Merge remote-tracking branch 'origin/main' into plugin-ctrlc

Cargo.lock

@@ -3344,6 +3344,8 @@ dependencies = [
  "chrono",
  "chrono-humanize",
  "convert_case",
+ "dirs",
+ "dirs-sys",
  "fancy-regex",
  "indexmap",
  "log",
@@ -3367,6 +3369,7 @@ dependencies = [
  "tempfile",
  "thiserror",
  "typetag",
+ "windows-sys 0.48.0",
 ]
 
 [[package]]

Cargo.toml

@@ -84,6 +84,7 @@ deunicode = "1.6.0"
 dialoguer = { default-features = false, version = "0.11" }
 digest = { default-features = false, version = "0.10" }
 dirs = "5.0"
+dirs-sys = "0.4"
 dtparse = "2.0"
 encoding_rs = "0.8"
 fancy-regex = "0.13"
@@ -178,6 +179,7 @@ v_htmlescape = "0.15.0"
 wax = "0.6"
 which = "6.0.0"
 windows = "0.54"
+windows-sys = "0.48"
 winreg = "0.52"
 
 [dependencies]

crates/nu-cli/src/syntax_highlight.rs

@@ -429,6 +429,14 @@ fn find_matching_block_end_in_expr(
                 )
             }),
 
+            Expr::Collect(_, expr) => find_matching_block_end_in_expr(
+                line,
+                working_set,
+                expr,
+                global_span_offset,
+                global_cursor_offset,
+            ),
+
             Expr::Block(block_id)
             | Expr::Closure(block_id)
             | Expr::RowCondition(block_id)

crates/nu-cli/tests/completions/mod.rs

@@ -833,7 +833,7 @@ fn variables_completions() {
         "plugin-path".into(),
         "startup-time".into(),
         "temp-path".into(),
-        "vendor-autoload-dir".into(),
+        "vendor-autoload-dirs".into(),
     ];
 
     // Match results

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

@@ -21,7 +21,9 @@ impl Command for Break {
 
     fn extra_usage(&self) -> &str {
         r#"This command is a parser keyword. For details, check:
-  https://www.nushell.sh/book/thinking_in_nu.html"#
+  https://www.nushell.sh/book/thinking_in_nu.html
+
+  break can only be used in while, loop, and for loops. It can not be used with each or other filter commands"#
     }
 
     fn command_type(&self) -> CommandType {

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

@@ -21,7 +21,9 @@ impl Command for Continue {
 
     fn extra_usage(&self) -> &str {
         r#"This command is a parser keyword. For details, check:
-  https://www.nushell.sh/book/thinking_in_nu.html"#
+  https://www.nushell.sh/book/thinking_in_nu.html
+
+  continue can only be used in while, loop, and for loops. It can not be used with each or other filter commands"#
     }
 
     fn command_type(&self) -> CommandType {

crates/nu-cmd-lang/src/example_support.rs

@@ -4,7 +4,7 @@ use nu_protocol::{
     ast::Block,
     debugger::WithoutDebug,
     engine::{StateDelta, StateWorkingSet},
-    Range,
+    report_error_new, Range,
 };
 use std::{
     sync::Arc,
@@ -124,7 +124,10 @@ pub fn eval_block(
 
     nu_engine::eval_block::<WithoutDebug>(engine_state, &mut stack, &block, input)
         .and_then(|data| data.into_value(Span::test_data()))
-        .unwrap_or_else(|err| panic!("test eval error in `{}`: {:?}", "TODO", err))
+        .unwrap_or_else(|err| {
+            report_error_new(engine_state, &err);
+            panic!("test eval error in `{}`: {:?}", "TODO", err)
+        })
 }
 
 pub fn check_example_evaluates_to_expected_output(

crates/nu-command/src/debug/metadata_set.rs

@@ -42,32 +42,32 @@ impl Command for MetadataSet {
         engine_state: &EngineState,
         stack: &mut Stack,
         call: &Call,
-        input: PipelineData,
+        mut input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
         let head = call.head;
         let ds_fp: Option<String> = call.get_flag(engine_state, stack, "datasource-filepath")?;
         let ds_ls = call.has_flag(engine_state, stack, "datasource-ls")?;
         let content_type: Option<String> = call.get_flag(engine_state, stack, "content-type")?;
-        let signals = engine_state.signals().clone();
+
-        let metadata = input
+        let mut metadata = match &mut input {
-            .metadata()
+            PipelineData::Value(_, metadata)
-            .clone()
+            | PipelineData::ListStream(_, metadata)
-            .unwrap_or_default()
+            | PipelineData::ByteStream(_, metadata) => metadata.take().unwrap_or_default(),
-            .with_content_type(content_type);
+            PipelineData::Empty => return Err(ShellError::PipelineEmpty { dst_span: head }),
+        };
+
+        if let Some(content_type) = content_type {
+            metadata.content_type = Some(content_type);
+        }
 
