Source

File: wp-includes/functions.php

function _deprecated_file( $file, $version, $replacement = '', $message = '' ) {

	/**
	 * Fires when a deprecated file is called.
	 *
	 * @since 2.5.0
	 *
	 * @param string $file        The file that was called.
	 * @param string $replacement The file that should have been included based on ABSPATH.
	 * @param string $version     The version of WordPress that deprecated the file.
	 * @param string $message     A message regarding the change.
	 */
	do_action( 'deprecated_file_included', $file, $replacement, $version, $message );

	/**
	 * Filters whether to trigger an error for deprecated files.
	 *
	 * @since 2.5.0
	 *
	 * @param bool $trigger Whether to trigger the error for deprecated files. Default true.
	 */
	if ( WP_DEBUG && apply_filters( 'deprecated_file_trigger_error', true ) ) {
		$message = empty( $message ) ? '' : ' ' . $message;

		if ( function_exists( '__' ) ) {
			if ( $replacement ) {
				trigger_error(
					sprintf(
						/* translators: 1: PHP file name, 2: Version number, 3: Alternative file name. */
						__( '%1$s is <strong>deprecated</strong> since version %2$s! Use %3$s instead.' ),
						$file,
						$version,
						$replacement
					) . $message,
					E_USER_DEPRECATED
				);
			} else {
				trigger_error(
					sprintf(
						/* translators: 1: PHP file name, 2: Version number. */
						__( '%1$s is <strong>deprecated</strong> since version %2$s with no alternative available.' ),
						$file,
						$version
					) . $message,
					E_USER_DEPRECATED
				);
			}
		} else {
			if ( $replacement ) {
				trigger_error(
					sprintf(
						'%1$s is <strong>deprecated</strong> since version %2$s! Use %3$s instead.',
						$file,
						$version,
						$replacement
					) . $message,
					E_USER_DEPRECATED
				);
			} else {
				trigger_error(
					sprintf(
						'%1$s is <strong>deprecated</strong> since version %2$s with no alternative available.',
						$file,
						$version
					) . $message,
					E_USER_DEPRECATED
				);
			}
		}
	}
}