allow select to stream more (#14492)

# Description

closes https://github.com/nushell/nushell/issues/14487

This PR tries to allow the `select` to stream better by changing the for
loops that collected the output into a `Vec<Value>` prior to returning
it into a map that returns the data as it is processed.

One curiosity, `select` transforms the input into a `PipelineIterator`.
If I remove this code, it still passes all tests. I'm not sure all this
`PipelineIterator` code is even needed. I left it for someone to tell me
if it's necessary.

# User-Facing Changes
<!-- List of all changes that impact the user experience here. This
helps us keep track of breaking changes. -->

# 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` to
check that you're using the standard code style
- `cargo test --workspace` to check that all tests pass (on Windows make
sure to [enable developer
mode](https://learn.microsoft.com/en-us/windows/apps/get-started/developer-mode-features-and-debugging))
- `cargo run -- -c "use toolkit.nu; toolkit test stdlib"` to run the
tests for the standard library

> **Note**
> from `nushell` you can also use the `toolkit` as follows
> ```bash
> use toolkit.nu # or use an `env_change` hook to activate it
automatically
> toolkit check pr
> ```
-->

# 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/filters/select.rs

@@ -206,7 +206,6 @@ fn select(
     let columns = new_columns;
 
     let input = if !unique_rows.is_empty() {
-        // let skip = call.has_flag(engine_state, stack, "skip")?;
         let metadata = input.metadata();
         let pipeline_iter: PipelineIterator = input.into_iter();
 
@@ -231,9 +230,9 @@ fn select(
                 Value::List {
                     vals: input_vals, ..
                 } => {
-                    let mut output = vec![];
+                    Ok(input_vals
-                    let mut columns_with_value = Vec::new();
+                        .into_iter()
-                    for input_val in input_vals {
+                        .map(move |input_val| {
                             if !columns.is_empty() {
                                 let mut record = Record::new();
                                 for path in &columns {
@@ -241,23 +240,17 @@ fn select(
                                     match input_val.clone().follow_cell_path(&path.members, false) {
                                         Ok(fetcher) => {
                                             record.push(path.to_column_name(), fetcher);
-                                        if !columns_with_value.contains(&path) {
-                                            columns_with_value.push(path);
-                                        }
-                                    }
-                                    Err(e) => {
-                                        return Err(e);
                                         }
+                                        Err(e) => return Value::error(e, call_span),
                                     }
                                 }
 
-                            output.push(Value::record(record, span))
+                                Value::record(record, span)
                             } else {
-                            output.push(input_val)
+                                input_val.clone()
                             }
-                    }
+                        })
-
+                        .into_pipeline_data_with_metadata(
-                    Ok(output.into_iter().into_pipeline_data_with_metadata(
                             call_span,
                             engine_state.signals().clone(),
                             metadata,
@@ -286,9 +279,8 @@ fn select(
             }
         }
         PipelineData::ListStream(stream, metadata, ..) => {
-            let mut values = vec![];
+            Ok(stream
-
+                .map(move |x| {
-            for x in stream {
                     if !columns.is_empty() {
                         let mut record = Record::new();
                         for path in &columns {
@@ -297,16 +289,15 @@ fn select(
                                 Ok(value) => {
                                     record.push(path.to_column_name(), value);
                                 }
-                            Err(e) => return Err(e),
+                                Err(e) => return Value::error(e, call_span),
                             }
                         }
-                    values.push(Value::record(record, call_span));
+                        Value::record(record, call_span)
                     } else {
-                    values.push(x);
+                        x
                     }
-            }
+                })
-
+                .into_pipeline_data_with_metadata(
-            Ok(values.into_pipeline_data_with_metadata(
                     call_span,
                     engine_state.signals().clone(),
                     metadata,

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

@@ -63,7 +63,7 @@ fn complex_nested_columns() {
 fn fails_if_given_unknown_column_name() {
     let actual = nu!(pipeline(
         r#"
-            echo [
+            [
                 [first_name, last_name, rusty_at, type];
 
                 [Andrés Robalino '10/11/2013' A]
@@ -71,7 +71,6 @@ fn fails_if_given_unknown_column_name() {
                 [Yehuda Katz '10/11/2013' A]
             ]
             | select rrusty_at first_name
-            | length
         "#
     ));