */
+					sprintf( __( "The post does not support trashing. Set '%s' to delete." ), 'force=true' ),
+					array( 'status' => 501 )
+				);
 			}
 
 			// Otherwise, only trash if we haven't already.
 			if ( 'trash' === $post->post_status ) {
-				return new WP_Error( 'rest_already_trashed', __( 'The post has already been deleted.' ), array( 'status' => 410 ) );
+				return new WP_Error(
+					'rest_already_trashed',
+					__( 'The post has already been deleted.' ),
+					array( 'status' => 410 )
+				);
 			}
 
-			// (Note that internally this falls through to `wp_delete_post` if
-			// the trash is disabled.)
+			// (Note that internally this falls through to `wp_delete_post()`
+			// if the Trash is disabled.)
 			$result   = wp_trash_post( $id );
 			$post     = get_post( $id );
 			$response = $this->prepare_item_for_response( $post, $request );
 		}
 
 		if ( ! $result ) {
-			return new WP_Error( 'rest_cannot_delete', __( 'The post cannot be deleted.' ), array( 'status' => 500 ) );
+			return new WP_Error(
+				'rest_cannot_delete',
+				__( 'The post cannot be deleted.' ),
+				array( 'status' => 500 )
+			);
 		}
 
 		/**
@@ -866,7 +958,7 @@
 		 *
 		 * @since 4.7.0
 		 *
-		 * @param object           $post     The deleted or trashed post.
+		 * @param WP_Post          $post     The deleted or trashed post.
 		 * @param WP_REST_Response $response The response data.
 		 * @param WP_REST_Request  $request  The request sent to the API.
 		 */
@@ -956,7 +1048,7 @@
 	 * @return stdClass|WP_Error Post object or WP_Error.
 	 */
 	protected function prepare_item_for_database( $request ) {
-		$prepared_post = new stdClass;
+		$prepared_post = new stdClass();
 
 		// Post ID.
 		if ( isset( $request['id'] ) ) {
@@ -1021,21 +1113,33 @@
 
 		// Post date.
 		if ( ! empty( $schema['properties']['date'] ) && ! empty( $request['date'] ) ) {
-			$date_data = rest_get_date_with_gmt( $request['date'] );
-
-			if ( ! empty( $date_data ) ) {
+			$current_date = isset( $prepared_post->ID ) ? get_post( $prepared_post->ID )->post_date : false;
+			$date_data    = rest_get_date_with_gmt( $request['date'] );
+
+			if ( ! empty( $date_data ) && $current_date !== $date_data[0] ) {
 				list( $prepared_post->post_date, $prepared_post->post_date_gmt ) = $date_data;
 				$prepared_post->edit_date                                        = true;
 			}
 		} elseif ( ! empty( $schema['properties']['date_gmt'] ) && ! empty( $request['date_gmt'] ) ) {
-			$date_data = rest_get_date_with_gmt( $request['date_gmt'], true );
-
-			if ( ! empty( $date_data ) ) {
+			$current_date = isset( $prepared_post->ID ) ? get_post( $prepared_post->ID )->post_date_gmt : false;
+			$date_data    = rest_get_date_with_gmt( $request['date_gmt'], true );
+
+			if ( ! empty( $date_data ) && $current_date !== $date_data[1] ) {
 				list( $prepared_post->post_date, $prepared_post->post_date_gmt ) = $date_data;
 				$prepared_post->edit_date                                        = true;
 			}
 		}
 
+		// Sending a null date or date_gmt value resets date and date_gmt to their
+		// default values (`0000-00-00 00:00:00`).
+		if (
+			( ! empty( $schema['properties']['date_gmt'] ) && $request->has_param( 'date_gmt' ) && null === $request['date_gmt'] ) ||
+			( ! empty( $schema['properties']['date'] ) && $request->has_param( 'date' ) && null === $request['date'] )
+		) {
+			$prepared_post->post_date_gmt = null;
+			$prepared_post->post_date     = null;
+		}
+
 		// Post slug.
 		if ( ! empty( $schema['properties']['slug'] ) && isset( $request['slug'] ) ) {
 			$prepared_post->post_name = $request['slug'];
@@ -1049,7 +1153,11 @@
 				$user_obj = get_userdata( $post_author );
 
 				if ( ! $user_obj ) {
-					return new WP_Error( 'rest_invalid_author', __( 'Invalid author ID.' ), array( 'status' => 400 ) );
+					return new WP_Error(
+						'rest_invalid_author',
+						__( 'Invalid author ID.' ),
+						array( 'status' => 400 )
+					);
 				}
 			}
 
