Don't throw for out of bounds offsets in strspn()

Make strspn($str1, $str2, $offset, $length) behaviorally
equivalent to strspn(substr($str1, $offset, $length), $str2)
by not throwing for out of bounds offset.

There have been two reports that this change cause issues,
including bug #80285.

UPGRADING

@@ -532,8 +532,6 @@ PHP 8.0 UPGRADE NOTES
   . parse_str() can no longer be used without specifying a result array.
   . fgetss() has been removed.
   . The string.strip_tags filter has been removed.
-  . strspn() and strcspn() now throw a ValueError when the start or length
-    argument exceed the bounds of the string.
   . The needle argument of strpos(), strrpos(), stripos(), strripos(), strstr(),
     strchr(), strrchr(), and stristr() will now always be interpreted as a
     string. Previously non-string needles were interpreted as an ASCII code

ext/standard/string.c

@@ -258,22 +258,25 @@ static void php_spn_common_handler(INTERNAL_FUNCTION_PARAMETERS, int behavior) /
 		Z_PARAM_LONG_OR_NULL(len, len_is_null)
 	ZEND_PARSE_PARAMETERS_END();
 
+	size_t remain_len = ZSTR_LEN(s11);
 	if (start < 0) {
-		start += (zend_long)ZSTR_LEN(s11);
-	}
-	if (start < 0 || (size_t)start > ZSTR_LEN(s11)) {
-		zend_argument_value_error(3, "must be contained in argument #1 ($str)");
-		RETURN_THROWS();
+		start += remain_len;
+		if (start < 0) {
+			start = 0;
+		}
+	} else if ((size_t) start > remain_len) {
+		start = remain_len;
 	}
 
-	size_t remain_len = ZSTR_LEN(s11) - start;
+	remain_len -= start;
 	if (!len_is_null) {
 		if (len < 0) {
 			len += remain_len;
-		}
-		if (len < 0 || (size_t)len > remain_len) {
-			zend_argument_value_error(4, "must be contained in argument #1 ($str)");
-			RETURN_THROWS();
+			if (len < 0) {
+				len = 0;
+			}
+		} else if ((size_t) len > remain_len) {
+			len = remain_len;
 		}
 	} else {
 		len = remain_len;

ext/standard/tests/strings/bug40754.phpt

@@ -7,18 +7,8 @@ $v = 2147483647;
 
 var_dump(substr("abcde", 1, $v));
 var_dump(substr_replace("abcde", "x", $v, $v));
-
-try {
-    var_dump(strspn("abcde", "abc", $v, $v));
-} catch (ValueError $exception) {
-    echo $exception->getMessage() . "\n";
-}
-
-try {
-    var_dump(strcspn("abcde", "abc", $v, $v));
-} catch (ValueError $exception) {
-    echo $exception->getMessage() . "\n";
-}
+var_dump(strspn("abcde", "abc", $v, $v));
+var_dump(strcspn("abcde", "abc", $v, $v));
 
 try {
     var_dump(substr_count("abcde", "abc", $v, $v));
@@ -88,8 +78,8 @@ var_dump(substr("abcde", $v, $v));
 --EXPECT--
 string(4) "bcde"
 string(6) "abcdex"
-strspn(): Argument #3 ($offset) must be contained in argument #1 ($str)
-strcspn(): Argument #3 ($offset) must be contained in argument #1 ($str)
+int(0)
+int(0)
 substr_count(): Argument #3 ($offset) must be contained in argument #1 ($haystack)
 substr_compare(): Argument #3 ($offset) must be contained in argument #1 ($main_str)
 stripos(): Argument #3 ($offset) must be contained in argument #1 ($haystack)

ext/standard/tests/strings/strcspn.phpt

@@ -9,16 +9,12 @@ var_dump($b);
 var_dump(strcspn($a,$b));
 var_dump(strcspn($a,$b,9));
 var_dump(strcspn($a,$b,9,6));
-try {
-    var_dump(strcspn('a', 'B', 1, 2147483647));
-} catch (ValueError $e) {
-    echo $e->getMessage(), "\n";
-}
+var_dump(strcspn('a', 'B', 1, 2147483647));
 ?>
 --EXPECT--
 string(25) "22222222aaaa bbb1111 cccc"
 string(4) "1234"
 int(0)
 int(7)
 int(6)
-strcspn(): Argument #4 ($length) must be contained in argument #1 ($str)
+int(0)