         match (ds_fp, ds_ls) {
-            (Some(path), false) => Ok(input.into_pipeline_data_with_metadata(
+            (Some(path), false) => metadata.data_source = DataSource::FilePath(path.into()),
-                head,
+            (None, true) => metadata.data_source = DataSource::Ls,
-                signals,
+            (Some(_), true) => (), // TODO: error here
-                metadata.with_data_source(DataSource::FilePath(path.into())),
+            (None, false) => (),
-            )),
-            (None, true) => Ok(input.into_pipeline_data_with_metadata(
-                head,
-                signals,
-                metadata.with_data_source(DataSource::Ls),
-            )),
-            _ => Ok(input.into_pipeline_data_with_metadata(head, signals, metadata)),
         }
+
+        Ok(input.set_metadata(Some(metadata)))
     }
 
     fn examples(&self) -> Vec<Example> {
@@ -85,7 +85,9 @@ impl Command for MetadataSet {
             Example {
                 description: "Set the metadata of a file path",
                 example: "'crates' | metadata set --content-type text/plain | metadata",
-                result: Some(Value::record(record!("content_type" => Value::string("text/plain", Span::test_data())), Span::test_data())),
+                result: Some(Value::test_record(record! {
+                    "content_type" => Value::test_string("text/plain"),
+                })),
             },
         ]
     }

crates/nu-command/src/example_test.rs

@@ -31,7 +31,7 @@ mod test_examples {
         check_example_evaluates_to_expected_output,
         check_example_input_and_output_types_match_command_signature,
     };
-    use nu_cmd_lang::{Break, Echo, If, Let, Mut};
+    use nu_cmd_lang::{Break, Describe, Echo, If, Let, Mut};
     use nu_protocol::{
         engine::{Command, EngineState, StateWorkingSet},
         Type,
@@ -81,6 +81,7 @@ mod test_examples {
             working_set.add_decl(Box::new(Break));
             working_set.add_decl(Box::new(Date));
             working_set.add_decl(Box::new(Default));
+            working_set.add_decl(Box::new(Describe));
             working_set.add_decl(Box::new(Each));
             working_set.add_decl(Box::new(Echo));
             working_set.add_decl(Box::new(Enumerate));

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

@@ -61,6 +61,7 @@ impl Command for Watch {
                 "Watch all directories under `<path>` recursively. Will be ignored if `<path>` is a file (default: true)",
                 Some('r'),
             )
+            .switch("quiet", "Hide the initial status message (default: false)", Some('q'))
             .switch("verbose", "Operate in verbose mode (default: false)", Some('v'))
             .category(Category::FileSystem)
     }
@@ -94,6 +95,8 @@ impl Command for Watch {
 
         let verbose = call.has_flag(engine_state, stack, "verbose")?;
 
+        let quiet = call.has_flag(engine_state, stack, "quiet")?;
+
         let debounce_duration_flag: Option<Spanned<i64>> =
             call.get_flag(engine_state, stack, "debounce-ms")?;
         let debounce_duration = match debounce_duration_flag {
@@ -161,7 +164,9 @@ impl Command for Watch {
         // need to cache to make sure that rename event works.
         debouncer.cache().add_root(&path, recursive_mode);
 
-        eprintln!("Now watching files at {path:?}. Press ctrl+c to abort.");
+        if !quiet {
+            eprintln!("Now watching files at {path:?}. Press ctrl+c to abort.");
+        }
 
         let mut closure = ClosureEval::new(engine_state, stack, closure);
 

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

@@ -1,5 +1,6 @@
 use nu_engine::command_prelude::*;
 use nu_protocol::ListStream;
+use std::num::NonZeroUsize;
 
 #[derive(Clone)]
 pub struct Chunks;
@@ -89,26 +90,33 @@ impl Command for Chunks {
                 span: chunk_size.span(),
             })?;
 