@@ -1062,18 +1170,30 @@
 
 			if ( '' !== $request['password'] ) {
 				if ( ! empty( $schema['properties']['sticky'] ) && ! empty( $request['sticky'] ) ) {
-					return new WP_Error( 'rest_invalid_field', __( 'A post can not be sticky and have a password.' ), array( 'status' => 400 ) );
+					return new WP_Error(
+						'rest_invalid_field',
+						__( 'A post can not be sticky and have a password.' ),
+						array( 'status' => 400 )
+					);
 				}
 
 				if ( ! empty( $prepared_post->ID ) && is_sticky( $prepared_post->ID ) ) {
-					return new WP_Error( 'rest_invalid_field', __( 'A sticky post can not be password protected.' ), array( 'status' => 400 ) );
+					return new WP_Error(
+						'rest_invalid_field',
+						__( 'A sticky post can not be password protected.' ),
+						array( 'status' => 400 )
+					);
 				}
 			}
 		}
 
 		if ( ! empty( $schema['properties']['sticky'] ) && ! empty( $request['sticky'] ) ) {
 			if ( ! empty( $prepared_post->ID ) && post_password_required( $prepared_post->ID ) ) {
-				return new WP_Error( 'rest_invalid_field', __( 'A password protected post can not be set to sticky.' ), array( 'status' => 400 ) );
+				return new WP_Error(
+					'rest_invalid_field',
+					__( 'A password protected post can not be set to sticky.' ),
+					array( 'status' => 400 )
+				);
 			}
 		}
 
@@ -1083,9 +1203,15 @@
 				$prepared_post->post_parent = 0;
 			} else {
 				$parent = get_post( (int) $request['parent'] );
+
 				if ( empty( $parent ) ) {
-					return new WP_Error( 'rest_post_invalid_id', __( 'Invalid post parent ID.' ), array( 'status' => 400 ) );
+					return new WP_Error(
+						'rest_post_invalid_id',
+						__( 'Invalid post parent ID.' ),
+						array( 'status' => 400 )
+					);
 				}
+
 				$prepared_post->post_parent = (int) $parent->ID;
 			}
 		}
@@ -1130,8 +1256,8 @@
 	 *
 	 * @since 4.7.0
 	 *
-	 * @param string $post_status Post status.
-	 * @param object $post_type   Post type.
+	 * @param string       $post_status Post status.
+	 * @param WP_Post_Type $post_type   Post type.
 	 * @return string|WP_Error Post status or WP_Error if lacking the proper permission.
 	 */
 	protected function handle_status_param( $post_status, $post_type ) {
@@ -1142,13 +1268,21 @@
 				break;
 			case 'private':
 				if ( ! current_user_can( $post_type->cap->publish_posts ) ) {
-					return new WP_Error( 'rest_cannot_publish', __( 'Sorry, you are not allowed to create private posts in this post type.' ), array( 'status' => rest_authorization_required_code() ) );
+					return new WP_Error(
+						'rest_cannot_publish',
+						__( 'Sorry, you are not allowed to create private posts in this post type.' ),
+						array( 'status' => rest_authorization_required_code() )
+					);
 				}
 				break;
 			case 'publish':
 			case 'future':
 				if ( ! current_user_can( $post_type->cap->publish_posts ) ) {
-					return new WP_Error( 'rest_cannot_publish', __( 'Sorry, you are not allowed to publish posts in this post type.' ), array( 'status' => rest_authorization_required_code() ) );
+					return new WP_Error(
+						'rest_cannot_publish',
+						__( 'Sorry, you are not allowed to publish posts in this post type.' ),
+						array( 'status' => rest_authorization_required_code() )
+					);
 				}
 				break;
 			default:
@@ -1178,7 +1312,11 @@
 			if ( $result ) {
 				return true;
 			} else {
-				return new WP_Error( 'rest_invalid_featured_media', __( 'Invalid featured media ID.' ), array( 'status' => 400 ) );
+				return new WP_Error(
+					'rest_invalid_featured_media',
+					__( 'Invalid featured media ID.' ),
+					array( 'status' => 400 )
+				);
 			}
 		} else {
 			return delete_post_thumbnail( $post_id );
@@ -1219,8 +1357,11 @@
 			return true;
 		}
 
