Add 'overlay new' command (#5647)

* Add 'overlay new' command

* Add missing file

crates/nu-command/src/core_commands/overlay/mod.rs

@@ -1,9 +1,11 @@
 mod add;
 mod command;
 mod list;
+mod new;
 mod remove;
 
 pub use add::OverlayAdd;
 pub use command::Overlay;
 pub use list::OverlayList;
+pub use new::OverlayNew;
 pub use remove::OverlayRemove;

crates/nu-command/src/core_commands/overlay/new.rs

@@ -0,0 +1,74 @@
+use nu_engine::CallExt;
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EngineState, Stack};
+use nu_protocol::{Category, Example, PipelineData, ShellError, Signature, Spanned, SyntaxShape};
+
+#[derive(Clone)]
+pub struct OverlayNew;
+
+impl Command for OverlayNew {
+    fn name(&self) -> &str {
+        "overlay new"
+    }
+
+    fn usage(&self) -> &str {
+        "Create an empty overlay"
+    }
+
+    fn signature(&self) -> nu_protocol::Signature {
+        Signature::build("overlay new")
+            .required("name", SyntaxShape::String, "Name of the overlay")
+            // TODO:
+            // .switch(
+            //     "prefix",
+            //     "Prepend module name to the imported symbols",
+            //     Some('p'),
+            // )
+            .category(Category::Core)
+    }
+
+    fn extra_usage(&self) -> &str {
+        r#"The command will first create an empty module, then add it as an overlay.
+
+This command is a parser keyword. For details, check:
+  https://www.nushell.sh/book/thinking_in_nushell.html"#
+    }
+
+    fn is_parser_keyword(&self) -> bool {
+        true
+    }
+
+    fn run(
+        &self,
+        engine_state: &EngineState,
+        stack: &mut Stack,
+        call: &Call,
+        _input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        let name_arg: Spanned<String> = call.req(engine_state, stack, 0)?;
+
+        stack.add_overlay(name_arg.item);
+
+        Ok(PipelineData::new(call.head))
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            description: "Create an empty overlay",
+            example: r#"overlay new spam"#,
+            result: None,
+        }]
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_examples() {
+        use crate::test_examples;
+
+        test_examples(OverlayNew {})
+    }
+}