Negative indexing for range (#3427)

* adds negative indexing to range

* fixes tests to reflect new parsing changes

* removes duplicate definitons

* fmt

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

@@ -1,7 +1,7 @@
 use crate::prelude::*;
 use nu_engine::WholeStreamCommand;
 use nu_errors::ShellError;
-use nu_protocol::{Signature, SyntaxShape, Value};
+use nu_protocol::{Signature, SyntaxShape, UntaggedValue, Value};
 
 struct RangeArgs {
     range: nu_protocol::Range,
@@ -26,6 +26,29 @@ impl WholeStreamCommand for Range {
         "Return only the selected rows."
     }
 
+    fn examples(&self) -> Vec<Example> {
+        vec![
+            Example {
+                description: "Return rows 1 through 3",
+                example: "echo [1 2 3 4 5] | range 1..3",
+                result: Some(vec![
+                    UntaggedValue::int(2).into(),
+                    UntaggedValue::int(3).into(),
+                    UntaggedValue::int(4).into(),
+                ]),
+            },
+            Example {
+                description: "Return the third row from the end, through to the end",
+                example: "echo [1 2 3 4 5] | range (-3..)",
+                result: Some(vec![
+                    UntaggedValue::int(3).into(),
+                    UntaggedValue::int(4).into(),
+                    UntaggedValue::int(5).into(),
+                ]),
+            },
+        ]
+    }
+
     fn run(&self, args: CommandArgs) -> Result<OutputStream, ShellError> {
         range(args)
     }
@@ -37,13 +60,40 @@ fn range(args: CommandArgs) -> Result<OutputStream, ShellError> {
         range: args.req(0)?,
     };
 
-    let from = cmd_args.range.min_usize()?;
+    let from_raw = cmd_args.range.min_i64()?;
-    let to = cmd_args.range.max_usize()?;
+    let to_raw = cmd_args.range.max_i64()?;
+    // only collect the input if we have any negative indices
+    if from_raw < 0 || to_raw < 0 {
+        let input = args.input.into_vec();
+        let input_size = input.len() as i64;
 
-    if from > to {
+        let from = if from_raw < 0 {
-        Ok(OutputStream::one(Value::nothing()))
+            (input_size + from_raw) as usize
+        } else {
+            from_raw as usize
+        };
+
+        let to = if to_raw < 0 {
+            (input_size + to_raw) as usize
+        } else if to_raw > input.len() as i64 {
+            input.len()
+        } else {
+            to_raw as usize
+        };
+
+        if from > to {
+            Ok(OutputStream::one(Value::nothing()))
+        } else {
+            Ok(OutputStream::from(input[from..to].to_vec()))
+        }
     } else {
-        Ok(args.input.skip(from).take(to - from + 1).to_output_stream())
+        let from = from_raw as usize;
+        let to = to_raw as usize;
+        if from > to {
+            Ok(OutputStream::one(Value::nothing()))
+        } else {
+            Ok(args.input.skip(from).take(to - from + 1).to_output_stream())
+        }
     }
 }
 

crates/nu-command/tests/commands/range.rs

@@ -43,3 +43,26 @@ fn selects_some_rows() {
         assert_eq!(actual.out, "2");
     });
 }
+
+#[test]
+fn negative_indices() {
+    Playground::setup("range_test_negative_indices", |dirs, sandbox| {
+        sandbox.with_files(vec![
+            EmptyFile("notes.txt"),
+            EmptyFile("tests.txt"),
+            EmptyFile("persons.txt"),
+        ]);
+
+        let actual = nu!(
+            cwd: dirs.test(), pipeline(
+            r#"
+                ls
+                | get name
+                | range (-1..)
+                | length
+            "#
+        ));
+
+        assert_eq!(actual.out, "1");
+    });
+}