-        if size == 0 {
+        let size = NonZeroUsize::try_from(size).map_err(|_| ShellError::IncorrectValue {
-            return Err(ShellError::IncorrectValue {
+            msg: "`chunk_size` cannot be zero".into(),
-                msg: "`chunk_size` cannot be zero".into(),
+            val_span: chunk_size.span(),
-                val_span: chunk_size.span(),
+            call_span: head,
-                call_span: head,
+        })?;
-            });
-        }
 
-        match input {
+        chunks(engine_state, input, size, head)
-            PipelineData::Value(Value::List { vals, .. }, metadata) => {
+    }
-                let chunks = ChunksIter::new(vals, size, head);
+}
-                let stream = ListStream::new(chunks, head, engine_state.signals().clone());
+
-                Ok(PipelineData::ListStream(stream, metadata))
+pub fn chunks(
-            }
+    engine_state: &EngineState,
-            PipelineData::ListStream(stream, metadata) => {
+    input: PipelineData,
-                let stream = stream.modify(|iter| ChunksIter::new(iter, size, head));
+    chunk_size: NonZeroUsize,
-                Ok(PipelineData::ListStream(stream, metadata))
+    span: Span,
-            }
+) -> Result<PipelineData, ShellError> {
-            input => Err(input.unsupported_input_error("list", head)),
+    match input {
+        PipelineData::Value(Value::List { vals, .. }, metadata) => {
+            let chunks = ChunksIter::new(vals, chunk_size, span);
+            let stream = ListStream::new(chunks, span, engine_state.signals().clone());
+            Ok(PipelineData::ListStream(stream, metadata))
         }
+        PipelineData::ListStream(stream, metadata) => {
+            let stream = stream.modify(|iter| ChunksIter::new(iter, chunk_size, span));
+            Ok(PipelineData::ListStream(stream, metadata))
+        }
+        input => Err(input.unsupported_input_error("list", span)),
     }
 }
 
@@ -119,10 +127,10 @@ struct ChunksIter<I: Iterator<Item = Value>> {
 }
 
 impl<I: Iterator<Item = Value>> ChunksIter<I> {
-    fn new(iter: impl IntoIterator<IntoIter = I>, size: usize, span: Span) -> Self {
+    fn new(iter: impl IntoIterator<IntoIter = I>, size: NonZeroUsize, span: Span) -> Self {
         Self {
             iter: iter.into_iter(),
-            size,
+            size: size.into(),
             span,
         }
     }

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

@@ -132,8 +132,6 @@ with 'transpose' first."#
                             Ok(data) => Some(data.into_value(head).unwrap_or_else(|err| {
                                 Value::error(chain_error_with_input(err, is_error, span), span)
                             })),
-                            Err(ShellError::Continue { span }) => Some(Value::nothing(span)),
-                            Err(ShellError::Break { .. }) => None,
                             Err(error) => {
                                 let error = chain_error_with_input(error, is_error, span);
                                 Some(Value::error(error, span))
@@ -149,10 +147,6 @@ with 'transpose' first."#
                         .map_while(move |value| {
                             let value = match value {
                                 Ok(value) => value,
-                                Err(ShellError::Continue { span }) => {
-                                    return Some(Value::nothing(span))
-                                }
-                                Err(ShellError::Break { .. }) => return None,
                                 Err(err) => return Some(Value::error(err, head)),
                             };
 
@@ -163,8 +157,6 @@ with 'transpose' first."#
                                 .and_then(|data| data.into_value(head))
                             {
                                 Ok(value) => Some(value),
-                                Err(ShellError::Continue { span }) => Some(Value::nothing(span)),
-                                Err(ShellError::Break { .. }) => None,
                                 Err(error) => {
                                     let error = chain_error_with_input(error, is_error, span);
                                     Some(Value::error(error, span))

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

@@ -60,7 +60,6 @@ impl Command for Items {
 
                                 match result {
                                     Ok(value) => Some(value),
-                                    Err(ShellError::Break { .. }) => None,
                                     Err(err) => {
                                         let err = chain_error_with_input(err, false, span);
                                         Some(Value::error(err, head))

