bug(cp): like gnu/cp, don't show any message when --no-clobber is used

Simple example:
touch bar
rm -rf /tmp/foo
mkdir -p /tmp/foo
cp -pnL -v bar /tmp/foo
echo $?
cp -pnL -v bar /tmp/foo
echo $?

rm -rf /tmp/foo
mkdir -p /tmp/foo
./target/debug/coreutils cp -pnL -v bar /tmp/foo
echo $?
./target/debug/coreutils cp -pnL bar /tmp/foo
echo $?

src/uu/cp/src/cp.rs

@@ -814,10 +814,17 @@ fn copy(sources: &[Source], target: &Target, options: &Options) -> CopyResult<()
             }
             if !found_hard_link {
                 if let Err(error) = copy_source(source, target, &target_type, options) {
-                    show_error!("{}", error);
                     match error {
-                        Error::Skipped(_) => (),
-                        _ => non_fatal_errors = true,
+                        // When using --no-clobber, we don't want to show
+                        // an error message
+                        Error::NotAllFilesCopied => (),
+                        Error::Skipped(_) => {
+                            show_error!("{}", error);
+                        }
+                        _ => {
+                            show_error!("{}", error);
+                            non_fatal_errors = true
+                        }
                     }
                 }
             }
@@ -993,11 +1000,7 @@ fn copy_directory(root: &Path, target: &Target, options: &Options) -> CopyResult
 impl OverwriteMode {
     fn verify(&self, path: &Path) -> CopyResult<()> {
         match *self {
-            OverwriteMode::NoClobber => Err(Error::Skipped(format!(
-                "Not overwriting {} because of option '{}'",
-                path.display(),
-                OPT_NO_CLOBBER
-            ))),
+            OverwriteMode::NoClobber => Err(Error::NotAllFilesCopied),
             OverwriteMode::Interactive(_) => {
                 if prompt_yes!("{}: overwrite {}? ", executable!(), path.display()) {
                     Ok(())

tests/by-util/test_cp.rs

@@ -255,7 +255,40 @@ fn test_cp_arg_no_clobber() {
 
     assert!(result.success);
     assert_eq!(at.read(TEST_HOW_ARE_YOU_SOURCE), "How are you?\n");
-    assert!(result.stderr.contains("Not overwriting"));
+}
+
+#[test]
+fn test_cp_arg_no_clobber_twice() {
+    let scene = TestScenario::new(util_name!());
+    let at = &scene.fixtures;
+    at.touch("source.txt");
+    let result = scene
+        .ucmd()
+        .arg("--no-clobber")
+        .arg("source.txt")
+        .arg("dest.txt")
+        .run();
+
+    println!("stderr = {:?}", result.stderr);
+    println!("stdout = {:?}", result.stdout);
+    assert!(result.success);
+    assert!(result.stderr.is_empty());
+    assert_eq!(at.read("source.txt"), "");
+
+    at.append("source.txt", "some-content");
+    let result = scene
+        .ucmd()
+        .arg("--no-clobber")
+        .arg("source.txt")
+        .arg("dest.txt")
+        .run();
+
+    assert!(result.success);
+    assert_eq!(at.read("source.txt"), "some-content");
+    // Should be empty as the "no-clobber" should keep
+    // the previous version
+    assert_eq!(at.read("dest.txt"), "");
+    assert!(!result.stderr.contains("Not overwriting"));
 }
 
 #[test]