fix(metadata set): return error when both --datasource-filepath and -datasource-ls are used (#16049)

# Description

This PR improves the `metadata set` command by returning a clear error
when both `--datasource-filepath` and `--datasource-ls` flags are used
together. These flags are meant to be mutually exclusive, and previously
this conflicting usage was silently ignored.

# User-Facing Changes

* Users will now see an error message if they use both
`--datasource-filepath` and `--datasource-ls` together in `metadata
set`.

# Tests + Formatting

* [x] Added test at
`crates/nu-command/tests/commands/debug/metadata_set.rs` to verify the
error behavior.
* [x] Ran `cargo fmt --all -- --check`
* [x] Ran `cargo clippy --workspace -- -D warnings -D
clippy::unwrap_used`
* [x] Ran `cargo test --workspace`


# After Submitting

N/A

crates/nu-command/src/debug/metadata.rs

@@ -43,6 +43,17 @@ impl Command for Metadata {
         let arg = call.positional_nth(stack, 0);
         let head = call.head;
 
+        if !matches!(input, PipelineData::Empty) {
+            if let Some(arg_expr) = arg {
+                return Err(ShellError::IncompatibleParameters {
+                    left_message: "pipeline input was provided".into(),
+                    left_span: head,
+                    right_message: "but a positional metadata expression was also given".into(),
+                    right_span: arg_expr.span,
+                });
+            }
+        }
+
         match arg {
             Some(Expression {
                 expr: Expr::FullCellPath(full_cell_path),
@@ -56,7 +67,6 @@ impl Command for Metadata {
                             ..
                         } => {
                             let origin = stack.get_var_with_origin(*var_id, *span)?;
-
                             Ok(build_metadata_record_value(
                                 &origin,
                                 input.metadata().as_ref(),

crates/nu-command/src/debug/metadata_set.rs

@@ -63,7 +63,18 @@ impl Command for MetadataSet {
         match (ds_fp, ds_ls) {
             (Some(path), false) => metadata.data_source = DataSource::FilePath(path.into()),
             (None, true) => metadata.data_source = DataSource::Ls,
-            (Some(_), true) => (), // TODO: error here
+            (Some(_), true) => {
+                return Err(ShellError::IncompatibleParameters {
+                    left_message: "cannot use `--datasource-filepath`".into(),
+                    left_span: call
+                        .get_flag_span(stack, "datasource-filepath")
+                        .expect("has flag"),
+                    right_message: "with `--datasource-ls`".into(),
+                    right_span: call
+                        .get_flag_span(stack, "datasource-ls")
+                        .expect("has flag"),
+                });
+            }
             (None, false) => (),
         }
 

crates/nu-command/tests/commands/debug/metadata_set.rs

@@ -0,0 +1,43 @@
+use nu_test_support::nu;
+use nu_test_support::pipeline;
+
+#[test]
+fn errors_on_conflicting_metadata_flags() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+        echo "foo" | metadata set --datasource-filepath foo.txt --datasource-ls
+        "#
+    ));
+
+    assert!(actual.err.contains("cannot use `--datasource-filepath`"));
+    assert!(actual.err.contains("with `--datasource-ls`"));
+}
+
+#[test]
+fn works_with_datasource_filepath() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+        echo "foo"
+        | metadata set --datasource-filepath foo.txt
+        | metadata
+        "#
+    ));
+
+    assert!(actual.out.contains("foo.txt"));
+}
+
+#[test]
+fn works_with_datasource_ls() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+        echo "foo"
+        | metadata set --datasource-ls
+        | metadata
+        "#
+    ));
+
+    assert!(actual.out.contains("ls"));
+}

crates/nu-command/tests/commands/debug/mod.rs

@@ -1 +1,2 @@
+mod metadata_set;
 mod timeit;