Source

File: wp-includes/rest-api/endpoints/class-wp-rest-autosaves-controller.php

public function prepare_item_for_response( $post, $request ) {

		$response = $this->revisions_controller->prepare_item_for_response( $post, $request );

		$fields = $this->get_fields_for_response( $request );

		if ( in_array( 'preview_link', $fields, true ) ) {
			$parent_id          = wp_is_post_autosave( $post );
			$preview_post_id    = false === $parent_id ? $post->ID : $parent_id;
			$preview_query_args = array();

			if ( false !== $parent_id ) {
				$preview_query_args['preview_id']    = $parent_id;
				$preview_query_args['preview_nonce'] = wp_create_nonce( 'post_preview_' . $parent_id );
			}

			$response->data['preview_link'] = get_preview_post_link( $preview_post_id, $preview_query_args );
		}

		$context        = ! empty( $request['context'] ) ? $request['context'] : 'view';
		$response->data = $this->add_additional_fields_to_object( $response->data, $request );
		$response->data = $this->filter_response_by_context( $response->data, $context );

		/**
		 * Filters a revision returned from the API.
		 *
		 * Allows modification of the revision right before it is returned.
		 *
		 * @since 5.0.0
		 *
		 * @param WP_REST_Response $response The response object.
		 * @param WP_Post          $post     The original revision object.
		 * @param WP_REST_Request  $request  Request used to generate the response.
		 */
		return apply_filters( 'rest_prepare_autosave', $response, $post, $request );
	}