Refactor scope (#2602)

* Refactor scope to have parents

* Refactor scope to have parents

* Refactor scope to have parents

* Clippy

Co-authored-by: Jonathan Turner <jonathan@pop-os.localdomain>

crates/nu-protocol/src/value/evaluate.rs

@@ -2,30 +2,121 @@ use crate::value::Value;
 use indexmap::IndexMap;
 use serde::{Deserialize, Serialize};
 use std::fmt::Debug;
+use std::sync::Arc;
 
 /// An evaluation scope. Scopes map variable names to Values and aid in evaluating blocks and expressions.
 /// Additionally, holds the value for the special $it variable, a variable used to refer to the value passing
 /// through the pipeline at that moment
 #[derive(Deserialize, Serialize, Debug, Clone)]
 pub struct Scope {
-    pub it: Value,
-    pub vars: IndexMap<String, Value>,
-    pub env: IndexMap<String, String>,
+    vars: IndexMap<String, Value>,
+    env: IndexMap<String, String>,
+    parent: Option<Arc<Scope>>,
 }
 
 impl Scope {
-    /// Create an empty scope
-    pub fn new() -> Scope {
-        Scope {
-            it: Value::nothing(),
-            vars: IndexMap::new(),
-            env: IndexMap::new(),
+    pub fn vars(&self) -> IndexMap<String, Value> {
+        //FIXME: should this be an interator?
+
+        let mut output = IndexMap::new();
+
+        for v in &self.vars {
+            output.insert(v.0.clone(), v.1.clone());
+        }
+
+        if let Some(parent) = &self.parent {
+            for v in parent.vars() {
+                if !output.contains_key(&v.0) {
+                    output.insert(v.0.clone(), v.1.clone());
+                }
+            }
+        }
+
+        output
+    }
+
+    pub fn env(&self) -> IndexMap<String, String> {
+        //FIXME: should this be an interator?
+
+        let mut output = IndexMap::new();
+
+        for v in &self.env {
+            output.insert(v.0.clone(), v.1.clone());
+        }
+
+        if let Some(parent) = &self.parent {
+            for v in parent.env() {
+                if !output.contains_key(&v.0) {
+                    output.insert(v.0.clone(), v.1.clone());
+                }
+            }
+        }
+
+        output
+    }
+
+    pub fn var(&self, name: &str) -> Option<Value> {
+        if let Some(value) = self.vars().get(name) {
+            Some(value.clone())
+        } else {
+            None
         }
     }
-}
 
-impl Default for Scope {
-    fn default() -> Scope {
-        Scope::new()
+    pub fn it(&self) -> Option<Value> {
+        self.var("$it")
+    }
+
+    pub fn from_env(env: IndexMap<String, String>) -> Arc<Scope> {
+        Arc::new(Scope {
+            vars: IndexMap::new(),
+            env,
+            parent: None,
+        })
+    }
+
+    pub fn append_it(this: Arc<Self>, it: Value) -> Arc<Scope> {
+        let mut vars = IndexMap::new();
+        vars.insert("$it".into(), it);
+        Arc::new(Scope {
+            vars,
+            env: IndexMap::new(),
+            parent: Some(this),
+        })
+    }
+
+    pub fn append_var(this: Arc<Self>, name: String, value: Value) -> Arc<Scope> {
+        let mut vars = IndexMap::new();
+        vars.insert(name, value);
+        Arc::new(Scope {
+            vars,
+            env: IndexMap::new(),
+            parent: Some(this),
+        })
+    }
+
+    pub fn append_vars(this: Arc<Self>, vars: IndexMap<String, Value>) -> Arc<Scope> {
+        Arc::new(Scope {
+            vars,
+            env: IndexMap::new(),
+            parent: Some(this),
+        })
+    }
+
+    pub fn append_env(this: Arc<Self>, env: IndexMap<String, String>) -> Arc<Scope> {
+        Arc::new(Scope {
+            vars: IndexMap::new(),
+            env,
+            parent: Some(this),
+        })
+    }
+
+    /// Create an empty scope
+    pub fn create() -> Arc<Scope> {
+        Arc::new(Scope {
+            vars: IndexMap::new(),
+            env: IndexMap::new(),
+            parent: None,
+        })
     }
 }