-		/* translators: 1: parameter, 2: list of valid values */
-		return new WP_Error( 'rest_invalid_param', sprintf( __( '%1$s is not one of %2$s.' ), 'template', implode( ', ', array_keys( $allowed_templates ) ) ) );
+		return new WP_Error(
+			'rest_invalid_param',
+			/* translators: 1: Parameter, 2: List of valid values. */
+			sprintf( __( '%1$s is not one of %2$s.' ), 'template', implode( ', ', array_keys( $allowed_templates ) ) )
+		);
 	}
 
 	/**
@@ -1306,7 +1447,7 @@
 	 *
 	 * @since 4.7.0
 	 *
-	 * @param object|string $post_type Post type name or object.
+	 * @param WP_Post_Type|string $post_type Post type name or object.
 	 * @return bool Whether the post type is allowed in REST.
 	 */
 	protected function check_is_post_type_allowed( $post_type ) {
@@ -1328,7 +1469,7 @@
 	 *
 	 * @since 4.7.0
 	 *
-	 * @param object $post Post object.
+	 * @param WP_Post $post Post object.
 	 * @return bool Whether the post can be read.
 	 */
 	public function check_read_permission( $post ) {
@@ -1338,7 +1479,7 @@
 		}
 
 		// Is the post readable?
-		if ( 'publish' === $post->post_status || current_user_can( $post_type->cap->read_post, $post->ID ) ) {
+		if ( 'publish' === $post->post_status || current_user_can( 'read_post', $post->ID ) ) {
 			return true;
 		}
 
@@ -1371,7 +1512,7 @@
 	 *
 	 * @since 4.7.0
 	 *
-	 * @param object $post Post object.
+	 * @param WP_Post $post Post object.
 	 * @return bool Whether the post can be edited.
 	 */
 	protected function check_update_permission( $post ) {
@@ -1381,7 +1522,7 @@
 			return false;
 		}
 
-		return current_user_can( $post_type->cap->edit_post, $post->ID );
+		return current_user_can( 'edit_post', $post->ID );
 	}
 
 	/**
@@ -1389,7 +1530,7 @@
 	 *
 	 * @since 4.7.0
 	 *
-	 * @param object $post Post object.
+	 * @param WP_Post $post Post object.
 	 * @return bool Whether the post can be created.
 	 */
 	protected function check_create_permission( $post ) {
@@ -1407,7 +1548,7 @@
 	 *
 	 * @since 4.7.0
 	 *
-	 * @param object $post Post object.
+	 * @param WP_Post $post Post object.
 	 * @return bool Whether the post can be deleted.
 	 */
 	protected function check_delete_permission( $post ) {
@@ -1417,7 +1558,7 @@
 			return false;
 		}
 
-		return current_user_can( $post_type->cap->delete_post, $post->ID );
+		return current_user_can( 'delete_post', $post->ID );
 	}
 
 	/**
@@ -1439,19 +1580,21 @@
 		// Base fields for every post.
 		$data = array();
 
-		if ( in_array( 'id', $fields, true ) ) {
+		if ( rest_is_field_included( 'id', $fields ) ) {
 			$data['id'] = $post->ID;
 		}
 
-		if ( in_array( 'date', $fields, true ) ) {
+		if ( rest_is_field_included( 'date', $fields ) ) {
 			$data['date'] = $this->prepare_date_response( $post->post_date_gmt, $post->post_date );
 		}
 
