code: public static function addDebugEntries(array $formattedError, $e, $debug)
      {
          if (! $debug) {
              return $formattedError;
          }
  
          Utils::invariant(
              $e instanceof Exception || $e instanceof Throwable,
              'Expected exception, got %s',
              Utils::getVariableType($e)
          );
  
          $debug = (int) $debug;
  
          if ($debug & Debug::RETHROW_INTERNAL_EXCEPTIONS) {
              if (! $e instanceof Error) {
                  throw $e;
              }
  
              if ($e->getPrevious()) {
                  throw $e->getPrevious();
              }
          }
  
          $isUnsafe = ! $e instanceof ClientAware || ! $e->isClientSafe();
  
          if (($debug & Debug::RETHROW_UNSAFE_EXCEPTIONS) && $isUnsafe) {
              if ($e->getPrevious()) {
                  throw $e->getPrevious();
              }
          }
  
          if (($debug & Debug::INCLUDE_DEBUG_MESSAGE) && $isUnsafe) {
              // Displaying debugMessage as a first entry:
              $formattedError = ['debugMessage' => $e->getMessage()] + $formattedError;
          }
  
          if ($debug & Debug::INCLUDE_TRACE) {
              if ($e instanceof ErrorException || $e instanceof \Error) {
                  $formattedError += [
                      'file' => $e->getFile(),
                      'line' => $e->getLine(),
                  ];
              }
  
              $isTrivial = $e instanceof Error && ! $e->getPrevious();
  
              if (! $isTrivial) {
                  $debugging               = $e->getPrevious() ?: $e;
                  $formattedError['trace'] = static::toSafeTrace($debugging);
              }
          }
  
          return $formattedError;
      }
docs: Decorates spec-compliant $formattedError with debug entries according to $debug flags
  (see GraphQL\Error\Debug for available flags)
  
  @param mixed[]   $formattedError
  @param Throwable $e
  @param bool|int  $debug
  
  @return mixed[]
  
  @throws Throwable