From 75fedcc8dd082c22ca9077449cf4313342712b8f Mon Sep 17 00:00:00 2001
From: pwygab <88221256+merelymyself@users.noreply.github.com>
Date: Sat, 6 Apr 2024 22:03:05 +0800
Subject: [PATCH] prevent `select` (negative number) from hanging shell
 (#12393)
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# Description
Resolves #11756.
Resolves #12346.

As per description, shell no longer hangs:
```
~/CodingProjects/nushell> [1 2 3] | select (-2)
Error: nu::shell::cant_convert

  × Can't convert to cell path.
   ╭─[entry #1:1:18]
 1 │ [1 2 3] | select (-2)
   ·                  ──┬─
   ·                    ╰── can't convert negative number to cell path
   ╰────
```


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Added relevant test :rocket:

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Possibly support `get` `get`ting negative numbers, as per #12346
discussion. Alternatively, we can consider adding a cellpath for
negative indexing?
---
 crates/nu-command/src/filters/select.rs    | 10 +++++++++-
 crates/nu-command/tests/commands/select.rs |  6 ++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/crates/nu-command/src/filters/select.rs b/crates/nu-command/src/filters/select.rs
index dc9da1054c..916a4e8e5e 100644
--- a/crates/nu-command/src/filters/select.rs
+++ b/crates/nu-command/src/filters/select.rs
@@ -71,7 +71,15 @@ produce a table, a list will produce a list, and a record will produce a record.
                     };
                     new_columns.push(cv.clone());
                 }
-                Value::Int { val, .. } => {
+                Value::Int { val, internal_span } => {
+                    if val < 0 {
+                        return Err(ShellError::CantConvert {
+                            to_type: "cell path".into(),
+                            from_type: "negative number".into(),
+                            span: internal_span,
+                            help: None,
+                        });
+                    }
                     let cv = CellPath {
                         members: vec![PathMember::Int {
                             val: val as usize,
diff --git a/crates/nu-command/tests/commands/select.rs b/crates/nu-command/tests/commands/select.rs
index 7f2e9b8b57..028ecc3db7 100644
--- a/crates/nu-command/tests/commands/select.rs
+++ b/crates/nu-command/tests/commands/select.rs
@@ -275,3 +275,9 @@ fn select_single_row_with_variable() {
     assert_eq!(actual.out, "[[a]; [3]]".to_string());
     assert!(actual.err.is_empty());
 }
+
+#[test]
+fn select_with_negative_number_errors_out() {
+    let actual = nu!("[1 2 3] | select (-2)");
+    assert!(actual.err.contains("negative number"));
+}