-		if ( in_array( 'date_gmt', $fields, true ) ) {
-			// For drafts, `post_date_gmt` may not be set, indicating that the
-			// date of the draft should be updated each time it is saved (see
-			// #38883).  In this case, shim the value based on the `post_date`
-			// field with the site's timezone offset applied.
+		if ( rest_is_field_included( 'date_gmt', $fields ) ) {
+			/*
+			 * For drafts, `post_date_gmt` may not be set, indicating that the date
+			 * of the draft should be updated each time it is saved (see #38883).
+			 * In this case, shim the value based on the `post_date` field
+			 * with the site's timezone offset applied.
+			 */
 			if ( '0000-00-00 00:00:00' === $post->post_date_gmt ) {
 				$post_date_gmt = get_gmt_from_date( $post->post_date );
 			} else {
@@ -1460,7 +1603,7 @@
 			$data['date_gmt'] = $this->prepare_date_response( $post_date_gmt );
 		}
 
-		if ( in_array( 'guid', $fields, true ) ) {
+		if ( rest_is_field_included( 'guid', $fields ) ) {
 			$data['guid'] = array(
 				/** This filter is documented in wp-includes/post-template.php */
 				'rendered' => apply_filters( 'get_the_guid', $post->guid, $post->ID ),
@@ -1468,50 +1611,54 @@
 			);
 		}
 
-		if ( in_array( 'modified', $fields, true ) ) {
+		if ( rest_is_field_included( 'modified', $fields ) ) {
 			$data['modified'] = $this->prepare_date_response( $post->post_modified_gmt, $post->post_modified );
 		}
 
-		if ( in_array( 'modified_gmt', $fields, true ) ) {
-			// For drafts, `post_modified_gmt` may not be set (see
-			// `post_date_gmt` comments above).  In this case, shim the value
-			// based on the `post_modified` field with the site's timezone
-			// offset applied.
+		if ( rest_is_field_included( 'modified_gmt', $fields ) ) {
+			/*
+			 * For drafts, `post_modified_gmt` may not be set (see `post_date_gmt` comments
+			 * above). In this case, shim the value based on the `post_modified` field
+			 * with the site's timezone offset applied.
+			 */
 			if ( '0000-00-00 00:00:00' === $post->post_modified_gmt ) {
-				$post_modified_gmt = date( 'Y-m-d H:i:s', strtotime( $post->post_modified ) - ( get_option( 'gmt_offset' ) * 3600 ) );
+				$post_modified_gmt = gmdate( 'Y-m-d H:i:s', strtotime( $post->post_modified ) - ( get_option( 'gmt_offset' ) * 3600 ) );
 			} else {
 				$post_modified_gmt = $post->post_modified_gmt;
 			}
 			$data['modified_gmt'] = $this->prepare_date_response( $post_modified_gmt );
 		}
 
-		if ( in_array( 'password', $fields, true ) ) {
+		if ( rest_is_field_included( 'password', $fields ) ) {
 			$data['password'] = $post->post_password;
 		}
 
-		if ( in_array( 'slug', $fields, true ) ) {
+		if ( rest_is_field_included( 'slug', $fields ) ) {
 			$data['slug'] = $post->post_name;
 		}
 
-		if ( in_array( 'status', $fields, true ) ) {
+		if ( rest_is_field_included( 'status', $fields ) ) {
 			$data['status'] = $post->post_status;
 		}
 
-		if ( in_array( 'type', $fields, true ) ) {
+		if ( rest_is_field_included( 'type', $fields ) ) {
 			$data['type'] = $post->post_type;
 		}
 
-		if ( in_array( 'link', $fields, true ) ) {
+		if ( rest_is_field_included( 'link', $fields ) ) {
 			$data['link'] = get_permalink( $post->ID );
 		}
 
-		if ( in_array( 'title', $fields, true ) ) {
+		if ( rest_is_field_included( 'title', $fields ) ) {
+			$data['title'] = array();
+		}
+		if ( rest_is_field_included( 'title.raw', $fields ) ) {
+			$data['title']['raw'] = $post->post_title;
+		}
+		if ( rest_is_field_included( 'title.rendered', $fields ) ) {
 			add_filter( 'protected_title_format', array( $this, 'protected_title_format' ) );
 
-			$data['title'] = array(
-				'raw'      => $post->post_title,
-				'rendered' => get_the_title( $post->ID ),
-			);
+			$data['title']['rendered'] = get_the_title( $post->ID );
 
 			remove_filter( 'protected_title_format', array( $this, 'protected_title_format' ) );
 		}
@@ -1525,19 +1672,30 @@
 			$has_password_filter = true;
 		}
 
