class ErrorHandler

1. 8.x drupal/core/vendor/symfony/debug/Symfony/Component/Debug/ErrorHandler.php \Symfony\Component\Debug\ErrorHandler
2. 8.x drupal/core/vendor/symfony/http-kernel/Symfony/Component/HttpKernel/Debug/ErrorHandler.php \Symfony\Component\HttpKernel\Debug\ErrorHandler

ErrorHandler.php in drupal/core/vendor/symfony/http-kernel/Symfony/Component/HttpKernel/Debug/ErrorHandler.php

ErrorHandlerTest.php in drupal/core/vendor/symfony/debug/Symfony/Component/Debug/Tests/ErrorHandlerTest.php

class ErrorHandler {
  const TYPE_DEPRECATION = -100;
  private $levels = array(
    E_WARNING => 'Warning',
    E_NOTICE => 'Notice',
    E_USER_ERROR => 'User Error',
    E_USER_WARNING => 'User Warning',
    E_USER_NOTICE => 'User Notice',
    E_STRICT => 'Runtime Notice',
    E_RECOVERABLE_ERROR => 'Catchable Fatal Error',
    E_DEPRECATED => 'Deprecated',
    E_USER_DEPRECATED => 'User Deprecated',
    E_ERROR => 'Error',
    E_CORE_ERROR => 'Core Error',
    E_COMPILE_ERROR => 'Compile Error',
    E_PARSE => 'Parse',
  );
  private $level;
  private $reservedMemory;
  private $displayErrors;

  /**
   * @var LoggerInterface[] Loggers for channels
   */
  private static $loggers = array();

  /**
   * Registers the error handler.
   *
   * @param integer $level The level at which the conversion to Exception is done (null to use the error_reporting() value and 0 to disable)
   * @param Boolean $displayErrors Display errors (for dev environment) or just log they (production usage)
   *
   * @return The registered error handler
   */
  public static function register($level = null, $displayErrors = true) {
    $handler = new static();
    $handler
      ->setLevel($level);
    $handler
      ->setDisplayErrors($displayErrors);
    ini_set('display_errors', 0);
    set_error_handler(array(
      $handler,
      'handle',
    ));
    register_shutdown_function(array(
      $handler,
      'handleFatal',
    ));
    $handler->reservedMemory = str_repeat('x', 10240);
    return $handler;
  }
  public function setLevel($level) {
    $this->level = null === $level ? error_reporting() : $level;
  }
  public function setDisplayErrors($displayErrors) {
    $this->displayErrors = $displayErrors;
  }
  public static function setLogger(LoggerInterface $logger, $channel = 'deprecation') {
    self::$loggers[$channel] = $logger;
  }

  /**
   * @throws ContextErrorException When error_reporting returns error
   */
  public function handle($level, $message, $file = 'unknown', $line = 0, $context = array()) {
    if (0 === $this->level) {
      return false;
    }
    if ($level & (E_USER_DEPRECATED | E_DEPRECATED)) {
      if (isset(self::$loggers['deprecation'])) {
        if (version_compare(PHP_VERSION, '5.4', '<')) {
          $stack = array_map(function ($row) {
            unset($row['args']);
            return $row;
          }, array_slice(debug_backtrace(false), 0, 10));
        }
        else {
          $stack = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS, 10);
        }
        self::$loggers['deprecation']
          ->warning($message, array(
          'type' => self::TYPE_DEPRECATION,
          'stack' => $stack,
        ));
      }
      return true;
    }
    if ($this->displayErrors && error_reporting() & $level && $this->level & $level) {
      throw new ContextErrorException(sprintf('%s: %s in %s line %d', isset($this->levels[$level]) ? $this->levels[$level] : $level, $message, $file, $line), 0, $level, $file, $line, $context);
    }
    return false;
  }
  public function handleFatal() {
    if (null === ($error = error_get_last())) {
      return;
    }
    unset($this->reservedMemory);
    $type = $error['type'];
    if (0 === $this->level || !in_array($type, array(
      E_ERROR,
      E_CORE_ERROR,
      E_COMPILE_ERROR,
      E_PARSE,
    ))) {
      return;
    }
    if (isset(self::$loggers['emergency'])) {
      $fatal = array(
        'type' => $type,
        'file' => $error['file'],
        'line' => $error['line'],
      );
      self::$loggers['emergency']
        ->emerg($error['message'], $fatal);
    }
    if (!$this->displayErrors) {
      return;
    }

    // get current exception handler
    $exceptionHandler = set_exception_handler(function () {
    });
    restore_exception_handler();
    if (is_array($exceptionHandler) && $exceptionHandler[0] instanceof ExceptionHandler) {
      $level = isset($this->levels[$type]) ? $this->levels[$type] : $type;
      $message = sprintf('%s: %s in %s line %d', $level, $error['message'], $error['file'], $error['line']);
      $exception = new FatalErrorException($message, 0, $type, $error['file'], $error['line']);
      $exceptionHandler[0]
        ->handle($exception);
    }
  }

}