split $nu variable into scope commands and simpler $nu (#9487)

# Description

This splits off `scope` from `$nu`, creating a set of `scope` commands
for the various types of scope you might be interested in.

This also simplifies the `$nu` variable a bit.

# User-Facing Changes

This changes `$nu` to be a bit simpler and introduces a set of `scope`
subcommands.

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

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

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
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- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect -A clippy::result_large_err` to check that
you're using the standard code style
- `cargo test --workspace` to check that all tests pass
- `cargo run -- crates/nu-std/tests/run.nu` 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
<!-- If your PR had any user-facing changes, update [the
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crates/nu-cmd-lang/src/core_commands/mod.rs

@@ -30,6 +30,7 @@ mod module;
 mod mut_;
 pub(crate) mod overlay;
 mod return_;
+mod scope;
 mod try_;
 mod use_;
 mod version;
@@ -67,6 +68,7 @@ pub use module::Module;
 pub use mut_::Mut;
 pub use overlay::*;
 pub use return_::Return;
+pub use scope::*;
 pub use try_::Try;
 pub use use_::Use;
 pub use version::Version;

crates/nu-cmd-lang/src/core_commands/scope/aliases.rs

@@ -0,0 +1,62 @@
+use nu_engine::scope::ScopeData;
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EngineState, Stack};
+use nu_protocol::{
+    Category, Example, IntoInterruptiblePipelineData, PipelineData, ShellError, Signature, Type,
+};
+
+#[derive(Clone)]
+pub struct ScopeAliases;
+
+impl Command for ScopeAliases {
+    fn name(&self) -> &str {
+        "scope aliases"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("scope aliases")
+            .input_output_types(vec![(Type::Nothing, Type::Any)])
+            .allow_variants_without_examples(true)
+            .category(Category::Filters)
+    }
+
+    fn usage(&self) -> &str {
+        "Output info on the aliases in the current scope."
+    }
+
+    fn run(
+        &self,
+        engine_state: &EngineState,
+        stack: &mut Stack,
+        call: &Call,
+        _input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        let span = call.head;
+        let ctrlc = engine_state.ctrlc.clone();
+
+        let mut scope_data = ScopeData::new(engine_state, stack);
+        scope_data.populate_all();
+
+        Ok(scope_data.collect_aliases(span).into_pipeline_data(ctrlc))
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            description: "Show the aliases in the current scope",
+            example: "scope aliases",
+            result: None,
+        }]
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_examples() {
+        use crate::test_examples;
+
+        test_examples(ScopeAliases {})
+    }
+}

crates/nu-cmd-lang/src/core_commands/scope/command.rs

@@ -0,0 +1,50 @@
+use nu_engine::get_full_help;
+use nu_protocol::{
+    ast::Call,
+    engine::{Command, EngineState, Stack},
+    Category, IntoPipelineData, PipelineData, ShellError, Signature, Type, Value,
+};
+
+#[derive(Clone)]
+pub struct Scope;
+
+impl Command for Scope {
+    fn name(&self) -> &str {
+        "scope"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("scope")
+            .category(Category::Core)
+            .input_output_types(vec![(Type::Nothing, Type::String)])
+            .allow_variants_without_examples(true)
+    }
+
+    fn usage(&self) -> &str {
+        "Commands for getting info about what is in scope."
+    }
+
+    fn is_parser_keyword(&self) -> bool {
+        true
+    }
+
+    fn run(
+        &self,
+        engine_state: &EngineState,
+        stack: &mut Stack,
+        call: &Call,
+        _input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        Ok(Value::String {
+            val: get_full_help(
+                &Scope.signature(),
+                &[],
+                engine_state,
+                stack,
+                self.is_parser_keyword(),
+            ),
+            span: call.head,
+        }
+        .into_pipeline_data())
+    }
+}

crates/nu-cmd-lang/src/core_commands/scope/commands.rs

@@ -0,0 +1,62 @@
+use nu_engine::scope::ScopeData;
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EngineState, Stack};
+use nu_protocol::{
+    Category, Example, IntoInterruptiblePipelineData, PipelineData, ShellError, Signature, Type,
+};
+
+#[derive(Clone)]
+pub struct ScopeCommands;
+
+impl Command for ScopeCommands {
+    fn name(&self) -> &str {
+        "scope commands"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("scope commands")
+            .input_output_types(vec![(Type::Nothing, Type::Any)])
+            .allow_variants_without_examples(true)
+            .category(Category::Filters)
+    }
+
+    fn usage(&self) -> &str {
+        "Output info on the commands in the current scope."
+    }
+
+    fn run(
+        &self,
+        engine_state: &EngineState,
+        stack: &mut Stack,
+        call: &Call,
+        _input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        let span = call.head;
+        let ctrlc = engine_state.ctrlc.clone();
+
+        let mut scope_data = ScopeData::new(engine_state, stack);
+        scope_data.populate_all();
+
+        Ok(scope_data.collect_commands(span).into_pipeline_data(ctrlc))
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            description: "Show the commands in the current scope",
+            example: "scope commands",
+            result: None,
+        }]
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_examples() {
+        use crate::test_examples;
+
+        test_examples(ScopeCommands {})
+    }
+}

