Improve empty pipelines (#7383)

# Description

This fix changes pipelines to allow them to actually be empty. Mapping
over empty pipelines gives empty pipelines. Empty pipelines immediately
return `None` when iterated.

This removes a some of where `Span::new(0, 0)` was coming from, though
there are other cases where we still use it.

# User-Facing Changes

None

# 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/core_commands/alias.rs

@@ -43,10 +43,10 @@ impl Command for Alias {
         &self,
         _engine_state: &EngineState,
         _stack: &mut Stack,
-        call: &Call,
+        _call: &Call,
         _input: PipelineData,
     ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/ast.rs

@@ -37,14 +37,13 @@ impl Command for Ast {
         call: &Call,
         _input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
-        let head = call.head;
         let pipeline: Spanned<String> = call.req(engine_state, stack, 0)?;
         let mut working_set = StateWorkingSet::new(engine_state);
 
         let (output, err) = parse(&mut working_set, None, pipeline.item.as_bytes(), false, &[]);
         eprintln!("output: {:#?}\nerror: {:#?}", output, err);
 
-        Ok(PipelineData::new(head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/def.rs

@@ -36,10 +36,10 @@ impl Command for Def {
         &self,
         _engine_state: &EngineState,
         _stack: &mut Stack,
-        call: &Call,
+        _call: &Call,
         _input: PipelineData,
     ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/def_env.rs

@@ -62,10 +62,10 @@ def-env cd_with_fallback [arg = ""] {
         &self,
         _engine_state: &EngineState,
         _stack: &mut Stack,
-        call: &Call,
+        _call: &Call,
         _input: PipelineData,
     ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/do_.rs

@@ -169,9 +169,9 @@ impl Command for Do {
                 trim_end_newline,
             }),
             Ok(PipelineData::Value(Value::Error { .. }, ..)) if ignore_shell_errors => {
-                Ok(PipelineData::new(call.head))
+                Ok(PipelineData::empty())
             }
-            Err(_) if ignore_shell_errors => Ok(PipelineData::new(call.head)),
+            Err(_) if ignore_shell_errors => Ok(PipelineData::empty()),
             r => r,
         }
     }

crates/nu-command/src/core_commands/export_alias.rs

@@ -39,10 +39,10 @@ impl Command for ExportAlias {
         &self,
         _engine_state: &EngineState,
         _stack: &mut Stack,
-        call: &Call,
+        _call: &Call,
         _input: PipelineData,
     ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/export_def.rs

@@ -36,10 +36,10 @@ impl Command for ExportDef {
         &self,
         _engine_state: &EngineState,
         _stack: &mut Stack,
-        call: &Call,
+        _call: &Call,
         _input: PipelineData,
     ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/export_def_env.rs

@@ -62,10 +62,10 @@ export def-env cd_with_fallback [arg = ""] {
         &self,
         _engine_state: &EngineState,
         _stack: &mut Stack,
-        call: &Call,
+        _call: &Call,
         _input: PipelineData,
     ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/export_extern.rs

@@ -35,10 +35,10 @@ impl Command for ExportExtern {
         &self,
         _engine_state: &EngineState,
         _stack: &mut Stack,
-        call: &Call,
+        _call: &Call,
         _input: PipelineData,
     ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/export_use.rs

@@ -34,10 +34,10 @@ impl Command for ExportUse {
         &self,
         _engine_state: &EngineState,
         _stack: &mut Stack,
-        call: &Call,
+        _call: &Call,
         _input: PipelineData,
     ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/extern_.rs

@@ -35,10 +35,10 @@ impl Command for Extern {
         &self,
         _engine_state: &EngineState,
         _stack: &mut Stack,
-        call: &Call,
+        _call: &Call,
         _input: PipelineData,
     ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/for_.rs