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

@@ -36,7 +36,7 @@ impl Command for Reduce {
     }
 
     fn usage(&self) -> &str {
-        "Aggregate a list to a single value using an accumulator closure."
+        "Aggregate a list (starting from the left) to a single value using an accumulator closure."
     }
 
     fn search_terms(&self) -> Vec<&str> {
@@ -50,6 +50,11 @@ impl Command for Reduce {
                 description: "Sum values of a list (same as 'math sum')",
                 result: Some(Value::test_int(10)),
             },
+            Example {
+                example: "[ 1 2 3 4 ] | reduce {|it, acc| $acc - $it }",
+                description: r#"`reduce` accumulates value from left to right, equivalent to (((1 - 2) - 3) - 4)."#,
+                result: Some(Value::test_int(-8)),
+            },
             Example {
                 example:
                     "[ 8 7 6 ] | enumerate | reduce --fold 0 {|it, acc| $acc + $it.item + $it.index }",
@@ -61,6 +66,11 @@ impl Command for Reduce {
                 description: "Sum values with a starting value (fold)",
                 result: Some(Value::test_int(20)),
             },
+            Example {
+                example: r#"[[foo baz] [baz quux]] | reduce --fold "foobar" {|it, acc| $acc | str replace $it.0 $it.1}"#,
+                description: "Iteratively perform string replace (from left to right): 'foobar' -> 'bazbar' -> 'quuxbar'",
+                result: Some(Value::test_string("quuxbar")),
+            },
             Example {
                 example: r#"[ i o t ] | reduce --fold "Arthur, King of the Britons" {|it, acc| $acc | str replace --all $it "X" }"#,
                 description: "Replace selected characters in a string with 'X'",

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

@@ -1,5 +1,6 @@
 use nu_engine::command_prelude::*;
-use nu_protocol::ValueIterator;
+use nu_protocol::ListStream;
+use std::num::NonZeroUsize;
 
 #[derive(Clone)]
 pub struct Window;
@@ -12,8 +13,8 @@ impl Command for Window {
     fn signature(&self) -> Signature {
         Signature::build("window")
             .input_output_types(vec![(
-                Type::List(Box::new(Type::Any)),
+                Type::list(Type::Any),
-                Type::List(Box::new(Type::List(Box::new(Type::Any)))),
+                Type::list(Type::list(Type::Any)),
             )])
             .required("window_size", SyntaxShape::Int, "The size of each window.")
             .named(
@@ -34,72 +35,41 @@ impl Command for Window {
         "Creates a sliding window of `window_size` that slide by n rows/elements across input."
     }
 
+    fn extra_usage(&self) -> &str {
+        "This command will error if `window_size` or `stride` are negative or zero."
+    }
+
     fn examples(&self) -> Vec<Example> {
-        let stream_test_1 = vec![
-            Value::list(
-                vec![Value::test_int(1), Value::test_int(2)],
-                Span::test_data(),
-            ),
-            Value::list(
-                vec![Value::test_int(2), Value::test_int(3)],
-                Span::test_data(),
-            ),
-            Value::list(
-                vec![Value::test_int(3), Value::test_int(4)],
-                Span::test_data(),
-            ),
-        ];
-
-        let stream_test_2 = vec![
-            Value::list(
-                vec![Value::test_int(1), Value::test_int(2)],
-                Span::test_data(),
-            ),
-            Value::list(
-                vec![Value::test_int(4), Value::test_int(5)],
-                Span::test_data(),
-            ),
-            Value::list(
-                vec![Value::test_int(7), Value::test_int(8)],
-                Span::test_data(),
-            ),
-        ];
-
-        let stream_test_3 = vec![
-            Value::list(
-                vec![Value::test_int(1), Value::test_int(2), Value::test_int(3)],
-                Span::test_data(),
-            ),
-            Value::list(
-                vec![Value::test_int(4), Value::test_int(5)],
-                Span::test_data(),
-            ),
-        ];
-
         vec![
             Example {
                 example: "[1 2 3 4] | window 2",
                 description: "A sliding window of two elements",
-                result: Some(Value::list(
+                result: Some(Value::test_list(vec![
-                    stream_test_1,
+                    Value::test_list(vec![Value::test_int(1), Value::test_int(2)]),
-                    Span::test_data(),
+                    Value::test_list(vec![Value::test_int(2), Value::test_int(3)]),
-                )),
+                    Value::test_list(vec![Value::test_int(3), Value::test_int(4)]),
+                ])),
             },
             Example {
                 example: "[1, 2, 3, 4, 5, 6, 7, 8] | window 2 --stride 3",
                 description: "A sliding window of two elements, with a stride of 3",
-                result: Some(Value::list(
+                result: Some(Value::test_list(vec![
-                    stream_test_2,
+                    Value::test_list(vec![Value::test_int(1), Value::test_int(2)]),
-                    Span::test_data(),
+                    Value::test_list(vec![Value::test_int(4), Value::test_int(5)]),
-                )),
+                    Value::test_list(vec![Value::test_int(7), Value::test_int(8)]),
+                ])),
             },
             Example {
                 example: "[1, 2, 3, 4, 5] | window 3 --stride 3 --remainder",
                 description: "A sliding window of equal stride that includes remainder. Equivalent to chunking",
-                result: Some(Value::list(
+                result: Some(Value::test_list(vec![
-                    stream_test_3,
+                    Value::test_list(vec![
-                    Span::test_data(),
+                        Value::test_int(1),
-                )),
+                        Value::test_int(2),
+                        Value::test_int(3),
+                    ]),
+                    Value::test_list(vec![Value::test_int(4), Value::test_int(5)]),
+                ])),
             },
         ]
     }
@@ -112,116 +82,169 @@ impl Command for Window {
         input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
         let head = call.head;
-        let group_size: Spanned<usize> = call.req(engine_state, stack, 0)?;
+        let window_size: Value = call.req(engine_state, stack, 0)?;
-        let metadata = input.metadata();
+        let stride: Option<Value> = call.get_flag(engine_state, stack, "stride")?;
-        let stride: Option<usize> = call.get_flag(engine_state, stack, "stride")?;
         let remainder = call.has_flag(engine_state, stack, "remainder")?;
 
