timeout: exit with 128+9 when the timeout signal is KILL

identified here https://efraingaray.com/en/blog/rust-coreutils-contra-gnu/

src/uu/timeout/src/timeout.rs

@@ -309,7 +309,12 @@ fn timeout(
             report_if_verbose(signal, &cmd[0], verbose);
             platform::send_signal(process, signal, foreground, None, &spawn_state);
 
-            if let Some(kill_after) = kill_after {
+            // KILL cannot be caught, so a later kill is pointless and the
+            // exit status reports the signal instead of the timeout.
+            let sent_kill = signal_by_name_or_value("KILL") == Some(signal);
+            if let Some(kill_after) = kill_after
+                && !sent_kill
+            {
                 return match wait_or_kill_process(
                     process,
                     &cmd[0],
@@ -337,6 +342,8 @@ fn timeout(
                     })
                     .unwrap_or_else(|| ExitStatus::CommandTimedOut.into());
                 Err(exit_code.into())
+            } else if sent_kill {
+                Err(ExitStatus::SignalSent(signal).into())
             } else {
                 Err(ExitStatus::CommandTimedOut.into())
             }

tests/by-util/test_timeout.rs

@@ -130,6 +130,31 @@ fn test_kill_after_preserves_timeout_exit_without_preserve_status() {
         .fails_with_code(124)
         .no_output();
 }
+
+/// A timeout signal of KILL reports 128 + 9 rather than 124, with or
+/// without `--kill-after`; other signals keep reporting 124.
+#[test]
+fn test_kill_signal_reports_signal_exit_code() {
+    let (ts, bin) = scenario_with_bin();
+    for args in [
+        &["-s", "KILL", ".05"][..],
+        &["--signal=9", ".05"],
+        &["-s", "SIGKILL", "--kill-after=3", ".05"],
+        // Only the child is signaled here, but the status is still 128+9.
+        &["--foreground", "-s", "KILL", ".05"],
+    ] {
+        ts.ucmd()
+            .args(args)
+            .args(&[bin.as_str(), "sleep", "20"])
+            .fails_with_code(128 + 9)
+            .no_output();
+    }
+    ts.ucmd()
+        .args(&["-s", "HUP", ".05", &bin, "sleep", "20"])
+        .fails_with_code(124)
+        .no_output();
+}
+
 #[test]
 fn test_preserve_status_even_when_send_signal() {
     let (ts, bin) = scenario_with_bin();