@@ -110,7 +110,7 @@ impl Command for For {
                         &engine_state,
                         stack,
                         &block,
-                        PipelineData::new(head),
+                        PipelineData::empty(),
                         redirect_stdout,
                         redirect_stderr,
                     ) {
@@ -155,7 +155,7 @@ impl Command for For {
                         &engine_state,
                         stack,
                         &block,
-                        PipelineData::new(head),
+                        PipelineData::empty(),
                         redirect_stdout,
                         redirect_stderr,
                     ) {
@@ -181,14 +181,14 @@ impl Command for For {
                     &engine_state,
                     stack,
                     &block,
-                    PipelineData::new(head),
+                    PipelineData::empty(),
                     redirect_stdout,
                     redirect_stderr,
                 )?
                 .into_value(head);
             }
         }
-        Ok(PipelineData::new(head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/hide.rs

@@ -62,7 +62,7 @@ This command is a parser keyword. For details, check:
 
         stack.remove_env_var(engine_state, &env_var_name.item);
 
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/hide_env.rs

@@ -63,7 +63,7 @@ impl Command for HideEnv {
             }
         }
 
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/if_.rs

@@ -102,7 +102,7 @@ impl Command for If {
                         .map(|res| res.0)
                     }
                 } else {
-                    Ok(PipelineData::new(call.head))
+                    Ok(PipelineData::empty())
                 }
             }
             x => Err(ShellError::CantConvert(

crates/nu-command/src/core_commands/ignore.rs

@@ -32,7 +32,7 @@ impl Command for Ignore {
         input: PipelineData,
     ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
         input.into_value(call.head);
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/let_.rs

@@ -73,7 +73,7 @@ impl Command for Let {
         //println!("Adding: {:?} to {}", rhs, var_id);
 
         stack.add_var(var_id, rhs.into_value(call.head));
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/loop_.rs

@@ -55,7 +55,7 @@ impl Command for Loop {
                 engine_state,
                 stack,
                 block,
-                PipelineData::new(call.head),
+                PipelineData::empty(),
                 call.redirect_stdout,
                 call.redirect_stderr,
             ) {
@@ -73,7 +73,7 @@ impl Command for Loop {
                 }
             }
         }
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/module.rs

@@ -35,10 +35,10 @@ impl Command for Module {
         &self,
         _engine_state: &EngineState,
         _stack: &mut Stack,
-        call: &Call,
+        _call: &Call,
         _input: PipelineData,
     ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/mut_.rs

@@ -73,7 +73,7 @@ impl Command for Mut {
         //println!("Adding: {:?} to {}", rhs, var_id);
 
         stack.add_var(var_id, rhs.into_value(call.head));
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/overlay/hide.rs

@@ -88,7 +88,7 @@ impl Command for OverlayHide {
             stack.add_env_var(name, val);
         }
 
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/overlay/new.rs

@@ -49,7 +49,7 @@ This command is a parser keyword. For details, check:
 
         stack.add_overlay(name_arg.item);
 
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/overlay/use_.rs

@@ -172,7 +172,7 @@ impl Command for OverlayUse {
             caller_stack.add_overlay(overlay_name);
         }
 
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/register.rs

@@ -49,10 +49,10 @@ impl Command for Register {
         &self,
         _engine_state: &EngineState,
         _stack: &mut Stack,
-        call: &Call,
+        _call: &Call,
         _input: PipelineData,
     ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/try_.rs

@@ -71,12 +71,12 @@ impl Command for Try {
                         engine_state,
                         stack,
                         catch_block,
-                        PipelineData::new(call.head),
+                        PipelineData::empty(),
                         false,
                         false,
                     )
                 } else {
-                    Ok(PipelineData::new(call.head))
+                    Ok(PipelineData::empty())
                 }
             }
             // external command may fail to run
@@ -118,12 +118,12 @@ impl Command for Try {
                             engine_state,
                             stack,
                             catch_block,
-                            PipelineData::new(call.head),
+                            PipelineData::empty(),
                             false,
                             false,
                         )
                     } else {
-                        Ok(PipelineData::new(call.head))
+                        Ok(PipelineData::empty())
                     }
                 } else {
                     Ok(PipelineData::ExternalStream {

crates/nu-command/src/core_commands/use_.rs

@@ -112,7 +112,7 @@ impl Command for Use {
             ));
         }
 
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/core_commands/while_.rs

@@ -63,7 +63,7 @@ impl Command for While {
                             engine_state,
                             stack,
                             block,
-                            PipelineData::new(call.head),
+                            PipelineData::empty(),
                             call.redirect_stdout,
                             call.redirect_stderr,
                         ) {
@@ -94,7 +94,7 @@ impl Command for While {
                 }
             }
         }
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/dataframe/test_dataframe.rs