-		if ( in_array( 'content', $fields, true ) ) {
-			$data['content'] = array(
-				'raw'           => $post->post_content,
-				/** This filter is documented in wp-includes/post-template.php */
-				'rendered'      => post_password_required( $post ) ? '' : apply_filters( 'the_content', $post->post_content ),
-				'protected'     => (bool) $post->post_password,
-				'block_version' => block_version( $post->post_content ),
-			);
+		if ( rest_is_field_included( 'content', $fields ) ) {
+			$data['content'] = array();
+		}
+		if ( rest_is_field_included( 'content.raw', $fields ) ) {
+			$data['content']['raw'] = $post->post_content;
+		}
+		if ( rest_is_field_included( 'content.rendered', $fields ) ) {
+			/** This filter is documented in wp-includes/post-template.php */
+			$data['content']['rendered'] = post_password_required( $post ) ? '' : apply_filters( 'the_content', $post->post_content );
 		}
-
-		if ( in_array( 'excerpt', $fields, true ) ) {
+		if ( rest_is_field_included( 'content.protected', $fields ) ) {
+			$data['content']['protected'] = (bool) $post->post_password;
+		}
+		if ( rest_is_field_included( 'content.block_version', $fields ) ) {
+			$data['content']['block_version'] = block_version( $post->post_content );
+		}
+
+		if ( rest_is_field_included( 'excerpt', $fields ) ) {
 			/** This filter is documented in wp-includes/post-template.php */
-			$excerpt         = apply_filters( 'the_excerpt', apply_filters( 'get_the_excerpt', $post->post_excerpt, $post ) );
+			$excerpt = apply_filters( 'get_the_excerpt', $post->post_excerpt, $post );
+
+			/** This filter is documented in wp-includes/post-template.php */
+			$excerpt = apply_filters( 'the_excerpt', $excerpt );
+
 			$data['excerpt'] = array(
 				'raw'       => $post->post_excerpt,
 				'rendered'  => post_password_required( $post ) ? '' : $excerpt,
@@ -1550,43 +1708,44 @@
 			remove_filter( 'post_password_required', '__return_false' );
 		}
 
-		if ( in_array( 'author', $fields, true ) ) {
+		if ( rest_is_field_included( 'author', $fields ) ) {
 			$data['author'] = (int) $post->post_author;
 		}
 
-		if ( in_array( 'featured_media', $fields, true ) ) {
+		if ( rest_is_field_included( 'featured_media', $fields ) ) {
 			$data['featured_media'] = (int) get_post_thumbnail_id( $post->ID );
 		}
 
-		if ( in_array( 'parent', $fields, true ) ) {
+		if ( rest_is_field_included( 'parent', $fields ) ) {
 			$data['parent'] = (int) $post->post_parent;
 		}
 
-		if ( in_array( 'menu_order', $fields, true ) ) {
+		if ( rest_is_field_included( 'menu_order', $fields ) ) {
 			$data['menu_order'] = (int) $post->menu_order;
 		}
 
-		if ( in_array( 'comment_status', $fields, true ) ) {
+		if ( rest_is_field_included( 'comment_status', $fields ) ) {
 			$data['comment_status'] = $post->comment_status;
 		}
 
-		if ( in_array( 'ping_status', $fields, true ) ) {
+		if ( rest_is_field_included( 'ping_status', $fields ) ) {
 			$data['ping_status'] = $post->ping_status;
 		}
 
-		if ( in_array( 'sticky', $fields, true ) ) {
+		if ( rest_is_field_included( 'sticky', $fields ) ) {
 			$data['sticky'] = is_sticky( $post->ID );
 		}
 
-		if ( in_array( 'template', $fields, true ) ) {
-			if ( $template = get_page_template_slug( $post->ID ) ) {
+		if ( rest_is_field_included( 'template', $fields ) ) {
+			$template = get_page_template_slug( $post->ID );
+			if ( $template ) {
 				$data['template'] = $template;
 			} else {
 				$data['template'] = '';
 			}
 		}
 
-		if ( in_array( 'format', $fields, true ) ) {
+		if ( rest_is_field_included( 'format', $fields ) ) {
 			$data['format'] = get_post_format( $post->ID );
 
