fixup! cp: correct error message on copying dir to itself

src/uu/cp/src/cp.rs

@@ -1084,7 +1084,7 @@ fn copy_directory(
         return Err(format!(
             "cannot copy a directory, {}, into itself, {}",
             root.quote(),
-            root.join(target).quote()
+            target.join(root.file_name().unwrap()).quote()
         )
         .into());
     }

tests/by-util/test_cp.rs

@@ -2089,3 +2089,19 @@ fn test_copy_directory_to_itself_disallowed() {
     let expected = "cp: cannot copy a directory, 'd', into itself, 'd\\d'";
     ucmd.args(&["-R", "d", "d"]).fails().stderr_only(expected);
 }
+
+/// Test that copying a nested directory to itself is disallowed.
+#[test]
+fn test_copy_nested_directory_to_itself_disallowed() {
+    let (at, mut ucmd) = at_and_ucmd!();
+    at.mkdir("a");
+    at.mkdir("a/b");
+    at.mkdir("a/b/c");
+    #[cfg(not(windows))]
+    let expected = "cp: cannot copy a directory, 'a/b', into itself, 'a/b/c/b'";
+    #[cfg(windows)]
+    let expected = "cp: cannot copy a directory, 'a\\b', into itself, 'a\\b\\c\\b'";
+    ucmd.args(&["-R", "a/b", "a/b/c"])
+        .fails()
+        .stderr_only(expected);
+}