@@ -22,7 +22,7 @@ pub fn test_dataframe(cmds: Vec<Box<dyn Command + 'static>>) {
     let delta = {
         // Base functions that are needed for testing
         // Try to keep this working set small to keep tests running as fast as possible
-        let mut working_set = StateWorkingSet::new(&*engine_state);
+        let mut working_set = StateWorkingSet::new(&engine_state);
         working_set.add_decl(Box::new(Let));
         working_set.add_decl(Box::new(ToDataFrame));
         working_set.add_decl(Box::new(ToLazyFrame));
@@ -49,7 +49,7 @@ pub fn test_dataframe(cmds: Vec<Box<dyn Command + 'static>>) {
         let start = std::time::Instant::now();
 
         let (block, delta) = {
-            let mut working_set = StateWorkingSet::new(&*engine_state);
+            let mut working_set = StateWorkingSet::new(&engine_state);
             let (output, err) = parse(
                 &mut working_set,
                 None,
@@ -75,7 +75,7 @@ pub fn test_dataframe(cmds: Vec<Box<dyn Command + 'static>>) {
             &engine_state,
             &mut stack,
             &block,
-            PipelineData::new(Span::test_data()),
+            PipelineData::empty(),
             true,
             true,
         ) {

crates/nu-command/src/env/config/config_reset.rs

@@ -108,6 +108,6 @@ impl Command for ConfigReset {
                 }
             }
         }
-        Ok(PipelineData::new(span))
+        Ok(PipelineData::empty())
     }
 }

crates/nu-command/src/env/export_env.rs

@@ -50,7 +50,7 @@ impl Command for ExportEnv {
 
         redirect_env(engine_state, caller_stack, &callee_stack);
 
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/env/let_env.rs

@@ -57,7 +57,7 @@ impl Command for LetEnv {
         } else {
             stack.add_env_var(env_var.item, rhs);
         }
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/env/load_env.rs

@@ -57,7 +57,7 @@ impl Command for LoadEnv {
                         stack.add_env_var(env_var, rhs);
                     }
                 }
-                Ok(PipelineData::new(call.head))
+                Ok(PipelineData::empty())
             }
             None => match input {
                 PipelineData::Value(Value::Record { cols, vals, .. }, ..) => {
@@ -81,7 +81,7 @@ impl Command for LoadEnv {
                             stack.add_env_var(env_var, rhs);
                         }
                     }
-                    Ok(PipelineData::new(call.head))
+                    Ok(PipelineData::empty())
                 }
                 _ => Err(ShellError::UnsupportedInput(
                     "'load-env' expects a single record".into(),

crates/nu-command/src/example_test.rs

@@ -59,7 +59,7 @@ mod test_examples {
         let delta = {
             // Base functions that are needed for testing
             // Try to keep this working set small to keep tests running as fast as possible
-            let mut working_set = StateWorkingSet::new(&*engine_state);
+            let mut working_set = StateWorkingSet::new(&engine_state);
             working_set.add_decl(Box::new(Let));
             working_set.add_decl(Box::new(Str));
             working_set.add_decl(Box::new(StrJoin));
@@ -215,10 +215,10 @@ mod test_examples {
         );
 
         engine_state
-            .merge_env(&mut stack, &cwd)
+            .merge_env(&mut stack, cwd)
             .expect("Error merging environment");
 
-        let empty_input = PipelineData::new(Span::test_data());
+        let empty_input = PipelineData::empty();
         let result = eval(example.example, empty_input, cwd, engine_state);
 
