Detect broken setlocale on musl

Author: nikic

ext/standard/config.m4

@@ -368,6 +368,24 @@ if test "$ac_cv_strptime_decl_fails" = "yes"; then
   AC_DEFINE([HAVE_STRPTIME_DECL_FAILS], 1, [whether strptime() declaration fails])
 fi
 
+dnl musl has a badly broken setlocale() implementation that always reports success.
+AC_CACHE_CHECK([whether setlocale() is broken], ac_cv_setlocale_broken, [
+AC_RUN_IFELSE([AC_LANG_SOURCE([[
+#include <locale.h>
+int main() {
+    return setlocale(LC_CTYPE, "This locale certainly does not exist") == NULL;
+}
+]])],[
+  ac_cv_setlocale_broken=yes
+],[
+  ac_cv_setlocale_broken=no
+],[
+  ac_cv_setlocale_broken=no
+])])
+if test "$ac_cv_setlocale_broken" = "yes"; then
+  AC_DEFINE([HAVE_BROKEN_SETLOCALE], 1, [whether setlocale() is broken])
+fi
+
 dnl
 dnl Check for arc4random on BSD systems
 dnl

ext/standard/string.c

@@ -4662,6 +4662,15 @@ PHP_FUNCTION(setlocale)
 
 # ifndef PHP_WIN32
 		retval = php_my_setlocale(cat, loc ? ZSTR_VAL(loc) : NULL);
+#  if HAVE_BROKEN_SETLOCALE
+		/* musl libc always reports success for setlocale().
+		 * Manually whitelist the allowed locales "", "C" and "C.UTF-8" instead. */
+		if (retval && loc && ZSTR_LEN(loc) != 0
+				&& !zend_string_equals_literal(loc, "C")
+				&& !zend_string_equals_literal(loc, "C.UTF-8")) {
+			retval = NULL;
+		}
+#  endif
 # else
 		if (loc) {
 			/* BC: don't try /^[a-z]{2}_[A-Z]{2}($|\..*)/ except for /^u[ks]_U[KS]$/ */