 			// Fill in blank post format.
@@ -1595,7 +1754,7 @@
 			}
 		}
 
-		if ( in_array( 'meta', $fields, true ) ) {
+		if ( rest_is_field_included( 'meta', $fields ) ) {
 			$data['meta'] = $this->meta->get_value( $post->ID, $request );
 		}
 
@@ -1604,7 +1763,7 @@
 		foreach ( $taxonomies as $taxonomy ) {
 			$base = ! empty( $taxonomy->rest_base ) ? $taxonomy->rest_base : $taxonomy->name;
 
-			if ( in_array( $base, $fields, true ) ) {
+			if ( rest_is_field_included( $base, $fields ) ) {
 				$terms         = get_the_terms( $post, $taxonomy->name );
 				$data[ $base ] = $terms ? array_values( wp_list_pluck( $terms, 'term_id' ) ) : array();
 			}
@@ -1612,18 +1771,23 @@
 
 		$post_type_obj = get_post_type_object( $post->post_type );
 		if ( is_post_type_viewable( $post_type_obj ) && $post_type_obj->public ) {
-
-			if ( ! function_exists( 'get_sample_permalink' ) ) {
-				require_once ABSPATH . 'wp-admin/includes/post.php';
-			}
-
-			$sample_permalink = get_sample_permalink( $post->ID, $post->post_title, '' );
-
-			if ( in_array( 'permalink_template', $fields, true ) ) {
-				$data['permalink_template'] = $sample_permalink[0];
-			}
-			if ( in_array( 'generated_slug', $fields, true ) ) {
-				$data['generated_slug'] = $sample_permalink[1];
+			$permalink_template_requested = rest_is_field_included( 'permalink_template', $fields );
+			$generated_slug_requested     = rest_is_field_included( 'generated_slug', $fields );
+
+			if ( $permalink_template_requested || $generated_slug_requested ) {
+				if ( ! function_exists( 'get_sample_permalink' ) ) {
+					require_once ABSPATH . 'wp-admin/includes/post.php';
+				}
+
+				$sample_permalink = get_sample_permalink( $post->ID, $post->post_title, '' );
+
+				if ( $permalink_template_requested ) {
+					$data['permalink_template'] = $sample_permalink[0];
+				}
+
+				if ( $generated_slug_requested ) {
+					$data['generated_slug'] = $sample_permalink[1];
+				}
 			}
 		}
 
@@ -1747,7 +1911,8 @@
 		}
 
 		// If we have a featured media, add that.
-		if ( $featured_media = get_post_thumbnail_id( $post->ID ) ) {
+		$featured_media = get_post_thumbnail_id( $post->ID );
+		if ( $featured_media ) {
 			$image_url = rest_url( 'wp/v2/media/' . $featured_media );
 
 			$links['https://api.w.org/featuredmedia'] = array(
@@ -1802,9 +1967,8 @@
 	 *
 	 * @since 4.9.8
 	 *
-	 * @param WP_Post $post Post object.
-	 * @param WP_REST_Request Request object.
-	 *
+	 * @param WP_Post         $post    Post object.
+	 * @param WP_REST_Request $request Request object.
 	 * @return array List of link relations.
 	 */
 	protected function get_available_actions( $post, $request ) {
@@ -1863,6 +2027,9 @@
 	 * @return array Item schema data.
 	 */
 	public function get_item_schema() {
+		if ( $this->schema ) {
+			return $this->add_additional_fields_schema( $this->schema );
+		}
 
