split: directory separator in additional suffix

src/uu/split/src/filenames.rs

@@ -40,6 +40,7 @@ use crate::{
 };
 use clap::ArgMatches;
 use std::fmt;
+use std::path::is_separator;
 use uucore::display::Quotable;
 use uucore::error::{UResult, USimpleError};
 
@@ -230,7 +231,7 @@ impl Suffix {
             .get_one::<String>(OPT_ADDITIONAL_SUFFIX)
             .unwrap()
             .to_string();
-        if additional.contains('/') || additional.contains('\\') {
+        if additional.chars().any(is_separator) {
             return Err(SuffixError::ContainsSeparator(additional));
         }
 

tests/by-util/test_split.rs

@@ -247,11 +247,14 @@ fn test_split_additional_suffix() {
 }
 
 #[test]
-fn test_additional_suffix_no_slash() {
+fn test_additional_suffix_dir_separator() {
+    #[cfg(unix)]
     new_ucmd!()
         .args(&["--additional-suffix", "a/b"])
         .fails()
         .usage_error("invalid suffix 'a/b', contains directory separator");
+
+    #[cfg(windows)]
     new_ucmd!()
         .args(&["--additional-suffix", "a\\b"])
         .fails()