         // Note. Value implements PartialEq for Bool, Int, Float, String and Block
@@ -320,7 +320,7 @@ mod test_examples {
                 block.pipelines[0].elements.truncate(&n_expressions - 1);
 
                 if !block.pipelines[0].elements.is_empty() {
-                    let empty_input = PipelineData::new(Span::test_data());
+                    let empty_input = PipelineData::empty();
                     Some(eval_block(block, empty_input, cwd, engine_state, delta))
                 } else {
                     Some(Value::nothing(Span::test_data()))

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

@@ -196,7 +196,7 @@ impl Command for Cd {
         match have_permission(&path_tointo) {
             PermissionResult::PermissionOk => {
                 stack.add_env_var("PWD".into(), path_value);
-                Ok(PipelineData::new(call.head))
+                Ok(PipelineData::empty())
             }
             PermissionResult::PermissionDenied(reason) => Err(ShellError::IOError(format!(
                 "Cannot change directory to {}: {}",

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

@@ -2,8 +2,7 @@ use nu_engine::CallExt;
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::{
-    Category, Example, PipelineData, RawStream, ShellError, Signature, Span, Spanned, SyntaxShape,
-    Value,
+    Category, Example, PipelineData, RawStream, ShellError, Signature, Spanned, SyntaxShape, Value,
 };
 use std::fs::File;
 use std::io::{BufWriter, Write};
@@ -160,7 +159,7 @@ impl Command for Save {
                         file.flush()?
                     }
 
-                    Ok(PipelineData::new(span))
+                    Ok(PipelineData::empty())
                 }
                 Value::Binary { val, .. } => {
                     if let Err(err) = file.write_all(&val) {
@@ -169,7 +168,7 @@ impl Command for Save {
                         file.flush()?
                     }
 
-                    Ok(PipelineData::new(span))
+                    Ok(PipelineData::empty())
                 }
                 Value::List { vals, .. } => {
                     let val = vals
@@ -185,7 +184,7 @@ impl Command for Save {
                         file.flush()?
                     }
 
-                    Ok(PipelineData::new(span))
+                    Ok(PipelineData::empty())
                 }
                 v => Err(ShellError::UnsupportedInput(
                     format!("{:?} not supported", v.get_type()),
@@ -194,7 +193,7 @@ impl Command for Save {
             }
         } else {
             match input {
-                PipelineData::ExternalStream { stdout: None, .. } => Ok(PipelineData::new(span)),
+                PipelineData::ExternalStream { stdout: None, .. } => Ok(PipelineData::empty()),
                 PipelineData::ExternalStream {
                     stdout: Some(stream),
                     stderr,
@@ -202,16 +201,16 @@ impl Command for Save {
                 } => {
                     // delegate a thread to redirect stderr to result.
                     let handler = stderr.map(|stderr_stream| match stderr_file {
-                        Some(stderr_file) => std::thread::spawn(move || {
-                            stream_to_file(stderr_stream, stderr_file, span)
-                        }),
+                        Some(stderr_file) => {
+                            std::thread::spawn(move || stream_to_file(stderr_stream, stderr_file))
+                        }
                         None => std::thread::spawn(move || {
                             let _ = stderr_stream.into_bytes();
-                            Ok(PipelineData::new(span))
+                            Ok(PipelineData::empty())
                         }),
                     });
 
-                    let res = stream_to_file(stream, file, span);
+                    let res = stream_to_file(stream, file);
                     if let Some(h) = handler {
                         match h.join() {
                             Err(err) => {
@@ -236,7 +235,7 @@ impl Command for Save {
                             file.flush()?
                         }
 
-                        Ok(PipelineData::new(span))
+                        Ok(PipelineData::empty())
                     }
                     Value::Binary { val, .. } => {
                         if let Err(err) = file.write_all(&val) {
@@ -245,7 +244,7 @@ impl Command for Save {
                             file.flush()?
                         }
 