-        let stride = stride.unwrap_or(1);
+        let size =
+            usize::try_from(window_size.as_int()?).map_err(|_| ShellError::NeedsPositiveValue {
+                span: window_size.span(),
+            })?;
 
-        //FIXME: add in support for external redirection when engine-q supports it generally
+        let size = NonZeroUsize::try_from(size).map_err(|_| ShellError::IncorrectValue {
+            msg: "`window_size` cannot be zero".into(),
+            val_span: window_size.span(),
+            call_span: head,
+        })?;
 
-        let each_group_iterator = EachWindowIterator {
+        let stride = if let Some(stride_val) = stride {
-            group_size: group_size.item,
+            let stride = usize::try_from(stride_val.as_int()?).map_err(|_| {
-            input: Box::new(input.into_iter()),
+                ShellError::NeedsPositiveValue {
-            span: head,
+                    span: stride_val.span(),
-            previous: None,
+                }
-            stride,
+            })?;
-            remainder,
+
+            NonZeroUsize::try_from(stride).map_err(|_| ShellError::IncorrectValue {
+                msg: "`stride` cannot be zero".into(),
+                val_span: stride_val.span(),
+                call_span: head,
+            })?
+        } else {
+            NonZeroUsize::MIN
         };
 
-        Ok(each_group_iterator.into_pipeline_data_with_metadata(
+        if remainder && size == stride {
-            head,
+            super::chunks::chunks(engine_state, input, size, head)
-            engine_state.signals().clone(),
+        } else if stride >= size {
-            metadata,
+            match input {
-        ))
+                PipelineData::Value(Value::List { vals, .. }, metadata) => {
+                    let chunks = WindowGapIter::new(vals, size, stride, remainder, head);
+                    let stream = ListStream::new(chunks, head, engine_state.signals().clone());
+                    Ok(PipelineData::ListStream(stream, metadata))
+                }
+                PipelineData::ListStream(stream, metadata) => {
+                    let stream = stream
+                        .modify(|iter| WindowGapIter::new(iter, size, stride, remainder, head));
+                    Ok(PipelineData::ListStream(stream, metadata))
+                }
+                input => Err(input.unsupported_input_error("list", head)),
+            }
+        } else {
+            match input {
+                PipelineData::Value(Value::List { vals, .. }, metadata) => {
+                    let chunks = WindowOverlapIter::new(vals, size, stride, remainder, head);
+                    let stream = ListStream::new(chunks, head, engine_state.signals().clone());
+                    Ok(PipelineData::ListStream(stream, metadata))
+                }
+                PipelineData::ListStream(stream, metadata) => {
+                    let stream = stream
+                        .modify(|iter| WindowOverlapIter::new(iter, size, stride, remainder, head));
+                    Ok(PipelineData::ListStream(stream, metadata))
+                }
+                input => Err(input.unsupported_input_error("list", head)),
+            }
+        }
     }
 }
 
