cp: only allow directory for -t

src/uu/cp/src/cp.rs

@@ -315,6 +315,12 @@ pub fn uu_app<'a>() -> App<'a> {
              .long(options::TARGET_DIRECTORY)
              .value_name(options::TARGET_DIRECTORY)
              .takes_value(true)
+             .validator(|s| {
+                 if Path::new(s).is_dir() {
+                     return Ok(());
+                 }
+                 Err("must specify a directory")
+             })
              .help("copy all SOURCE arguments into target-directory"))
         .arg(Arg::new(options::NO_TARGET_DIRECTORY)
              .short('T')

tests/by-util/test_cp.rs

@@ -183,6 +183,16 @@ fn test_cp_arg_no_target_directory() {
         .stderr_contains("cannot overwrite directory");
 }
 
+#[test]
+fn test_cp_target_directory_is_file() {
+    new_ucmd!()
+        .arg("-t")
+        .arg(TEST_HOW_ARE_YOU_SOURCE)
+        .arg(TEST_HELLO_WORLD_SOURCE)
+        .fails()
+        .stderr_contains("must specify a directory");
+}
+
 #[test]
 fn test_cp_arg_interactive() {
     new_ucmd!()