Prevent Variable Leakage In PHP Includes

include-me-func.php

<?php
// Use a closure so nothing leaks out when included.
return (function () {
    $array = ['foo', 'bar'];

    foreach ($array as $string) {
        // Some exciting logic.
    }
    
    return 'FOOBAR';
})();

include-me-leaky.php

<?php
// The standard leaky include.
$array = ['foo', 'bar'];

foreach ($array as $string) {
    // Some exciting logic.
}

return 'FOOBAR';

include-me-unset.php

<?php
$array = ['foo', 'bar'];

foreach ($array as $string) {
    // Some exciting logic.
}

unset($array, $string); // Unset variables so nothing leaks out when included.

return 'FOOBAR';

index.php

<?php
$returned = include __DIR__ . '/include-me-unset.php';
echo (isset($array) ? '$array variable is set' : '$array variable is not set') . PHP_EOL;
echo (isset($string) ? '$string variable is set' : '$string variable is not set') . PHP_EOL;
echo '$returned is ' . $returned . PHP_EOL;

$returned = include __DIR__ . '/include-me-func.php';
echo (isset($array) ? '$array variable is set' : '$array variable is not set') . PHP_EOL;
echo (isset($string) ? '$string variable is set' : '$string variable is not set') . PHP_EOL;
echo '$returned is ' . $returned . PHP_EOL;

$returned = (function () { return include __DIR__ . '/include-me-leaky.php'; })();
echo (isset($array) ? '$array variable is set' : '$array variable is not set') . PHP_EOL;
echo (isset($string) ? '$string variable is set' : '$string variable is not set') . PHP_EOL;
echo '$returned is ' . $returned . PHP_EOL;