Add a simple scope variable

crates/nu-command/src/default_context.rs

@@ -95,16 +95,6 @@ pub fn create_default_context() -> EngineState {
 
         let sig = Signature::build("exit");
         working_set.add_decl(sig.predeclare());
-        let sig = Signature::build("vars");
-        working_set.add_decl(sig.predeclare());
-        let sig = Signature::build("decls");
-        working_set.add_decl(sig.predeclare());
-        let sig = Signature::build("blocks");
-        working_set.add_decl(sig.predeclare());
-        let sig = Signature::build("stack");
-        working_set.add_decl(sig.predeclare());
-        let sig = Signature::build("contents");
-        working_set.add_decl(sig.predeclare());
 
         working_set.render()
     };

crates/nu-engine/src/eval.rs

@@ -371,12 +371,12 @@ pub fn eval_block(
 }
 
 pub fn eval_variable(
-    _engine_state: &EngineState,
+    engine_state: &EngineState,
     stack: &Stack,
     var_id: VarId,
     span: Span,
 ) -> Result<Value, ShellError> {
-    if var_id == 0 {
+    if var_id == nu_protocol::NU_VARIABLE_ID {
         // $nu
         let mut output_cols = vec![];
         let mut output_vals = vec![];
@@ -425,6 +425,71 @@ pub fn eval_variable(
             output_vals.push(Value::String { val: cwd, span })
         }
 
+        Ok(Value::Record {
+            cols: output_cols,
+            vals: output_vals,
+            span,
+        })
+    } else if var_id == nu_protocol::SCOPE_VARIABLE_ID {
+        let mut output_cols = vec![];
+        let mut output_vals = vec![];
+
+        let mut vars = vec![];
+        let mut commands = vec![];
+        let mut aliases = vec![];
+        let mut modules = vec![];
+
+        for frame in &engine_state.scope {
+            for var in &frame.vars {
+                vars.push(Value::String {
+                    val: String::from_utf8_lossy(var.0).to_string(),
+                    span,
+                });
+            }
+
+            for command in &frame.decls {
+                commands.push(Value::String {
+                    val: String::from_utf8_lossy(command.0).to_string(),
+                    span,
+                });
+            }
+
+            for alias in &frame.aliases {
+                aliases.push(Value::String {
+                    val: String::from_utf8_lossy(alias.0).to_string(),
+                    span,
+                });
+            }
+
+            for module in &frame.modules {
+                modules.push(Value::String {
+                    val: String::from_utf8_lossy(module.0).to_string(),
+                    span,
+                });
+            }
+        }
+
+        output_cols.push("vars".to_string());
+        output_vals.push(Value::List { vals: vars, span });
+
+        output_cols.push("commands".to_string());
+        output_vals.push(Value::List {
+            vals: commands,
+            span,
+        });
+
+        output_cols.push("aliases".to_string());
+        output_vals.push(Value::List {
+            vals: aliases,
+            span,
+        });
+
+        output_cols.push("modules".to_string());
+        output_vals.push(Value::List {
+            vals: modules,
+            span,
+        });
+
         Ok(Value::Record {
             cols: output_cols,
             vals: output_vals,

crates/nu-parser/src/parser.rs

@@ -1198,7 +1198,17 @@ pub fn parse_variable_expr(
     } else if contents == b"$nu" {
         return (
             Expression {
-                expr: Expr::Var(0),
+                expr: Expr::Var(nu_protocol::NU_VARIABLE_ID),
+                span,
+                ty: Type::Unknown,
+                custom_completion: None,
+            },
+            None,
+        );
+    } else if contents == b"$scope" {
+        return (
+            Expression {
+                expr: Expr::Var(nu_protocol::SCOPE_VARIABLE_ID),
                 span,
                 ty: Type::Unknown,
                 custom_completion: None,

crates/nu-protocol/src/engine/engine_state.rs

@@ -6,17 +6,6 @@ use std::{
     sync::{atomic::AtomicBool, Arc},
 };
 
-#[derive(Clone)]
-pub struct EngineState {
-    files: im::Vector<(String, usize, usize)>,
-    file_contents: im::Vector<(Vec<u8>, usize, usize)>,
-    vars: im::Vector<Type>,
-    decls: im::Vector<Box<dyn Command + 'static>>,
-    blocks: im::Vector<Block>,
-    pub scope: im::Vector<ScopeFrame>,
-    pub ctrlc: Option<Arc<AtomicBool>>,
-}
-
 // Tells whether a decl etc. is visible or not
 // TODO: When adding new exportables (env vars, aliases, etc.), parametrize the ID type with generics
 #[derive(Debug, Clone)]
@@ -62,9 +51,9 @@ impl Visibility {
 pub struct ScopeFrame {
     pub vars: HashMap<Vec<u8>, VarId>,
     predecls: HashMap<Vec<u8>, DeclId>, // temporary storage for predeclarations
-    decls: HashMap<Vec<u8>, DeclId>,
-    aliases: HashMap<Vec<u8>, Vec<Span>>,
-    modules: HashMap<Vec<u8>, BlockId>,
+    pub decls: HashMap<Vec<u8>, DeclId>,
+    pub aliases: HashMap<Vec<u8>, Vec<Span>>,
+    pub modules: HashMap<Vec<u8>, BlockId>,
     visibility: Visibility,
 }
 
@@ -91,18 +80,26 @@ impl Default for ScopeFrame {
     }
 }
 
-impl Default for EngineState {
-    fn default() -> Self {
-        Self::new()
-    }
+#[derive(Clone)]
+pub struct EngineState {
+    files: im::Vector<(String, usize, usize)>,
+    file_contents: im::Vector<(Vec<u8>, usize, usize)>,
+    vars: im::Vector<Type>,
+    decls: im::Vector<Box<dyn Command + 'static>>,
+    blocks: im::Vector<Block>,
+    pub scope: im::Vector<ScopeFrame>,
+    pub ctrlc: Option<Arc<AtomicBool>>,
 }
 
+pub const NU_VARIABLE_ID: usize = 0;
+pub const SCOPE_VARIABLE_ID: usize = 1;
+
 impl EngineState {
     pub fn new() -> Self {
         Self {
             files: im::vector![],
             file_contents: im::vector![],
-            vars: im::vector![Type::Unknown],
+            vars: im::vector![Type::Unknown, Type::Unknown],
             decls: im::vector![],
             blocks: im::vector![],
             scope: im::vector![ScopeFrame::new()],
@@ -319,6 +316,12 @@ impl EngineState {
     }
 }
 
+impl Default for EngineState {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 pub struct StateWorkingSet<'a> {
     pub permanent_state: &'a EngineState,
     pub delta: StateDelta,

crates/nu-protocol/src/lib.rs

@@ -11,6 +11,7 @@ mod ty;
 mod value;
 pub use value::Value;
 
+pub use engine::{NU_VARIABLE_ID, SCOPE_VARIABLE_ID};
 pub use example::*;
 pub use id::*;
 pub use pipeline_data::*;