crates/nu-cmd-lang/src/core_commands/scope/engine_stats.rs

@@ -0,0 +1,59 @@
+use nu_engine::scope::ScopeData;
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EngineState, Stack};
+use nu_protocol::{Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, Type};
+
+#[derive(Clone)]
+pub struct ScopeEngineStats;
+
+impl Command for ScopeEngineStats {
+    fn name(&self) -> &str {
+        "scope engine-stats"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("scope engine-stats")
+            .input_output_types(vec![(Type::Nothing, Type::Any)])
+            .allow_variants_without_examples(true)
+            .category(Category::Filters)
+    }
+
+    fn usage(&self) -> &str {
+        "Output stats on the engine in the current state."
+    }
+
+    fn run(
+        &self,
+        engine_state: &EngineState,
+        stack: &mut Stack,
+        call: &Call,
+        _input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        let span = call.head;
+
+        let mut scope_data = ScopeData::new(engine_state, stack);
+        scope_data.populate_all();
+
+        Ok(scope_data.collect_engine_state(span).into_pipeline_data())
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            description: "Show the stats on the current engine state",
+            example: "scope engine-stats",
+            result: None,
+        }]
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_examples() {
+        use crate::test_examples;
+
+        test_examples(ScopeEngineStats {})
+    }
+}

crates/nu-cmd-lang/src/core_commands/scope/mod.rs

@@ -0,0 +1,13 @@
+mod aliases;
+mod command;
+mod commands;
+mod engine_stats;
+mod modules;
+mod variables;
+
+pub use aliases::*;
+pub use command::*;
+pub use commands::*;
+pub use engine_stats::*;
+pub use modules::*;
+pub use variables::*;

crates/nu-cmd-lang/src/core_commands/scope/modules.rs

@@ -0,0 +1,62 @@
+use nu_engine::scope::ScopeData;
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EngineState, Stack};
+use nu_protocol::{
+    Category, Example, IntoInterruptiblePipelineData, PipelineData, ShellError, Signature, Type,
+};
+
+#[derive(Clone)]
+pub struct ScopeModules;
+
+impl Command for ScopeModules {
+    fn name(&self) -> &str {
+        "scope modules"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("scope modules")
+            .input_output_types(vec![(Type::Nothing, Type::Any)])
+            .allow_variants_without_examples(true)
+            .category(Category::Filters)
+    }
+
+    fn usage(&self) -> &str {
+        "Output info on the modules in the current scope."
+    }
+
+    fn run(
+        &self,
+        engine_state: &EngineState,
+        stack: &mut Stack,
+        call: &Call,
+        _input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        let span = call.head;
+        let ctrlc = engine_state.ctrlc.clone();
+
+        let mut scope_data = ScopeData::new(engine_state, stack);
+        scope_data.populate_modules();
+
+        Ok(scope_data.collect_modules(span).into_pipeline_data(ctrlc))
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            description: "Show the modules in the current scope",
+            example: "scope modules",
+            result: None,
+        }]
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_examples() {
+        use crate::test_examples;
+
+        test_examples(ScopeModules {})
+    }
+}

crates/nu-cmd-lang/src/core_commands/scope/variables.rs

@@ -0,0 +1,62 @@
+use nu_engine::scope::ScopeData;
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EngineState, Stack};
+use nu_protocol::{
+    Category, Example, IntoInterruptiblePipelineData, PipelineData, ShellError, Signature, Type,
+};
+
+#[derive(Clone)]
+pub struct ScopeVariables;
+
+impl Command for ScopeVariables {
+    fn name(&self) -> &str {
+        "scope variables"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("scope variables")
+            .input_output_types(vec![(Type::Nothing, Type::Any)])
+            .allow_variants_without_examples(true)
+            .category(Category::Filters)
+    }
+
+    fn usage(&self) -> &str {
+        "Output info on the variables in the current scope."
+    }
+
+    fn run(
+        &self,
+        engine_state: &EngineState,
+        stack: &mut Stack,
+        call: &Call,
+        _input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        let span = call.head;
+        let ctrlc = engine_state.ctrlc.clone();
+
+        let mut scope_data = ScopeData::new(engine_state, stack);
+        scope_data.populate_all();
+
+        Ok(scope_data.collect_vars(span).into_pipeline_data(ctrlc))
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            description: "Show the variables in the current scope",
+            example: "scope variables",
+            result: None,
+        }]
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_examples() {
+        use crate::test_examples;
+
+        test_examples(ScopeVariables {})
+    }
+}