-struct EachWindowIterator {
+struct WindowOverlapIter<I: Iterator<Item = Value>> {
-    group_size: usize,
+    iter: I,
-    input: ValueIterator,
+    window: Vec<Value>,
-    span: Span,
-    previous: Option<Vec<Value>>,
     stride: usize,
     remainder: bool,
+    span: Span,
 }
 
-impl Iterator for EachWindowIterator {
+impl<I: Iterator<Item = Value>> WindowOverlapIter<I> {
+    fn new(
+        iter: impl IntoIterator<IntoIter = I>,
+        size: NonZeroUsize,
+        stride: NonZeroUsize,
+        remainder: bool,
+        span: Span,
+    ) -> Self {
+        Self {
+            iter: iter.into_iter(),
+            window: Vec::with_capacity(size.into()),
+            stride: stride.into(),
+            remainder,
+            span,
+        }
+    }
+}
+
+impl<I: Iterator<Item = Value>> Iterator for WindowOverlapIter<I> {
     type Item = Value;
 
     fn next(&mut self) -> Option<Self::Item> {
-        let mut group = self.previous.take().unwrap_or_else(|| {
+        let len = if self.window.is_empty() {
-            let mut vec = Vec::new();
+            self.window.capacity()
-
-            // We default to a Vec of capacity size + stride as striding pushes n extra elements to the end
-            vec.try_reserve(self.group_size + self.stride).ok();
-
-            vec
-        });
-        let mut current_count = 0;
-
-        if group.is_empty() {
-            loop {
-                let item = self.input.next();
-
-                match item {
-                    Some(v) => {
-                        group.push(v);
-
-                        current_count += 1;
-                        if current_count >= self.group_size {
-                            break;
-                        }
-                    }
-                    None => {
-                        if self.remainder {
-                            break;
-                        } else {
-                            return None;
-                        }
-                    }
-                }
-            }
         } else {
-            // our historic buffer is already full, so stride instead
+            self.stride
+        };
 
-            loop {
+        self.window.extend((&mut self.iter).take(len));
-                let item = self.input.next();
 
-                match item {
+        if self.window.len() == self.window.capacity()
-                    Some(v) => {
+            || (self.remainder && !self.window.is_empty())
-                        group.push(v);
+        {
-
+            let mut next = Vec::with_capacity(self.window.len());
-                        current_count += 1;
+            next.extend(self.window.iter().skip(self.stride).cloned());
-                        if current_count >= self.stride {
+            let window = std::mem::replace(&mut self.window, next);
-                            break;
+            Some(Value::list(window, self.span))
-                        }
+        } else {
-                    }
+            None
-                    None => {
-                        if self.remainder {
-                            break;
-                        } else {
-                            return None;
-                        }
-                    }
-                }
-            }
-
-            // We now have elements + stride in our group, and need to
-            // drop the skipped elements. Drain to preserve allocation and capacity
-            // Dropping this iterator consumes it.
-            group.drain(..self.stride.min(group.len()));
         }
+    }
+}
 
-        if group.is_empty() {
+struct WindowGapIter<I: Iterator<Item = Value>> {
-            return None;
+    iter: I,
+    size: usize,
+    skip: usize,
+    first: bool,
+    remainder: bool,
+    span: Span,
+}
+
+impl<I: Iterator<Item = Value>> WindowGapIter<I> {
+    fn new(
+        iter: impl IntoIterator<IntoIter = I>,
+        size: NonZeroUsize,
+        stride: NonZeroUsize,
+        remainder: bool,
+        span: Span,
+    ) -> Self {
+        let size = size.into();
+        Self {
+            iter: iter.into_iter(),
+            size,
+            skip: stride.get() - size,
+            first: true,
+            remainder,
+            span,
         }
+    }
+}
 
-        let return_group = group.clone();
+impl<I: Iterator<Item = Value>> Iterator for WindowGapIter<I> {
-        self.previous = Some(group);
+    type Item = Value;
 