-                        Ok(PipelineData::new(span))
+                        Ok(PipelineData::empty())
                     }
                     Value::List { vals, .. } => {
                         let val = vals
@@ -261,7 +260,7 @@ impl Command for Save {
                             file.flush()?
                         }
 
-                        Ok(PipelineData::new(span))
+                        Ok(PipelineData::empty())
                     }
                     v => Err(ShellError::UnsupportedInput(
                         format!("{:?} not supported", v.get_type()),
@@ -303,11 +302,7 @@ impl Command for Save {
     }
 }
 
-fn stream_to_file(
-    mut stream: RawStream,
-    file: File,
-    span: Span,
-) -> Result<PipelineData, ShellError> {
+fn stream_to_file(mut stream: RawStream, file: File) -> Result<PipelineData, ShellError> {
     let mut writer = BufWriter::new(file);
 
     stream
@@ -331,5 +326,5 @@ fn stream_to_file(
             }
             Ok(())
         })
-        .map(|_| PipelineData::new(span))
+        .map(|_| PipelineData::empty())
 }

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

@@ -190,7 +190,7 @@ impl Command for Touch {
             }
         }
 
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

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

@@ -271,7 +271,7 @@ impl Command for Watch {
             }
         }
 
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

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

@@ -72,6 +72,7 @@ fn getcol(
     input: PipelineData,
 ) -> Result<PipelineData, ShellError> {
     match input {
+        PipelineData::Empty => Ok(PipelineData::Empty),
         PipelineData::Value(
             Value::List {
                 vals: input_vals,

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

@@ -156,6 +156,7 @@ with 'transpose' first."#
         let redirect_stderr = call.redirect_stderr;
 
         match input {
+            PipelineData::Empty => Ok(PipelineData::Empty),
             PipelineData::Value(Value::Range { .. }, ..)
             | PipelineData::Value(Value::List { .. }, ..)
             | PipelineData::ListStream { .. } => Ok(input
@@ -223,7 +224,7 @@ with 'transpose' first."#
                     }
                 })
                 .into_pipeline_data(ctrlc)),
-            PipelineData::ExternalStream { stdout: None, .. } => Ok(PipelineData::new(call.head)),
+            PipelineData::ExternalStream { stdout: None, .. } => Ok(PipelineData::empty()),
             PipelineData::ExternalStream {
                 stdout: Some(stream),
                 ..

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

@@ -116,6 +116,7 @@ impl Command for EachWhile {
         let redirect_stderr = call.redirect_stderr;
 
         match input {
+            PipelineData::Empty => Ok(PipelineData::Empty),
             PipelineData::Value(Value::Range { .. }, ..)
             | PipelineData::Value(Value::List { .. }, ..)
             | PipelineData::ListStream { .. } => Ok(input
@@ -186,7 +187,7 @@ impl Command for EachWhile {
                 })
                 .fuse()
                 .into_pipeline_data(ctrlc)),
-            PipelineData::ExternalStream { stdout: None, .. } => Ok(PipelineData::new(call.head)),
+            PipelineData::ExternalStream { stdout: None, .. } => Ok(PipelineData::empty()),
             PipelineData::ExternalStream {
                 stdout: Some(stream),
                 ..

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

@@ -103,6 +103,7 @@ fn empty(
         .into_pipeline_data())
     } else {
         match input {
+            PipelineData::Empty => Ok(PipelineData::Empty),
             PipelineData::ExternalStream { stdout, .. } => match stdout {
                 Some(s) => {
                     let bytes = s.into_bytes();

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

@@ -321,6 +321,7 @@ fn find_with_rest_and_highlight(
     let ls_colors = get_ls_colors(ls_colors_env_str);
 
     match input {
+        PipelineData::Empty => Ok(PipelineData::Empty),
         PipelineData::Value(_, _) => input
             .map(
                 move |mut x| match &mut x {
@@ -446,7 +447,7 @@ fn find_with_rest_and_highlight(
         )
         .into_pipeline_data(ctrlc)
         .set_metadata(meta)),
-        PipelineData::ExternalStream { stdout: None, .. } => Ok(PipelineData::new(span)),
+        PipelineData::ExternalStream { stdout: None, .. } => Ok(PipelineData::empty()),
         PipelineData::ExternalStream {
             stdout: Some(stream),
             ..

