Aliases (#1589)

* WIP getting scopes right

* finish adding initial support

* Finish with alias and add startup commands

crates/nu-protocol/src/return_value.rs

@@ -1,3 +1,4 @@
+use crate::hir::Commands;
 use crate::value::Value;
 use nu_errors::ShellError;
 use nu_source::{b, DebugDocBuilder, PrettyDebug};
@@ -20,6 +21,8 @@ pub enum CommandAction {
     EnterValueShell(Value),
     /// Enter the help shell, which allows exploring the help system
     EnterHelpShell(Value),
+    /// Enter the help shell, which allows exploring the help system
+    AddAlias(String, Vec<String>, Commands),
     /// Go to the previous shell in the shell ring buffer
     PreviousShell,
     /// Go to the next shell in the shell ring buffer
@@ -41,6 +44,7 @@ impl PrettyDebug for CommandAction {
             CommandAction::EnterShell(s) => b::typed("enter shell", b::description(s)),
             CommandAction::EnterValueShell(v) => b::typed("enter value shell", v.pretty()),
             CommandAction::EnterHelpShell(v) => b::typed("enter help shell", v.pretty()),
+            CommandAction::AddAlias(..) => b::description("add alias"),
             CommandAction::PreviousShell => b::description("previous shell"),
             CommandAction::NextShell => b::description("next shell"),
             CommandAction::LeaveShell => b::description("leave shell"),

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

@@ -1,11 +1,12 @@
 use crate::value::{Primitive, UntaggedValue, Value};
 use indexmap::IndexMap;
+use serde::{Deserialize, Serialize};
 use std::fmt::Debug;
 
 /// 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(Debug)]
+#[derive(Deserialize, Serialize, Debug, Clone)]
 pub struct Scope {
     pub it: Value,
     pub vars: IndexMap<String, Value>,
@@ -37,4 +38,20 @@ impl Scope {
             vars: IndexMap::new(),
         }
     }
+
+    pub fn set_it(self, value: Value) -> Scope {
+        Scope {
+            it: value,
+            vars: self.vars,
+        }
+    }
+
+    pub fn set_var(self, name: String, value: Value) -> Scope {
+        let mut new_vars = self.vars.clone();
+        new_vars.insert(name, value);
+        Scope {
+            it: self.it,
+            vars: new_vars,
+        }
+    }
 }