make save stream on list stream data (#7675)

# Description

Closes: #7590

# User-Facing Changes

So the following command
```
1..100 | each { |i| sleep 400ms; $i} | save --raw -f output.txt
```

Will stream data to `output.txt`

But I'm note sure how to make a proper test for it, so I leave with no
new test cases..

Also rename from `string_binary_list_value_to_bytes ` to
`value_to_bytes` to accepts more Value type.

# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

crates/nu-command/src/filesystem/save.rs

@@ -108,6 +108,20 @@ impl Command for Save {
                     res
                 }
             }
+            PipelineData::ListStream(ls, _)
+                if raw || prepare_path(&path, append, force)?.0.extension().is_none() =>
+            {
+                let (mut file, _) = get_files(&path, &stderr_path, append, force)?;
+                for val in ls {
+                    file.write_all(&value_to_bytes(val)?)
+                        .map_err(|err| ShellError::IOError(err.to_string()))?;
+                    file.write_all("\n".as_bytes())
+                        .map_err(|err| ShellError::IOError(err.to_string()))?;
+                }
+                file.flush()?;
+
+                Ok(PipelineData::empty())
+            }
             input => {
                 let bytes =
                     input_to_bytes(input, Path::new(&path.item), raw, engine_state, stack, span)?;
@@ -182,7 +196,7 @@ fn input_to_bytes(
         convert_to_extension(engine_state, &ext, stack, input, span)
     } else {
         let value = input.into_value(span);
-        string_binary_list_value_to_bytes(value, span)
+        value_to_bytes(value)
     }
 }
 
@@ -212,13 +226,13 @@ fn convert_to_extension(
         None => input.into_value(span),
     };
 
-    string_binary_list_value_to_bytes(output, span)
+    value_to_bytes(output)
 }
 
 /// Convert [`Value::String`] [`Value::Binary`] or [`Value::List`] into [`Vec`] of bytes
 ///
 /// Propagates [`Value::Error`] and creates error otherwise
-fn string_binary_list_value_to_bytes(value: Value, span: Span) -> Result<Vec<u8>, ShellError> {
+fn value_to_bytes(value: Value) -> Result<Vec<u8>, ShellError> {
     match value {
         Value::String { val, .. } => Ok(val.into_bytes()),
         Value::Binary { val, .. } => Ok(val),
@@ -234,13 +248,7 @@ fn string_binary_list_value_to_bytes(value: Value, span: Span) -> Result<Vec<u8>
         }
         // Propagate errors by explicitly matching them before the final case.
         Value::Error { error } => Err(error),
-        other => Err(ShellError::OnlySupportsThisInputType(
-            "string, binary or list".into(),
-            other.get_type().to_string(),
-            span,
-            // This line requires the Value::Error match above.
-            other.expect_span(),
-        )),
+        other => Ok(other.as_string()?.into_bytes()),
     }
 }
 

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

@@ -264,3 +264,20 @@ fn save_override_works_stderr() {
         assert_eq!(actual, "New Err\n");
     })
 }
+
+#[test]
+fn save_list_stream() {
+    Playground::setup("save_test_13", |dirs, sandbox| {
+        sandbox.with_files(vec![]);
+
+        let expected_file = dirs.test().join("list_sample.txt");
+
+        nu!(
+            cwd: dirs.root(),
+            r#"[a b c d] | each {|i| $i} | save -r save_test_13/list_sample.txt"#,
+        );
+
+        let actual = file_contents(expected_file);
+        assert_eq!(actual, "a\nb\nc\nd\n")
+    })
+}