Remove some unnecessary static Vecs (#11947)

Avoid unnecessary allocations or larger iterator structs

- Turn static `Vec`s into arrays when possible
- Use `std::iter::once`/`empty` where applicable
- Use `bool::then_some` in `detect column` `.chain`
- Drop in the bucket: de-vec-ing tests

crates/nu-cli/src/completions/command_completions.rs

@@ -253,7 +253,7 @@ mod command_completions_tests {
 
     #[test]
     fn test_find_non_whitespace_index() {
-        let commands = vec![
+        let commands = [
             ("    hello", 4),
             ("sudo ", 0),
             (" 	sudo ", 2),
@@ -273,7 +273,7 @@ mod command_completions_tests {
 
     #[test]
     fn test_is_last_command_passthrough() {
-        let commands = vec![
+        let commands = [
             ("    hello", false),
             ("    sudo ", true),
             ("sudo ", true),

crates/nu-cli/src/completions/completer.rs

@@ -564,7 +564,7 @@ mod completer_tests {
         );
 
         let mut completer = NuCompleter::new(engine_state.into(), Stack::new());
-        let dataset = vec![
+        let dataset = [
             ("sudo", false, "", Vec::new()),
             ("sudo l", true, "l", vec!["ls", "let", "lines", "loop"]),
             (" sudo", false, "", Vec::new()),

crates/nu-cli/src/reedline_config.rs

@@ -84,7 +84,7 @@ pub(crate) fn add_menus(
     }
 
     // Checking if the default menus have been added from the config file
-    let default_menus = vec![
+    let default_menus = [
         ("completion_menu", DEFAULT_COMPLETION_MENU),
         ("history_menu", DEFAULT_HISTORY_MENU),
         ("help_menu", DEFAULT_HELP_MENU),

crates/nu-cmd-lang/src/core_commands/do_.rs

@@ -154,9 +154,9 @@ impl Command for Do {
                             let ctrlc = stdout_stream.ctrlc.clone();
                             let span = stdout_stream.span;
                             RawStream::new(
-                                Box::new(
-                                    vec![stdout_stream.into_bytes().map(|s| s.item)].into_iter(),
-                                ),
+                                Box::new(std::iter::once(
+                                    stdout_stream.into_bytes().map(|s| s.item),
+                                )),
                                 ctrlc,
                                 span,
                                 None,
@@ -213,7 +213,7 @@ impl Command for Do {
                 Ok(PipelineData::ExternalStream {
                     stdout,
                     stderr: Some(RawStream::new(
-                        Box::new(vec![Ok(stderr_msg.into_bytes())].into_iter()),
+                        Box::new(std::iter::once(Ok(stderr_msg.into_bytes()))),
                         stderr_ctrlc,
                         span,
                         None,

crates/nu-command/src/date/utils.rs

@@ -46,7 +46,7 @@ pub(crate) fn generate_strftime_list(head: Span, show_parse_only_formats: bool)
         description: &'a str,
     }
 
-    let specifications = vec![
+    let specifications = [
         FormatSpecification {
             spec: "%Y",
             description: "The full proleptic Gregorian year, zero-padded to 4 digits.",

crates/nu-command/src/filters/get.rs

@@ -85,7 +85,7 @@ If multiple cell paths are given, this will produce a list of values."#
         } else {
             let mut output = vec![];
 
-            let paths = vec![cell_path].into_iter().chain(rest);
+            let paths = std::iter::once(cell_path).chain(rest);
 
             let input = input.into_value(span);
 

crates/nu-command/src/strings/detect_columns.rs

@@ -128,11 +128,10 @@ fn detect_columns(
             }
         }
 
-        Ok((if noheader {
-            vec![orig_headers].into_iter().chain(input)
-        } else {
-            vec![].into_iter().chain(input)
-        })
+        Ok(noheader
+            .then_some(orig_headers)
+            .into_iter()
+            .chain(input)
             .map(move |x| {
                 let row = find_columns(&x);
 
@@ -148,7 +147,9 @@ fn detect_columns(
                     // column counts don't line up, so see if we can figure out why
                     for cell in row {
                         for header in &headers {
-                        if cell.span.start <= header.span.end && cell.span.end > header.span.start {
+                            if cell.span.start <= header.span.end
+                                && cell.span.end > header.span.start
+                            {
                                 pre_output.push((
                                     header.item.to_string(),
                                     Value::string(&cell.item, name_span),
@@ -195,7 +196,8 @@ fn detect_columns(
                                 r_idx
                             };
 
-                        if !(l_idx <= r_idx && (r_idx >= 0 || l_idx < (record.len() as isize))) {
+                            if !(l_idx <= r_idx && (r_idx >= 0 || l_idx < (record.len() as isize)))
+                            {
                                 return Value::record(record, name_span);
                             }
 

crates/nu-engine/src/eval.rs

@@ -550,7 +550,7 @@ fn eval_element_with_input(
                                     // so nushell knows this result is not the last part of a command.
                                     (
                                         Some(RawStream::new(
-                                            Box::new(vec![].into_iter()),
+                                            Box::new(std::iter::empty()),
                                             None,
                                             *span,
                                             Some(0),

crates/nu-protocol/src/pipeline_data.rs

@@ -605,7 +605,7 @@ impl PipelineData {
                     .map(|bytes| bytes.item)
                     .unwrap_or_default();
                 RawStream::new(
-                    Box::new(vec![Ok(stderr_bytes)].into_iter()),
+                    Box::new(std::iter::once(Ok(stderr_bytes))),
                     stderr_ctrlc,
                     stderr_span,
                     None,

crates/nu-test-support/src/playground/nu_process.rs

@@ -82,7 +82,7 @@ impl NuProcess {
 
         command.env_clear();
 
-        let paths = vec![test_bins_path()];
+        let paths = [test_bins_path()];
 
         let paths_joined = match std::env::join_paths(paths) {
             Ok(all) => all,