public function enterNode(Node $node)
    {
        parent::enterNode($node);

        if (self::isConditional($node)) {
            $this->conditionalScopes++;
        } elseif ($node instanceof Function_) {
            $name = $this->getFullyQualifiedName($node->name);

            // @todo add an "else" here which adds a runtime check for instances where we can't tell
            // whether a function is being redefined by static analysis alone.
            if ($this->conditionalScopes === 0) {
                if (\function_exists($name) ||
                    isset($this->currentScope[\strtolower($name)])) {
                    $msg = \sprintf('Cannot redeclare %s()', $name);
                    throw new FatalErrorException($msg, 0, E_ERROR, null, $node->getLine());
                }
            }

            $this->currentScope[\strtolower($name)] = true;
        }
    }