The behaviour of hexadecimal numeric strings was inconsistent prior to PHP 7 and support has been removed in PHP 7

PHP Compatibility Code

PHPCompatibility.Miscellaneous.ValidIntegers.HexNumericStringFound

Recommendation

We manually go through all the occurrences and decide whether it's meant to be used as a simple string or as a number. Replace valid hex numbers with integers or hexdec, add PHPCodeSniffer exceptions for the false positives.

Example with Integer Replacement

$value = '0xff';
if (is_numeric($value)) {
}

Because the hexadecimal value is hardcoded, it might be simplest to replace it with its hardcoded decimal counterpart.

$value = 255;
if (is_numeric($value)) {
}

Example With hexdec Conversion

$value = $data['hex'];
if (is_numeric($value)) {
}

Since we don't know what the value would be in advance, we would convert it to a decimal first.

$value = hexdec($data['hex']);
if (is_numeric($value)) {
}

However, since we have no guarantee that $data['hex'] is a valid hexadecimal string, a more complete example would look like this. Follow the guide PSR-0 Autoloading to load the Compatibility_Php56 into the legacy project.

final class Compatibility_Php56
{
    public static function hexStringToDec($value)
    {
        if (!preg_match('/^0x[0-9a-fA-F]+$/', $value)) {
            return 0;
        }
        
        return hexdec($value);
    }
}

$value = Compatibility_Php56::hexStringToDec($data['hex']);
if (is_numeric($value)) {
    echo $value;
}

We check whether it's a valid hexadecimal string. In PHP 5.6, a string that is not hexadecimal would be converted to zero, so that 1 + 'ff' would produce 1. If it's a valid hexadecimal string, we convert it to a decimal, so that 1 + '0xff' would produce 256.

Exclude False Positives

If a string starts with 0x by pure coincidence, which is extremely rare, then we might just need to add an exception to the phpcs.xml file that is used in generating the PHP Compatibility report.

<?xml version="1.0"?>
<ruleset>
    <rule ref="PHPCompatibility.Miscellaneous.ValidIntegers.HexNumericStringFound">
        <exclude-pattern>/path/to/file.php</exclude-pattern>
        <exclude-pattern>/path/to/folder/*.php</exclude-pattern>
    </rule>
</ruleset>