[php-src] Issue #24552: Case-insensitive substr_compare, ksort, krsort are still locale-dependent

Issue: https://github.com/php/php-src/issues/24552 Author: sirreal ### Description The following code: ```php <?php foreach (['C', 'tr_TR.UTF-8'] as $locale) { if (setlocale(LC_CTYPE, $locale) === false) { throw new RuntimeException("Locale unavailable: $locale"); } $values = ['I', 'h']; sort($values, SORT_STRING | SORT_FLAG_CASE); $keys = ['I' => 0, 'h' => 0]; ksort($keys, SORT_STRING | SORT_FLAG_CASE); echo $locale, "\n"; echo ' stripos: ', var_export(stripos('I', 'i'), true), "\n"; echo ' strncasecmp: ', strncasecmp('I', 'i', 1), "\n"; echo ' substr_compare: ', substr_compare('I', 'i', 0, 1, true), "\n"; echo ' sort: ', implode(',', $values), "\n"; echo ' ksort: ', implode(',', array_keys($keys)), "\n"; } ``` Resulted in this output: ``` C stripos: 0 strncasecmp: 0 substr_compare: 0 sort: h,I ksort: h,I tr_TR.UTF-8 stripos: 0 strncasecmp: 0 substr_compare: -32 sort: h,I ksort: I,h ``` But I expected this output instead: ``` C stripos: 0 strncasecmp: 0 substr_compare: 0 sort: h,I ksort: h,I tr_TR.UTF-8 stripos: 0 strncasecmp: 0 substr_compare: 0 sort: h,I ksort: h,I ``` [Reproduction link](https://3v4l.org/8A33E) --- PHP 8.2 switched strtolower(), stripos(), sort() with SORT_STRING | SORT_FLAG_CASE [#](https://www.php.net/manual/en/array.constants.php#constant.sort-flag-case) and related functions to ASCII case conversion, but substr_compare() with $case_insensitive = true and ksort()/krsort() with SORT_STRING | SORT_FLAG_CASE still follow LC_CTYPE. The output above is from PHP 8.2.35, 8.3.36, 8.4.27 and 8.5.12. PHP 8.1.34 prints the same, except that stripos() and sort() also follow the locale (false and I,h). 8.2 changed those two but not substr_compare() or ksort(). <details> <summary>Reproducing on PHP 8.1 to 8.5 with Docker</summary> The official php:*-cli images have no tr_TR.UTF-8 locale, so each run generates it first. With the snippet above saved as repro.php: ```sh for v in 8.1 8.2 8.3 8.4 8.5; do docker run --rm -i "php:$v-cli" sh -c ' apt-get update -qq >/dev/null && apt-get install -y -qq locales >/dev/null 2>&1 && localedef -i tr_TR -f UTF-8 tr_TR.UTF-8 && php -v | head -n 1 && php' < repro.php done ``` </details> The 8.2 [UPGRADING](https://github.com/php/php-src/blob/PHP-8.2/UPGRADING) notes say sorting with SORT_FLAG_CASE uses ASCII case conversion, and the [strtolower-ascii RFC](https://wiki.php.net/rfc/strtolower-ascii) says case-insensitive substr_compare() already did. On master, substr_compare() calls zend_binary_strncasecmp_l(), and php_array_key_compare_string_case_unstable_i(), which ksort() and krsort() use, calls zend_binary_strcasecmp_l(). Both helpers fold case with zend_tolower(), which is the C library's tolower() and follows LC_CTYPE. Under glibc's tr_TR.UTF-8, tolower('I') is 'I'. Switching these two call sites to zend_binary_strncasecmp() and zend_binary_strcasecmp() would give the documented behavior. See https://github.com/php/php-src/pull/7506. ### PHP Version ```plain PHP 8.5.12 (cli) (built: Oct 21 2026 15:53:40) (NTS) Copyright (c) The PHP Group Built by https://github.com/docker-library/php Zend Engine v4.5.12, Copyright (c) Zend Technologies with Zend OPcache v8.5.12, Copyright (c), by Zend Technologies ``` ### Operating System Debian GNU/Linux 13 (trixie), glibc 2.41 (php:8.5-cli Docker image)