-        Some(Value::list(return_group, self.span))
+    fn next(&mut self) -> Option<Self::Item> {
+        let mut window = Vec::with_capacity(self.size);
+        window.extend(
+            (&mut self.iter)
+                .skip(if self.first { 0 } else { self.skip })
+                .take(self.size),
+        );
+
+        self.first = false;
+
+        if window.len() == self.size || (self.remainder && !window.is_empty()) {
+            Some(Value::list(window, self.span))
+        } else {
+            None
+        }
     }
 }
 

crates/nu-command/src/generators/generate.rs

@@ -12,12 +12,12 @@ impl Command for Generate {
     fn signature(&self) -> Signature {
         Signature::build("generate")
             .input_output_types(vec![(Type::Nothing, Type::List(Box::new(Type::Any)))])
-            .required("initial", SyntaxShape::Any, "Initial value.")
             .required(
                 "closure",
                 SyntaxShape::Closure(Some(vec![SyntaxShape::Any])),
                 "Generator function.",
             )
+            .optional("initial", SyntaxShape::Any, "Initial value.")
             .allow_variants_without_examples(true)
             .category(Category::Generators)
     }
@@ -41,7 +41,7 @@ used as the next argument to the closure, otherwise generation stops.
     fn examples(&self) -> Vec<Example> {
         vec![
             Example {
-                example: "generate 0 {|i| if $i <= 10 { {out: $i, next: ($i + 2)} }}",
+                example: "generate {|i| if $i <= 10 { {out: $i, next: ($i + 2)} }} 0",
                 description: "Generate a sequence of numbers",
                 result: Some(Value::list(
                     vec![
@@ -57,10 +57,17 @@ used as the next argument to the closure, otherwise generation stops.
             },
             Example {
                 example:
-                    "generate [0, 1] {|fib| {out: $fib.0, next: [$fib.1, ($fib.0 + $fib.1)]} }",
+                    "generate {|fib| {out: $fib.0, next: [$fib.1, ($fib.0 + $fib.1)]} } [0, 1]",
                 description: "Generate a continuous stream of Fibonacci numbers",
                 result: None,
             },
+            Example {
+                example:
+                    "generate {|fib=[0, 1]| {out: $fib.0, next: [$fib.1, ($fib.0 + $fib.1)]} }",
+                description:
+                    "Generate a continuous stream of Fibonacci numbers, using default parameters",
+                result: None,
+            },
         ]
     }
 
@@ -72,15 +79,15 @@ used as the next argument to the closure, otherwise generation stops.
         _input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
         let head = call.head;
-        let initial: Value = call.req(engine_state, stack, 0)?;
+        let closure: Closure = call.req(engine_state, stack, 0)?;
-        let closure: Closure = call.req(engine_state, stack, 1)?;
+        let initial: Option<Value> = call.opt(engine_state, stack, 1)?;
-
+        let block = engine_state.get_block(closure.block_id);
         let mut closure = ClosureEval::new(engine_state, stack, closure);
 
         // A type of Option<S> is used to represent state. Invocation
         // will stop on None. Using Option<S> allows functions to output
         // one final value before stopping.
-        let mut state = Some(initial);
+        let mut state = Some(get_initial_state(initial, &block.signature, call.head)?);
         let iter = std::iter::from_fn(move || {
             let arg = state.take()?;
 
@@ -170,6 +177,38 @@ used as the next argument to the closure, otherwise generation stops.
     }
 }
 
+fn get_initial_state(
+    initial: Option<Value>,
+    signature: &Signature,
+    span: Span,
+) -> Result<Value, ShellError> {
+    match initial {
+        Some(v) => Ok(v),
+        None => {
+            // the initial state should be referred from signature
+            if !signature.optional_positional.is_empty()
+                && signature.optional_positional[0].default_value.is_some()
+            {
+                Ok(signature.optional_positional[0]
+                    .default_value
+                    .clone()
+                    .expect("Already checked default value"))
+            } else {
+                Err(ShellError::GenericError {
+                    error: "The initial value is missing".to_string(),
+                    msg: "Missing initial value".to_string(),
+                    span: Some(span),
+                    help: Some(
+                        "Provide an <initial> value as an argument to generate, or assign a default value to the closure parameter"
+                            .to_string(),
+                    ),
+                    inner: vec![],
+                })
+            }
+        }
+    }
+}
+
 #[cfg(test)]
 mod test {
     use super::*;

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

@@ -3,6 +3,7 @@ use nu_engine::command_prelude::*;
 
 use nu_protocol::Signals;
 use once_cell::sync::Lazy;
+use std::collections::HashSet;
 
