WordPress at a glance
function is not described

WP_REST_Posts_Controller::check_template() public WP 4.9.0

Check whether the template is valid for the given post.

{} It's a method of the class: WP_REST_Posts_Controller{}

No Hooks.

Return

true/false/WP_Error. True if template is still valid or if the same as existing value, or false if template not supported.

Usage

$WP_REST_Posts_Controller = new WP_REST_Posts_Controller();
$WP_REST_Posts_Controller->check_template( $template, $request );
$template(string) (required)
Page template filename.
$request(WP_REST_Request) (required)
Request.

Changelog

Since 4.9.0 Introduced.

Code of WP_REST_Posts_Controller::check_template() WP 5.5.1

<?php
public function check_template( $template, $request ) {

	if ( ! $template ) {
		return true;
	}

	if ( $request['id'] ) {
		$current_template = get_page_template_slug( $request['id'] );
	} else {
		$current_template = '';
	}

	// Always allow for updating a post to the same template, even if that template is no longer supported.
	if ( $template === $current_template ) {
		return true;
	}

	// If this is a create request, get_post() will return null and wp theme will fallback to the passed post type.
	$allowed_templates = wp_get_theme()->get_page_templates( get_post( $request['id'] ), $this->post_type );

	if ( isset( $allowed_templates[ $template ] ) ) {
		return true;
	}

	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 ) ) )
	);
}