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-cli/src/completions/completer.rs

@@ -92,7 +92,7 @@ impl NuCompleter {
  &self.engine_state,
  &mut callee_stack,
  block,
- PipelineData::new(span),
+ PipelineData::empty(),
  true,
  true,
  );

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

@@ -67,7 +67,7 @@ impl Completer for CustomCompletion {
  redirect_stdout: true,
  redirect_stderr: true,
  },
- PipelineData::new(span),
+ PipelineData::empty(),
  );
 
  let mut custom_completion_options = None;

crates/nu-cli/src/config_files.rs

@@ -8,7 +8,7 @@ use nu_path::canonicalize_with;
 use nu_protocol::engine::{EngineState, Stack, StateWorkingSet};
 #[cfg(feature = "plugin")]
 use nu_protocol::Spanned;
-use nu_protocol::{HistoryFileFormat, PipelineData, Span};
+use nu_protocol::{HistoryFileFormat, PipelineData};
 use std::path::PathBuf;
 
 #[cfg(feature = "plugin")]
@@ -38,7 +38,7 @@ pub fn read_plugin_file(
  stack,
  &contents,
  &plugin_filename,
- PipelineData::new(Span::new(0, 0)),
+ PipelineData::empty(),
  );
  }
  }
@@ -85,7 +85,7 @@ pub fn eval_config_contents(
  stack,
  &contents,
  &config_filename,
- PipelineData::new(Span::new(0, 0)),
+ PipelineData::empty(),
  );
 
  // Merge the environment in case env vars changed in the config

crates/nu-cli/src/eval_file.rs

@@ -39,13 +39,7 @@ pub fn evaluate_file(
  if working_set.find_decl(b"main", &Type::Any).is_some() {
  let args = format!("main {}", args.join(" "));
 
- if !eval_source(
- engine_state,
- stack,
- &file,
- &path,
- PipelineData::new(Span::new(0, 0)),
- ) {
+ if !eval_source(engine_state, stack, &file, &path, PipelineData::empty()) {
  std::process::exit(1);
  }
  if !eval_source(engine_state, stack, args.as_bytes(), "<commandline>", input) {

crates/nu-cli/src/print.rs

@@ -50,14 +50,13 @@ Since this command has no output, there is no point in piping it with other comm
  let args: Vec<Value> = call.rest(engine_state, stack, 0)?;
  let no_newline = call.has_flag("no-newline");
  let to_stderr = call.has_flag("stderr");
- let head = call.head;
 
  for arg in args {
  arg.into_pipeline_data()
  .print(engine_state, stack, no_newline, to_stderr)?;
  }
 
- Ok(PipelineData::new(head))
+ Ok(PipelineData::empty())
  }
 
  fn examples(&self) -> Vec<Example> {

crates/nu-cli/src/prompt_update.rs

@@ -4,7 +4,7 @@ use log::info;
 use nu_engine::eval_subexpression;
 use nu_protocol::{
  engine::{EngineState, Stack, StateWorkingSet},
- Config, PipelineData, Span, Value,
+ Config, PipelineData, Value,
 };
 use reedline::Prompt;
 
@@ -37,12 +37,8 @@ fn get_prompt_string(
  let block = engine_state.get_block(block_id);
  let mut stack = stack.captures_to_stack(&captures);
  // Use eval_subexpression to force a redirection of output, so we can use everything in prompt
- let ret_val = eval_subexpression(
- engine_state,
- &mut stack,
- block,
- PipelineData::new(Span::new(0, 0)), // Don't try this at home, 0 span is ignored
- );
+ let ret_val =
+ eval_subexpression(engine_state, &mut stack, block, PipelineData::empty());
  info!(
  "get_prompt_string (block) {}:{}:{}",
  file!(),
@@ -62,12 +58,7 @@ fn get_prompt_string(
  Value::Block { val: block_id, .. } => {
  let block = engine_state.get_block(block_id);
  // Use eval_subexpression to force a redirection of output, so we can use everything in prompt
- let ret_val = eval_subexpression(
- engine_state,
- stack,
- block,
- PipelineData::new(Span::new(0, 0)), // Don't try this at home, 0 span is ignored
- );
+ let ret_val = eval_subexpression(engine_state, stack, block, PipelineData::empty());
  info!(
  "get_prompt_string (block) {}:{}:{}",
  file!(),

crates/nu-cli/src/repl.rs

@@ -149,7 +149,7 @@ pub fn evaluate_repl(
  stack,
  s.item.as_bytes(),
  &format!("entry #{}", entry_num),
- PipelineData::new(Span::new(0, 0)),
+ PipelineData::empty(),
  );
  engine_state.merge_env(stack, get_guaranteed_cwd(engine_state, stack))?;
  }
@@ -431,7 +431,7 @@ pub fn evaluate_repl(
  stack,
  s.as_bytes(),
  &format!("entry #{}", entry_num),
- PipelineData::new(Span::new(0, 0)),
+ PipelineData::empty(),
  );
  }
  let cmd_duration = start_time.elapsed();
@@ -637,7 +637,7 @@ pub fn eval_string_with_input(
 
  let input_as_pipeline_data = match input {
  Some(input) => PipelineData::Value(input, None),
- None => PipelineData::new(Span::test_data()),
+ None => PipelineData::empty(),
  };
 
  eval_block(
@@ -722,7 +722,7 @@ pub fn eval_hook(
  val: "condition".to_string(),
  span: value_span,
  };
- let mut output = PipelineData::new(Span::new(0, 0));
+ let mut output = PipelineData::empty();
 
  let code_path = PathMember::String {
  val: "code".to_string(),
@@ -823,7 +823,7 @@ pub fn eval_hook(
  };
 
  engine_state.merge_delta(delta)?;
- let input = PipelineData::new(value_span);
+ let input = PipelineData::empty();
 
  let var_ids: Vec<VarId> = vars
  .into_iter()
@@ -943,7 +943,7 @@ pub fn run_hook_block(
 ) -> Result<Value, ShellError> {
  let block = engine_state.get_block(block_id);
 
- let input = optional_input.unwrap_or_else(|| PipelineData::new(span));
+ let input = optional_input.unwrap_or_else(PipelineData::empty);
 
  let mut callee_stack = stack.gather_captures(&block.captures);
 

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> {