Error handler with WordPress backtrace in message.

backtrace-error-handler.php

<?php

set_error_handler( 'backtrace_error_handler', error_reporting() );

function backtrace_error_handler( $errno, $errstr, $errfile, $errline, $errcontext ) {

	// handle @
	if( 0 === error_reporting() )
		return false;

	$message = $errstr . ' in ' . $errfile . ' on line ' . $errline . ', backtrace: ' . wp_debug_backtrace_summary( null, 1 );

	if( WP_DEBUG_DISPLAY || ini_get( 'display_errors' ) )
		echo '<br />' . $message . '<br />';

	if( WP_DEBUG_LOG || ini_get( 'log_errors' ) )
		error_log( $message );

	return false;
}