 		$schema = array(
 			'$schema'    => 'http://json-schema.org/draft-04/schema#',
@@ -1872,13 +2039,13 @@
 			'properties' => array(
 				'date'         => array(
 					'description' => __( "The date the object was published, in the site's timezone." ),
-					'type'        => 'string',
+					'type'        => array( 'string', 'null' ),
 					'format'      => 'date-time',
 					'context'     => array( 'view', 'edit', 'embed' ),
 				),
 				'date_gmt'     => array(
 					'description' => __( 'The date the object was published, as GMT.' ),
-					'type'        => 'string',
+					'type'        => array( 'string', 'null' ),
 					'format'      => 'date-time',
 					'context'     => array( 'view', 'edit' ),
 				),
@@ -2025,6 +2192,7 @@
 				'custom-fields',
 			),
 		);
+
 		foreach ( $post_type_attributes as $attribute ) {
 			if ( isset( $fixed_schemas[ $this->post_type ] ) && ! in_array( $attribute, $fixed_schemas[ $this->post_type ], true ) ) {
 				continue;
@@ -2040,8 +2208,8 @@
 						'type'        => 'object',
 						'context'     => array( 'view', 'edit', 'embed' ),
 						'arg_options' => array(
-							'sanitize_callback' => null, // Note: sanitization implemented in self::prepare_item_for_database()
-							'validate_callback' => null, // Note: validation implemented in self::prepare_item_for_database()
+							'sanitize_callback' => null, // Note: sanitization implemented in self::prepare_item_for_database().
+							'validate_callback' => null, // Note: validation implemented in self::prepare_item_for_database().
 						),
 						'properties'  => array(
 							'raw'      => array(
@@ -2065,8 +2233,8 @@
 						'type'        => 'object',
 						'context'     => array( 'view', 'edit' ),
 						'arg_options' => array(
-							'sanitize_callback' => null, // Note: sanitization implemented in self::prepare_item_for_database()
-							'validate_callback' => null, // Note: validation implemented in self::prepare_item_for_database()
+							'sanitize_callback' => null, // Note: sanitization implemented in self::prepare_item_for_database().
+							'validate_callback' => null, // Note: validation implemented in self::prepare_item_for_database().
 						),
 						'properties'  => array(
 							'raw'           => array(
@@ -2110,8 +2278,8 @@
 						'type'        => 'object',
 						'context'     => array( 'view', 'edit', 'embed' ),
 						'arg_options' => array(
-							'sanitize_callback' => null, // Note: sanitization implemented in self::prepare_item_for_database()
-							'validate_callback' => null, // Note: validation implemented in self::prepare_item_for_database()
+							'sanitize_callback' => null, // Note: sanitization implemented in self::prepare_item_for_database().
+							'validate_callback' => null, // Note: validation implemented in self::prepare_item_for_database().
 						),
 						'properties'  => array(
 							'raw'       => array(
@@ -2203,10 +2371,27 @@
 		);
 
 		$taxonomies = wp_list_filter( get_object_taxonomies( $this->post_type, 'objects' ), array( 'show_in_rest' => true ) );
+
 		foreach ( $taxonomies as $taxonomy ) {
-			$base                          = ! empty( $taxonomy->rest_base ) ? $taxonomy->rest_base : $taxonomy->name;
+			$base = ! empty( $taxonomy->rest_base ) ? $taxonomy->rest_base : $taxonomy->name;
+
+			if ( array_key_exists( $base, $schema['properties'] ) ) {
+				$taxonomy_field_name_with_conflict = ! empty( $taxonomy->rest_base ) ? 'rest_base' : 'name';
+				_doing_it_wrong(
+					'register_taxonomy',
+					sprintf(
+						/* translators: 1. The taxonomy name, 2. The property name, either 'rest_base' or 'name', 3. The conflicting value. */
+						__( 'The "%1$s" taxonomy "%2$s" property (%3$s) conflicts with an existing property on the REST API Posts Controller. Specify a custom "rest_base" when registering the taxonomy to avoid this error.' ),
+						$taxonomy->name,
+						$taxonomy_field_name_with_conflict,
+						$base
+					),
+					'5.4.0'
+				);
+			}
+
 			$schema['properties'][ $base ] = array(
-				/* translators: %s: taxonomy name */
+				/* translators: %s: Taxonomy name. */
 				'description' => sprintf( __( 'The terms assigned to the object in the %s taxonomy.' ), $taxonomy->name ),
 				'type'        => 'array',
 				'items'       => array(
@@ -2222,7 +2407,38 @@
 			$schema['links'] = $schema_links;
 		}
 
