From 7fcebf37ececb98b96e478304138ef920a64507a Mon Sep 17 00:00:00 2001
From: Julian Amarilla <julian.amarilla995@gmail.com>
Date: Thu, 17 Apr 2025 11:57:25 -0300
Subject: [PATCH] Fix #15440 default --empty fails at empty streams (#15562)

Fixes #15440

# Description
Wraps ListStream stream type from `impl Iterator` to `Peekable<impl
Iterator>`, this allows checking for empty streams and treating them as
empty values

Example:
```
# previously
$ glob ? | default -e void
> # empty list

$ echo '' | default -e void
> void

####################

# now
$ glob ? | default -e void
> void

$ echo '' | default -e void
> void
```

# User-Facing Changes

empty list streams will behave as `nothing` values when testing for
emptiness

# Tests + Formatting

- Add 2 tests
- clippy OK
- fmt OK

# After Submitting
---
 crates/nu-command/src/filters/default.rs    | 15 ++++++++
 crates/nu-command/tests/commands/default.rs | 40 ++++++++++++++++++++-
 2 files changed, 54 insertions(+), 1 deletion(-)

diff --git a/crates/nu-command/src/filters/default.rs b/crates/nu-command/src/filters/default.rs
index c9a1506d4b..f0dc641d5f 100644
--- a/crates/nu-command/src/filters/default.rs
+++ b/crates/nu-command/src/filters/default.rs
@@ -1,4 +1,5 @@
 use nu_engine::command_prelude::*;
+use nu_protocol::{ListStream, Signals};
 
 #[derive(Clone)]
 pub struct Default;
@@ -146,6 +147,20 @@ fn default(
             && matches!(input, PipelineData::Value(ref value, _) if value.is_empty()))
     {
         Ok(value.into_pipeline_data())
+    } else if default_when_empty && matches!(input, PipelineData::ListStream(..)) {
+        let PipelineData::ListStream(ls, metadata) = input else {
+            unreachable!()
+        };
+        let span = ls.span();
+        let mut stream = ls.into_inner().peekable();
+        if stream.peek().is_none() {
+            return Ok(value.into_pipeline_data());
+        }
+
+        // stream's internal state already preserves the original signals config, so if this
+        // Signals::empty list stream gets interrupted it will be caught by the underlying iterator
+        let ls = ListStream::new(stream, span, Signals::empty());
+        Ok(PipelineData::ListStream(ls, metadata))
     } else {
         Ok(input)
     }
diff --git a/crates/nu-command/tests/commands/default.rs b/crates/nu-command/tests/commands/default.rs
index 1669aea4d1..b17e334b12 100644
--- a/crates/nu-command/tests/commands/default.rs
+++ b/crates/nu-command/tests/commands/default.rs
@@ -1,4 +1,4 @@
-use nu_test_support::{nu, pipeline};
+use nu_test_support::{fs::Stub::EmptyFile, nu, pipeline, playground::Playground};
 
 #[test]
 fn adds_row_data_if_column_missing() {
@@ -112,3 +112,41 @@ fn do_not_replace_empty_record() {
     let actual = nu!(r#"{} | default {a:5} | columns | length"#);
     assert_eq!(actual.out, "0");
 }
+
+#[test]
+fn replace_empty_list_stream() {
+    // This is specific for testing ListStreams when empty behave like other empty values
+    Playground::setup("glob_empty_list", |dirs, sandbox| {
+        sandbox.with_files(&[
+            EmptyFile("yehuda.txt"),
+            EmptyFile("jttxt"),
+            EmptyFile("andres.txt"),
+        ]);
+
+        let actual = nu!(
+            cwd: dirs.test(),
+            "glob ? | default -e void",
+        );
+
+        assert_eq!(actual.out, "void");
+    })
+}
+
+#[test]
+fn do_not_replace_non_empty_list_stream() {
+    // This is specific for testing ListStreams when empty behave like other empty values
+    Playground::setup("glob_non_empty_list", |dirs, sandbox| {
+        sandbox.with_files(&[
+            EmptyFile("yehuda.txt"),
+            EmptyFile("jt.rs"),
+            EmptyFile("andres.txt"),
+        ]);
+
+        let actual = nu!(
+            cwd: dirs.test(),
+            "glob '*.txt' | default -e void | length",
+        );
+
+        assert_eq!(actual.out, "2");
+    })
+}