Add the ability to remove and list aliases (#3879)

* Add the ability to remove and list aliases

* Fix failing unit tests

* Add a test to check unalias shadowing blocks

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

@@ -2,7 +2,7 @@ use crate::prelude::*;
 use nu_engine::WholeStreamCommand;
 
 use nu_errors::ShellError;
-use nu_protocol::{Signature, SyntaxShape};
+use nu_protocol::{Signature, SyntaxShape, UntaggedValue};
 
 pub struct Alias;
 
@@ -35,6 +35,18 @@ impl WholeStreamCommand for Alias {
     }
 }
 
-pub fn alias(_: CommandArgs) -> Result<OutputStream, ShellError> {
+pub fn alias(args: CommandArgs) -> Result<OutputStream, ShellError> {
+    // TODO: is there a better way of checking whether no arguments were passed?
+    if args.nth(0).is_none() {
+        let aliases = UntaggedValue::string(
+            &args
+                .scope()
+                .get_aliases()
+                .iter()
+                .map(|val| format!("{} = '{}'", val.0, val.1.iter().map(|x| &x.item).join(" ")))
+                .join("\n"),
+        );
+        return Ok(OutputStream::one(aliases));
+    }
     Ok(OutputStream::empty())
 }

crates/nu-command/src/commands/core_commands/mod.rs

@@ -13,6 +13,7 @@ mod nu_plugin;
 mod nu_signature;
 mod source;
 mod tags;
+mod unalias;
 mod version;
 
 pub use self::nu_plugin::SubCommand as NuPlugin;
@@ -32,4 +33,5 @@ pub use ignore::Ignore;
 pub use let_::Let;
 pub use source::Source;
 pub use tags::Tags;
+pub use unalias::Unalias;
 pub use version::{version, Version};

crates/nu-command/src/commands/core_commands/unalias.rs

@@ -0,0 +1,37 @@
+use crate::prelude::*;
+use nu_engine::WholeStreamCommand;
+
+use nu_errors::ShellError;
+use nu_protocol::{Signature, SyntaxShape};
+
+pub struct Unalias;
+
+impl WholeStreamCommand for Unalias {
+    fn name(&self) -> &str {
+        "unalias"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("unalias").required("name", SyntaxShape::String, "the name of the alias")
+    }
+
+    fn usage(&self) -> &str {
+        "Removes an alias"
+    }
+
+    fn run(&self, args: CommandArgs) -> Result<OutputStream, ShellError> {
+        unalias(args)
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            description: "Remove the 'v' alias",
+            example: "unalias v",
+            result: None,
+        }]
+    }
+}
+
+pub fn unalias(_: CommandArgs) -> Result<OutputStream, ShellError> {
+    Ok(OutputStream::empty())
+}

crates/nu-command/src/default_context.rs

@@ -18,6 +18,7 @@ pub fn create_default_context(interactive: bool) -> Result<EvaluationContext, Bo
             whole_stream_command(Def),
             whole_stream_command(Source),
             whole_stream_command(Alias),
+            whole_stream_command(Unalias),
             whole_stream_command(Ignore),
             // System/file operations
             whole_stream_command(Exec),

crates/nu-completion/src/engine.rs

@@ -317,6 +317,10 @@ mod tests {
             todo!()
         }
 
+        fn remove_alias(&self, _name: &str) {
+            todo!()
+        }
+
         fn add_definition(&self, _block: Arc<Block>) {}
 
         fn get_definitions(&self) -> Vec<Arc<Block>> {

crates/nu-engine/src/evaluate/scope.rs

@@ -407,6 +407,12 @@ impl ParserScope for Scope {
         }
     }
 
+    fn remove_alias(&self, name: &str) {
+        for frame in self.frames.lock().iter_mut().rev() {
+            frame.aliases.remove(name);
+        }
+    }
+
     fn enter_scope(&self) {
         self.frames.lock().push(ScopeFrame::new());
     }

crates/nu-parser/src/parse.rs

@@ -1902,7 +1902,7 @@ fn parse_call(
                     )),
                 );
             }
-        } else if lite_cmd.parts[0].item == "alias" {
+        } else if lite_cmd.parts[0].item == "alias" || lite_cmd.parts[0].item == "unalias" {
             let error = parse_alias(&lite_cmd, scope);
             if error.is_none() {
                 return (Some(ClassifiedCommand::Internal(internal_command)), None);
@@ -2048,26 +2048,41 @@ fn expand_shorthand_forms(
 }
 
 fn parse_alias(call: &LiteCommand, scope: &dyn ParserScope) -> Option<ParseError> {
-    if call.parts.len() == 2 && (call.parts[1].item == "--help" || (call.parts[1].item == "-h")) {
-        return None;
-    }
+    if call.parts[0].item == "alias" {
+        if (call.parts.len() == 1)
+            || (call.parts.len() == 2
+                && (call.parts[1].item == "--help" || (call.parts[1].item == "-h")))
+        {
+            return None;
+        }
+        if call.parts.len() < 4 {
+            return Some(ParseError::mismatch("alias", call.parts[0].clone()));
+        }
 
-    if call.parts.len() < 4 {
-        return Some(ParseError::mismatch("alias", call.parts[0].clone()));
-    }
+        if call.parts[0].item != "alias" {
+            return Some(ParseError::mismatch("alias", call.parts[0].clone()));
+        }
 
-    if call.parts[0].item != "alias" {
-        return Some(ParseError::mismatch("alias", call.parts[0].clone()));
-    }
-
-    if call.parts[2].item != "=" {
-        return Some(ParseError::mismatch("=", call.parts[2].clone()));
+        if call.parts[2].item != "=" {
+            return Some(ParseError::mismatch("=", call.parts[2].clone()));
+        }
+    } else {
+        // unalias
+        if call.parts.len() != 2 {
+            return Some(ParseError::mismatch("unalias", call.parts[0].clone()));
+        }
     }
 
     let name = call.parts[1].item.clone();
     let args: Vec<_> = call.parts.iter().skip(3).cloned().collect();
 
-    scope.add_alias(&name, args);
+    match call.parts[0].item.as_str() {
+        "alias" => scope.add_alias(&name, args),
+        "unalias" => {
+            scope.remove_alias(&name);
+        }
+        _ => unreachable!(),
+    };
 
     None
 }

crates/nu-parser/src/scope.rs

@@ -13,6 +13,8 @@ pub trait ParserScope: Debug {
 
     fn get_alias(&self, name: &str) -> Option<Vec<Spanned<String>>>;
 
+    fn remove_alias(&self, name: &str);
+
     fn add_alias(&self, name: &str, replacement: Vec<Spanned<String>>);
 
     fn enter_scope(&self);

tests/shell/pipeline/commands/internal.rs

@@ -1145,6 +1145,21 @@ fn nothing_string_2() {
     assert_eq!(actual.out, "true");
 }
 
+#[test]
+fn unalias_shadowing() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+        alias ll = ls -l
+        let xyz = { ll -a }
+        unalias ll
+        do $xyz
+        "#)
+    );
+
+    assert_eq!(actual.out, "");
+}
+
 mod parse {
     use nu_test_support::nu;