-		return $this->add_additional_fields_schema( $schema );
+		// Take a snapshot of which fields are in the schema pre-filtering.
+		$schema_fields = array_keys( $schema['properties'] );
+
+		/**
+		 * Filter the post's schema.
+		 *
+		 * The dynamic portion of the filter, `$this->post_type`, refers to the
+		 * post type slug for the controller.
+		 *
+		 * @since 5.4.0
+		 *
+		 * @param array $schema Item schema data.
+		 */
+		$schema = apply_filters( "rest_{$this->post_type}_item_schema", $schema );
+
+		// Emit a _doing_it_wrong warning if user tries to add new properties using this filter.
+		$new_fields = array_diff( array_keys( $schema['properties'] ), $schema_fields );
+		if ( count( $new_fields ) > 0 ) {
+			_doing_it_wrong(
+				__METHOD__,
+				sprintf(
+					/* translators: %s: register_rest_field */
+					__( 'Please use %s to add new schema properties.' ),
+					'register_rest_field'
+				),
+				'5.4.0'
+			);
+		}
+
+		$this->schema = $schema;
+
+		return $this->add_additional_fields_schema( $this->schema );
 	}
 
 	/**
@@ -2308,9 +2524,9 @@
 		foreach ( $taxonomies as $tax ) {
 			$tax_base = ! empty( $tax->rest_base ) ? $tax->rest_base : $tax->name;
 
-			/* translators: %s: taxonomy name */
+			/* translators: %s: Taxonomy name. */
 			$assign_title = sprintf( __( 'The current user can assign terms in the %s taxonomy.' ), $tax->name );
-			/* translators: %s: taxonomy name */
+			/* translators: %s: Taxonomy name. */
 			$create_title = sprintf( __( 'The current user can create terms in the %s taxonomy.' ), $tax->name );
 
 			$links[] = array(
@@ -2496,11 +2712,19 @@
 
 		$taxonomies = wp_list_filter( get_object_taxonomies( $this->post_type, 'objects' ), array( 'show_in_rest' => true ) );
 
+		if ( ! empty( $taxonomies ) ) {
+			$query_params['tax_relation'] = array(
+				'description' => __( 'Limit result set based on relationship between multiple taxonomies.' ),
+				'type'        => 'string',
+				'enum'        => array( 'AND', 'OR' ),
+			);
+		}
+
 		foreach ( $taxonomies as $taxonomy ) {
 			$base = ! empty( $taxonomy->rest_base ) ? $taxonomy->rest_base : $taxonomy->name;
 
 			$query_params[ $base ] = array(
-				/* translators: %s: taxonomy name */
+				/* translators: %s: Taxonomy name. */
 				'description' => sprintf( __( 'Limit result set to all items that have the specified term assigned in the %s taxonomy.' ), $base ),
 				'type'        => 'array',
 				'items'       => array(
@@ -2510,7 +2734,7 @@
 			);
 
 			$query_params[ $base . '_exclude' ] = array(
-				/* translators: %s: taxonomy name */
+				/* translators: %s: Taxonomy name. */
 				'description' => sprintf( __( 'Limit result set to all items except those that have the specified term assigned in the %s taxonomy.' ), $base ),
 				'type'        => 'array',
 				'items'       => array(
@@ -2551,15 +2775,15 @@
 	 *
 	 * @since 4.7.0
 	 *
-	 * @param  string|array    $statuses  One or more post statuses.
-	 * @param  WP_REST_Request $request   Full details about the request.
-	 * @param  string          $parameter Additional parameter to pass to validation.
+	 * @param string|array    $statuses  One or more post statuses.
+	 * @param WP_REST_Request $request   Full details about the request.
+	 * @param string          $parameter Additional parameter to pass to validation.
 	 * @return array|WP_Error A list of valid statuses, otherwise WP_Error object.
 	 */
 	public function sanitize_post_statuses( $statuses, $request, $parameter ) {
 		$statuses = wp_parse_slug_list( $statuses );
 
-		// The default status is different in WP_REST_Attachments_Controller
+		// The default status is different in WP_REST_Attachments_Controller.
 		$attributes     = $request->get_attributes();
 		$default_status = $attributes['args']['status']['default'];
 
@@ -2576,7 +2800,11 @@
 					return $result;
 				}
 			} else {
-				return new WP_Error( 'rest_forbidden_status', __( 'Status is forbidden.' ), array( 'status' => rest_authorization_required_code() ) );
+				return new WP_Error(
+					'rest_forbidden_status',
+					__( 'Status is forbidden.' ),
+					array( 'status' => rest_authorization_required_code() )
+				);
 			}
 		}