sort: failed to set message sort

src/uu/sort/src/sort.rs

@@ -1752,10 +1752,17 @@ fn default_merge_batch_size() -> usize {
     }
 }
 
+#[cfg(not(unix))]
 fn locale_failed_to_set() -> bool {
     matches!(env::var("LC_ALL").ok().as_deref(), Some("missing"))
 }
 
+#[cfg(unix)]
+fn locale_failed_to_set() -> bool {
+    use nix::libc;
+    unsafe { libc::setlocale(libc::LC_COLLATE, c"".as_ptr()).is_null() }
+}
+
 fn key_zero_width(selector: &FieldSelector) -> bool {
     let Some(to) = &selector.to else {
         return false;

tests/by-util/test_sort.rs

@@ -2733,6 +2733,21 @@ fn test_locale_utf8_sort_debug_message() {
         .stderr_contains("text ordering performed using ‘en_US.UTF-8’ sorting rules");
 }
 
+#[test]
+#[cfg(unix)]
+fn test_failed_to_set_locale_debug_message() {
+    let result = new_ucmd!()
+        .env("LC_ALL", "not-valid-locale")
+        .arg("--debug")
+        .pipe_in("a\nA\nb\nB\n")
+        .succeeds();
+
+    result.stderr_contains("text ordering performed using simple byte comparison");
+
+    #[cfg(all(target_os = "linux", target_env = "gnu"))]
+    result.stderr_contains("failed to set locale");
+}
+
 #[test]
 fn test_locale_utf8_with_key_field() {
     // Regression test for issue #10909