PHP `str_contains()` polyfill

str_contains.php

<?php

if (!function_exists('str_contains')) {
    /**
     * Determine if a string contains a given substring
     *
     * @link https://www.php.net/manual/en/function.str-contains.php PHP `str_contains` original document.
     * @param string $haystack The string to search in.
     * @param string $needle The substring to search for in the `haystack`.
     * @return bool Returns `true` if `needle` is in `haystack`, `false` otherwise.
     */
    function str_contains($haystack, $needle) {
        // verify type and show the errors as in PHP 8.
        if (!is_scalar($haystack)) {
            trigger_error('Argument #1 ($haystack) must be of type string, ' . gettype($haystack) . ' given', E_USER_ERROR);
        }
        if (!is_scalar($needle)) {
            trigger_error('Argument #2 ($needle) must be of type string, ' . gettype($needle) . ' given', E_USER_ERROR);
        }

        return '' === $needle || false === $needle || false !== mb_strpos($haystack, $needle);
        // note:
        // empty string and `false` always return `true` in PHP 8.0+.
        // `true`, float (or double) type must be check with `mb_strpos()` instead of `strpos()`.
    }
}

tests.php

<?php

$string = '123abcกขคょよら㑆㑇㑈456.78';

echo 'haystack is ' . $string . '<br>';
echo 'false, true, empty<br>';
var_dump(str_contains($string, false));// true
var_dump(str_contains($string, true));// false
var_dump(str_contains($string, ''));// true
echo 'contains strings<br>';
var_dump(str_contains($string, 'a'));// true
var_dump(str_contains($string, 'aa'));// false
var_dump(str_contains($string, 'z'));// false
var_dump(str_contains($string, 'ก'));// true
var_dump(str_contains($string, 'กก'));// false
var_dump(str_contains($string, 'ฮ'));// false
var_dump(str_contains($string, 'ょ'));// true
var_dump(str_contains($string, 'ょょ'));// false
var_dump(str_contains($string, 'ゖ'));// false
var_dump(str_contains($string, '㑆'));// true
var_dump(str_contains($string, '㑆㑆'));// false
var_dump(str_contains($string, '㔩'));// false
echo 'contains 0 &amp; 1<br>';
var_dump(str_contains($string, 0));// false
var_dump(str_contains($string, 1));// true
echo 'contains numbers (float, double)<br>';
var_dump(str_contains($string, 123.0));// true (required mb_strpos)
var_dump(str_contains($string, 456.78));// true (required mb_strpos)
echo 'haystack is true. check contains false, true, empty<br>';
var_dump(str_contains(true, false));// true
var_dump(str_contains(true, true));// true (required mb_strpos)
var_dump(str_contains(true, ''));// true
echo 'haystack is false. check contains false, true, empty<br>';
var_dump(str_contains(false, false));// true
var_dump(str_contains(false, true));// false
var_dump(str_contains(false, ''));// true
echo 'haystack is empty. check contains false, true, empty<br>';
var_dump(str_contains('', false));// true
var_dump(str_contains('', true));// false
var_dump(str_contains('', ''));// true
echo 'error!<br>';
var_dump(str_contains($string, ['a']));
echo 'can\'t continue here.<br>';