ucp: Change error when directory is specified but not recursive (#10609)

# Description
Closes #10537. Basically error message was unhelpful, and this temporary
measure adds back the nice previous nushell error message. Ideally, we
would like to add a more permanent solution mentioned in the issue
[comments](https://github.com/nushell/nushell/issues/10537#issuecomment-1743686122),
but since we want to have `ucp` as `cp` on new release, this is hackier
but way simpler so this fix should do it.

Only downside is that now behavior differs from `uutils` in the sense
that:
```
uutils:
> cp a foo/ bar
ls bar
# foo/a

nushell:
>ucp a foo/ bar
# directory error (not copied) ....
```
So, since its non fatal error, uutils copies a, but nushell errors out
with nothing copied. If we go to option 3 mentioned above, then we can
decide what we want to do, and perhaps continue on a non fatal error.


# User-Facing Changes
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helps us keep track of breaking changes. -->

# Tests + Formatting
Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- [X] `cargo fmt --all -- --check` to check standard code formatting
(`cargo fmt --all` applies these changes)
- [X] `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used`
to check that you're using the standard code style
- [X] `cargo test --workspace` to check that all tests pass (on Windows
make sure to [enable developer
mode](https://learn.microsoft.com/en-us/windows/apps/get-started/developer-mode-features-and-debugging))
- [X] `cargo run -- -c "use std testing; testing run-tests --path
crates/nu-std"` to run the tests for the standard library

> **Note**
> from `nushell` you can also use the `toolkit` as follows
> ```bash
> use toolkit.nu # or use an `env_change` hook to activate it
automatically
> toolkit check pr
> ```

# After Submitting

---------

Co-authored-by: amtoine <stevan.antoine@gmail.com>

crates/nu-command/src/filesystem/ucp.rs

@@ -166,6 +166,17 @@ impl Command for UCp {
                         if f.is_empty() {
                             return Err(ShellError::FileNotFound(p.span));
                         }
+                        let any_source_is_dir = f.iter().any(|f| matches!(f, f if f.is_dir()));
+                        if any_source_is_dir && !recursive {
+                            return Err(ShellError::GenericError(
+                                "could_not_copy_directory".into(),
+                                "resolves to a directory (not copied)".into(),
+                                Some(p.span),
+                                Some("Directories must be copied using \"--recursive\"".into()),
+                                Vec::new(),
+                            ));
+                        }
+
                         Ok(f)
                     }
                     Err(e) => Err(ShellError::GenericError(

crates/nu-command/tests/commands/ucp.rs

@@ -91,15 +91,8 @@ fn error_if_attempting_to_copy_a_directory_to_another_directory_impl(progress: b
             dirs.test().display()
         );
 
-        // Changing to GNU error like error
+        assert!(actual.err.contains("formats"));
-        // Slight bug since it should say formats, but its saying "." due to the `strip_prefix`
+        assert!(actual.err.contains("resolves to a directory (not copied)"));
-        // that i do I think
-        // assert!(actual.err.contains("formats"));
-        // assert!(actual.err.contains("resolves to a directory (not copied)"));
-        assert!(actual.err.contains("omitting directory"));
-
-        // directories must be copied using --recursive
-        // gnu says "omitting directory", vbecause -r was not given
     });
 }