Improve alias highlighting/completions (#3594)

* Improve alias highlighting/completions

* Add example

crates/nu-command/src/commands.rs

@@ -4,6 +4,7 @@ pub(crate) mod macros;
 mod from_delimited_data;
 mod to_delimited_data;
 
+pub(crate) mod alias;
 pub(crate) mod all;
 pub(crate) mod ansi;
 pub(crate) mod any;
@@ -145,6 +146,7 @@ pub(crate) mod wrap;
 pub(crate) use autoview::Autoview;
 pub(crate) use cd::Cd;
 
+pub(crate) use alias::Alias;
 pub(crate) use ansi::Ansi;
 pub(crate) use ansi::AnsiGradient;
 pub(crate) use ansi::AnsiStrip;

crates/nu-command/src/commands/alias.rs

@@ -0,0 +1,40 @@
+use crate::prelude::*;
+use nu_engine::WholeStreamCommand;
+
+use nu_errors::ShellError;
+use nu_protocol::{Signature, SyntaxShape};
+
+pub struct Alias;
+
+impl WholeStreamCommand for Alias {
+    fn name(&self) -> &str {
+        "alias"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("alias")
+            .required("name", SyntaxShape::String, "the name of the alias")
+            .required("equals", SyntaxShape::String, "the equals sign")
+            .rest(SyntaxShape::Any, "the expansion for the alias")
+    }
+
+    fn usage(&self) -> &str {
+        "Alias a command to an expansion."
+    }
+
+    fn run(&self, args: CommandArgs) -> Result<OutputStream, ShellError> {
+        alias(args)
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            description: "Alias ll to ls -l",
+            example: "alias ll = ls -l",
+            result: None,
+        }]
+    }
+}
+
+pub fn alias(_: CommandArgs) -> Result<OutputStream, ShellError> {
+    Ok(OutputStream::empty())
+}

crates/nu-command/src/commands/default_context.rs

@@ -16,6 +16,7 @@ pub fn create_default_context(interactive: bool) -> Result<EvaluationContext, Bo
             whole_stream_command(LoadEnv),
             whole_stream_command(Def),
             whole_stream_command(Source),
+            whole_stream_command(Alias),
             // System/file operations
             whole_stream_command(Exec),
             whole_stream_command(Pwd),

crates/nu-parser/src/parse.rs

@@ -1826,16 +1826,6 @@ fn parse_call(
         let (_, expr, err) = parse_math_expression(0, &lite_cmd.parts[..], scope, false);
         error = error.or(err);
         return (Some(ClassifiedCommand::Expr(Box::new(expr))), error);
-    } else if lite_cmd.parts[0].item == "alias" {
-        let error = parse_alias(&lite_cmd, scope);
-        if error.is_none() {
-            return (None, None);
-        } else {
-            return (
-                Some(ClassifiedCommand::Expr(Box::new(garbage(lite_cmd.span())))),
-                error,
-            );
-        }
     } else if lite_cmd.parts.len() > 1 {
         // Check if it's a sub-command
         if let Some(signature) = scope.get_signature(&format!(
@@ -1899,6 +1889,13 @@ fn parse_call(
                     )),
                 );
             }
+        } else if lite_cmd.parts[0].item == "alias" {
+            let error = parse_alias(&lite_cmd, scope);
+            if error.is_none() {
+                return (Some(ClassifiedCommand::Internal(internal_command)), None);
+            } else {
+                return (Some(ClassifiedCommand::Internal(internal_command)), error);
+            }
         }
 
         error = error.or(err);