sort: disable -o with -C and -c

src/uu/sort/src/sort.rs

@@ -1198,12 +1198,14 @@ pub fn uu_app() -> App<'static, 'static> {
                     options::check::QUIET,
                     options::check::DIAGNOSE_FIRST,
                 ])
+                .conflicts_with(options::OUTPUT)
                 .help("check for sorted input; do not sort"),
         )
         .arg(
             Arg::with_name(options::check::CHECK_SILENT)
                 .short("C")
                 .long(options::check::CHECK_SILENT)
+                .conflicts_with(options::OUTPUT)
                 .help("exit successfully if the given file is already sorted, and exit with status 1 otherwise."),
         )
         .arg(

tests/by-util/test_sort.rs

@@ -941,3 +941,17 @@ fn test_sigpipe_panic() {
         Ok(String::new())
     );
 }
+
+#[test]
+fn test_conflict_check_out() {
+    let check_flags = ["-c=silent", "-c=quiet", "-c=diagnose-first", "-c", "-C"];
+    for check_flag in &check_flags {
+        new_ucmd!()
+            .arg(check_flag)
+            .arg("-o=/dev/null")
+            .fails()
+            .stderr_contains(
+                "error: The argument '--output <FILENAME>' cannot be used with '--check",
+            );
+    }
+}