PHP eval代码沙箱中断

Question

I noticed a heavily downvoted comment in here: http://php.net/manual/en/function.php-check-syntax.php

function eval_syntax($code)
{
    $braces = 0;
    $inString = 0;

    // We need to know if braces are correctly balanced.
    // This is not trivial due to variable interpolation
    // which occurs in heredoc, backticked and double quoted strings
    foreach (token_get_all('<?php ' . $code) as $token)
    {
        if (is_array($token))
        {
            switch ($token[0])
            {
            case T_CURLY_OPEN:
            case T_DOLLAR_OPEN_CURLY_BRACES:
            case T_START_HEREDOC: ++$inString; break;
            case T_END_HEREDOC:   --$inString; break;
            }
        }
        else if ($inString & 1)
        {
            switch ($token)
            {
            case '`':
            case '"': --$inString; break;
            }
        }
        else
        {
            switch ($token)
            {
            case '`':
            case '"': ++$inString; break;

            case '{': ++$braces; break;
            case '}':
                if ($inString) --$inString;
                else
                {
                    --$braces;
                    if ($braces < 0) return false;
                }

                break;
            }
        }
    }

    // If $braces is not zero, then we are sure that $code is broken.
    // We run it anyway in order to catch the error message and line number.

    // Else, if $braces are correctly balanced, then we can safely put
    // $code in a dead code sandbox to prevent its execution.
    // Note that without this sandbox, a function or class declaration inside
    // $code could throw a "Cannot redeclare" fatal error.

    echo "Braces: ".$braces."
";
    $braces || $code = "if(0){{$code}
}";

    if (false === eval($code)) {}
}

eval_syntax("file_put_contents('/home/yourname/Desktop/done.txt', 'OVERWRITTEN');");

I tried to bypass the code to maliciously execute user-input, but I couldn't. I wonder why it got downvoted.

As you can see if curly brackets are not matching, it doesn't add the 'if(0){' . $code . '} and executes the user input with mismatching curly brackets which will throw exception and won't really run.

If curly brackets are a match, it calls the eval, but its inside a if {0} "sandbox". How can someone bypass this?

I know eval is insecure, but I want to know what's the trick here. How can you bypass security of if (0) and braces check in the code above?

You can try directly the code from php.net or my minified/edited version above. Point is proving that this code is not secure and user an execute arbitrary PHP Code