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

@@ -110,7 +110,7 @@ impl Command for Last {
             if let Some(last) = last {
                 Ok(last.into_pipeline_data().set_metadata(metadata))
             } else {
-                Ok(PipelineData::new(span).set_metadata(metadata))
+                Ok(PipelineData::empty().set_metadata(metadata))
             }
         }
     }

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

@@ -97,6 +97,7 @@ fn getcol(
     input: PipelineData,
 ) -> Result<PipelineData, ShellError> {
     match input {
+        PipelineData::Empty => Ok(PipelineData::Empty),
         PipelineData::Value(
             Value::List {
                 vals: input_vals,

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

@@ -71,6 +71,7 @@ impl Command for Lines {
 
                 Ok(iter.into_pipeline_data(engine_state.ctrlc.clone()))
             }
+            PipelineData::Empty => Ok(PipelineData::Empty),
             PipelineData::ListStream(stream, ..) => {
                 let iter = stream
                     .into_iter()
@@ -112,7 +113,7 @@ impl Command for Lines {
                 format!("Not supported input: {}", val.as_string()?),
                 head,
             )),
-            PipelineData::ExternalStream { stdout: None, .. } => Ok(PipelineData::new(head)),
+            PipelineData::ExternalStream { stdout: None, .. } => Ok(PipelineData::empty()),
             PipelineData::ExternalStream {
                 stdout: Some(stream),
                 ..

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

@@ -81,6 +81,7 @@ impl Command for ParEach {
         let redirect_stderr = call.redirect_stderr;
 
         match input {
+            PipelineData::Empty => Ok(PipelineData::Empty),
             PipelineData::Value(Value::Range { val, .. }, ..) => Ok(val
                 .into_range_iter(ctrlc.clone())?
                 .enumerate()
@@ -272,7 +273,7 @@ impl Command for ParEach {
                 .into_iter()
                 .flatten()
                 .into_pipeline_data(ctrlc)),
-            PipelineData::ExternalStream { stdout: None, .. } => Ok(PipelineData::new(call.head)),
+            PipelineData::ExternalStream { stdout: None, .. } => Ok(PipelineData::empty()),
             PipelineData::ExternalStream {
                 stdout: Some(stream),
                 ..

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

@@ -219,7 +219,7 @@ impl Command for Reduce {
                 engine_state,
                 &mut stack,
                 block,
-                PipelineData::new(span),
+                PipelineData::empty(),
                 // redirect stdout until its the last input value
                 redirect_stdout || input_iter.peek().is_some(),
                 redirect_stderr,

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

@@ -249,7 +249,7 @@ fn select(
                 Ok(v.into_pipeline_data().set_metadata(metadata))
             }
         }
-        _ => Ok(PipelineData::new(span)),
+        _ => Ok(PipelineData::empty()),
     }
 }
 

crates/nu-command/src/filters/skip/skip_until.rs

@@ -96,7 +96,7 @@ impl Command for SkipUntil {
                     &engine_state,
                     &mut stack,
                     &block,
-                    PipelineData::new(span),
+                    PipelineData::empty(),
                     redirect_stdout,
                     redirect_stderr,
                 )

crates/nu-command/src/filters/skip/skip_while.rs

@@ -97,7 +97,7 @@ impl Command for SkipWhile {
                     &engine_state,
                     &mut stack,
                     &block,
-                    PipelineData::new(span),
+                    PipelineData::empty(),
                     redirect_stdout,
                     redirect_stderr,
                 )

crates/nu-command/src/filters/take/take_until.rs

@@ -92,7 +92,7 @@ impl Command for TakeUntil {
                     &engine_state,
                     &mut stack,
                     &block,
-                    PipelineData::new(span),
+                    PipelineData::empty(),
                     redirect_stdout,
                     redirect_stderr,
                 )

crates/nu-command/src/filters/take/take_while.rs

@@ -92,7 +92,7 @@ impl Command for TakeWhile {
                     &engine_state,
                     &mut stack,
                     &block,
-                    PipelineData::new(span),
+                    PipelineData::empty(),
                     redirect_stdout,
                     redirect_stderr,
                 )

