The error handler isn't executing until the error happens and that's long after scope has left the setErrorHandler() method. It cannot know what you meant by "static".

Specify the class name.

  set_error_handler(__CLASS__ . '::_errorHandler'); // or get_called_class()

Then you'll get an error about being unable to call a protected method, which you can resolve by making _errorHandler() public.

OK. I understood. Class scope should be on calling time instead of registering time.

Yes I can make the way that your solution. Going to be a little dirty.

It works like following

<?php

namespace My;

class Exception extends \Exception
{
    protected $context;
    
    public static function setErrorHandler()
    {
        set_error_handler('static::_errorHandler');
    }
    
    public static function restoreErrorHandler()
    {
        return restore_error_handler();
    }
    
    protected static function _errorHandler($number, $message, $file, $line, $context)
    {
        self::restoreErrorHandler();

        $exception = new static($message, $number);
        $exception->file = $file;
        $exception->line = $line;
        $exception->context = $context;

        throw $exception;
    }
    
    public static function triggerError($message)
    {
        trigger_error($message);
    }
}

\My\Exception::setErrorHandler();

try {
    \My\Exception::triggerError('My custom error!');
} catch (\My\Exception $ex) {
    echo $ex->getMessage();
}



\My\Exception::restoreErrorHandler();