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())
+}