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

@@ -62,6 +62,7 @@ impl Command for Where {
             let redirect_stderr = call.redirect_stderr;
 
             match input {
+                PipelineData::Empty => Ok(PipelineData::Empty),
                 PipelineData::Value(Value::Range { .. }, ..)
                 | PipelineData::Value(Value::List { .. }, ..)
                 | PipelineData::ListStream { .. } => Ok(input
@@ -115,9 +116,7 @@ impl Command for Where {
                         }
                     })
                     .into_pipeline_data(ctrlc)),
-                PipelineData::ExternalStream { stdout: None, .. } => {
-                    Ok(PipelineData::new(call.head))
-                }
+                PipelineData::ExternalStream { stdout: None, .. } => Ok(PipelineData::empty()),
                 PipelineData::ExternalStream {
                     stdout: Some(stream),
                     ..

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

@@ -39,6 +39,7 @@ impl Command for Wrap {
         let name: String = call.req(engine_state, stack, 0)?;
 
         match input {
+            PipelineData::Empty => Ok(PipelineData::Empty),
             PipelineData::Value(Value::Range { .. }, ..)
             | PipelineData::Value(Value::List { .. }, ..)
             | PipelineData::ListStream { .. } => Ok(input

crates/nu-command/src/misc/history.rs

@@ -54,7 +54,7 @@ impl Command for History {
             if clear {
                 let _ = std::fs::remove_file(history_path);
                 // TODO: FIXME also clear the auxiliary files when using sqlite
-                Ok(PipelineData::new(head))
+                Ok(PipelineData::empty())
             } else {
                 let history_reader: Option<Box<dyn ReedlineHistory>> =
                     match engine_state.config.history_file_format {

crates/nu-command/src/network/fetch.rs

@@ -176,7 +176,7 @@ impl Command for SubCommand {
                                     file.flush()?
                                 }
 
-                                Ok(PipelineData::new(span))
+                                Ok(PipelineData::empty())
                             }
                             Value::Binary { val, .. } => {
                                 if let Err(err) = file.write_all(&val) {
@@ -185,7 +185,7 @@ impl Command for SubCommand {
                                     file.flush()?
                                 }
 
-                                Ok(PipelineData::new(span))
+                                Ok(PipelineData::empty())
                             }
                             Value::List { vals, .. } => {
                                 let val = vals
@@ -201,7 +201,7 @@ impl Command for SubCommand {
                                     file.flush()?
                                 }
 
-                                Ok(PipelineData::new(span))
+                                Ok(PipelineData::empty())
                             }
                             v => Err(ShellError::UnsupportedInput(
                                 format!("{:?} not supported", v.get_type()),
@@ -211,7 +211,7 @@ impl Command for SubCommand {
                     } else {
                         match value {
                             PipelineData::ExternalStream { stdout: None, .. } => {
-                                Ok(PipelineData::new(span))
+                                Ok(PipelineData::empty())
                             }
                             PipelineData::ExternalStream {
                                 stdout: Some(mut stream),
@@ -240,7 +240,7 @@ impl Command for SubCommand {
                                         }
                                         Ok(())
                                     })
-                                    .map(|_| PipelineData::new(span))
+                                    .map(|_| PipelineData::empty())
                             }
                             value => match value.into_value(span) {
                                 Value::String { val, .. } => {
@@ -250,7 +250,7 @@ impl Command for SubCommand {
                                         file.flush()?
                                     }
 
-                                    Ok(PipelineData::new(span))
+                                    Ok(PipelineData::empty())
                                 }
                                 Value::Binary { val, .. } => {
                                     if let Err(err) = file.write_all(&val) {
@@ -259,7 +259,7 @@ impl Command for SubCommand {
                                         file.flush()?
                                     }
 
-                                    Ok(PipelineData::new(span))
+                                    Ok(PipelineData::empty())
                                 }
                                 Value::List { vals, .. } => {
                                     let val = vals
@@ -275,7 +275,7 @@ impl Command for SubCommand {
                                         file.flush()?
                                     }
 
-                                    Ok(PipelineData::new(span))
+                                    Ok(PipelineData::empty())
                                 }
                                 v => Err(ShellError::UnsupportedInput(
                                     format!("{:?} not supported", v.get_type()),

crates/nu-command/src/shells/enter.rs

@@ -99,7 +99,7 @@ impl Command for Enter {
 
         stack.add_env_var("PWD".into(), new_path);
 
-        Ok(PipelineData::new(call.head))
+        Ok(PipelineData::empty())
     }
 
     fn examples(&self) -> Vec<Example> {

crates/nu-command/src/shells/exit.rs

@@ -101,7 +101,7 @@ impl Command for Exit {
 
             stack.add_env_var("PWD".into(), new_path);
 
-            Ok(PipelineData::new(call.head))
+            Ok(PipelineData::empty())
         }
     }
 

crates/nu-command/src/shells/mod.rs

@@ -121,7 +121,7 @@ fn switch_shell(
 
     stack.add_env_var("PWD".into(), new_path);
 
-    Ok(PipelineData::new(call.head))
+    Ok(PipelineData::empty())
 }
 
 fn list_shells(

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

@@ -180,7 +180,7 @@ fn detect_columns(
         })
         .into_pipeline_data(ctrlc))
     } else {
-        Ok(PipelineData::new(name_span))
+        Ok(PipelineData::empty())
     }
 }
 

crates/nu-command/src/strings/encode_decode/decode.rs

@@ -66,7 +66,7 @@ documentation link at https://docs.rs/encoding_rs/0.8.28/encoding_rs/#statics"#
         let encoding: Spanned<String> = call.req(engine_state, stack, 0)?;
 
         match input {
-            PipelineData::ExternalStream { stdout: None, .. } => Ok(PipelineData::new(call.head)),
+            PipelineData::ExternalStream { stdout: None, .. } => Ok(PipelineData::empty()),
             PipelineData::ExternalStream {
                 stdout: Some(stream),
                 ..

crates/nu-command/src/strings/encode_decode/encode.rs

@@ -66,7 +66,7 @@ documentation link at https://docs.rs/encoding_rs/0.8.28/encoding_rs/#statics"#
         let encoding: Spanned<String> = call.req(engine_state, stack, 0)?;
 
         match input {
-            PipelineData::ExternalStream { stdout: None, .. } => Ok(PipelineData::new(call.head)),
+            PipelineData::ExternalStream { stdout: None, .. } => Ok(PipelineData::empty()),
             PipelineData::ExternalStream {
                 stdout: Some(stream),
                 ..

crates/nu-command/src/system/benchmark.rs

@@ -44,7 +44,7 @@ impl Command for Benchmark {
             engine_state,
             &mut stack,
             block,
-            PipelineData::new(call.head),
+            PipelineData::empty(),
             redirect_stdout,
             redirect_stderr,
         )?

crates/nu-command/src/viewers/griddle.rs

@@ -88,7 +88,7 @@ prints out the list properly."#
                         use_grid_icons,
                     )?)
                 } else {
-                    Ok(PipelineData::new(call.head))
+                    Ok(PipelineData::empty())
                 }
             }
             PipelineData::ListStream(stream, ..) => {
@@ -106,7 +106,7 @@ prints out the list properly."#
                     )?)
                 } else {
                     // dbg!(data);
-                    Ok(PipelineData::new(call.head))
+                    Ok(PipelineData::empty())
                 }
             }
             PipelineData::Value(Value::Record { cols, vals, .. }, ..) => {