 // Character used to separate directories in a Path Environment variable on windows is ";"
 #[cfg(target_family = "windows")]
@@ -149,6 +150,24 @@ static CHAR_MAP: Lazy<IndexMap<&'static str, String>> = Lazy::new(|| {
     }
 });
 
+static NO_OUTPUT_CHARS: Lazy<HashSet<&'static str>> = Lazy::new(|| {
+    [
+        // If the character is in the this set, we don't output it to prevent
+        // the broken of `char --list` command table format and alignment.
+        "newline",
+        "enter",
+        "nl",
+        "line_feed",
+        "lf",
+        "cr",
+        "crlf",
+        "bel",
+        "backspace",
+    ]
+    .into_iter()
+    .collect()
+});
+
 impl Command for Char {
     fn name(&self) -> &str {
         "char"
@@ -297,6 +316,11 @@ fn generate_character_list(signals: Signals, call_span: Span) -> PipelineData {
     CHAR_MAP
         .iter()
         .map(move |(name, s)| {
+            let character = if NO_OUTPUT_CHARS.contains(name) {
+                Value::string("", call_span)
+            } else {
+                Value::string(s, call_span)
+            };
             let unicode = Value::string(
                 s.chars()
                     .map(|c| format!("{:x}", c as u32))
@@ -306,7 +330,7 @@ fn generate_character_list(signals: Signals, call_span: Span) -> PipelineData {
             );
             let record = record! {
                 "name" => Value::string(*name, call_span),
-                "character" => Value::string(s, call_span),
+                "character" => character,
                 "unicode" => unicode,
             };
 

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

@@ -15,12 +15,3 @@ fn break_while_loop() {
 
     assert_eq!(actual.out, "hello");
 }
-
-#[test]
-fn break_each() {
-    let actual = nu!("
-        [1, 2, 3, 4, 5] | each {|x| if $x > 3 { break }; $x} | math sum
-        ");
-
-    assert_eq!(actual.out, "6");
-}

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

@@ -58,22 +58,6 @@ fn each_while_uses_enumerate_index() {
     assert_eq!(actual.out, "[0, 1, 2, 3]");
 }
 
-#[test]
-fn each_element_continue_command() {
-    let actual =
-        nu!("[1,2,3,4,6,7] | each { |x| if ($x mod 2 == 0) {continue} else { $x }} | to nuon");
-
-    assert_eq!(actual.out, "[1, 3, 7]");
-}
-
-#[test]
-fn each_element_break_command() {
-    let actual =
-        nu!("[1,2,5,4,6,7] | each { |x| if ($x mod 3 == 0) {break} else { $x }} | to nuon");
-
-    assert_eq!(actual.out, "[1, 2, 5, 4]");
-}
-
 #[test]
 fn errors_in_nested_each_show() {
     let actual = nu!("[[1,2]] | each {|x| $x | each {|y| error make {msg: \"oh noes\"} } }");

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

@@ -3,7 +3,7 @@ use nu_test_support::{nu, pipeline};
 #[test]
 fn generate_no_next_break() {
     let actual = nu!(
-        "generate 1 {|x| if $x == 3 { {out: $x}} else { {out: $x, next: ($x + 1)} }} | to nuon"
+        "generate {|x| if $x == 3 { {out: $x}} else { {out: $x, next: ($x + 1)} }} 1 | to nuon"
     );
 
     assert_eq!(actual.out, "[1, 2, 3]");
@@ -11,7 +11,7 @@ fn generate_no_next_break() {
 
 #[test]
 fn generate_null_break() {
-    let actual = nu!("generate 1 {|x| if $x <= 3 { {out: $x, next: ($x + 1)} }} | to nuon");
+    let actual = nu!("generate {|x| if $x <= 3 { {out: $x, next: ($x + 1)} }} 1 | to nuon");
 
     assert_eq!(actual.out, "[1, 2, 3]");
 }
@@ -20,13 +20,13 @@ fn generate_null_break() {
 fn generate_allows_empty_output() {
     let actual = nu!(pipeline(
         r#"
-        generate 0 {|x|
+        generate {|x|
           if $x == 1 {
             {next: ($x + 1)}
           } else if $x < 3 {
             {out: $x, next: ($x + 1)}
           }
-        } | to nuon
+        } 0 | to nuon
       "#
     ));
 
@@ -37,11 +37,11 @@ fn generate_allows_empty_output() {
 fn generate_allows_no_output() {
     let actual = nu!(pipeline(
         r#"
-        generate 0 {|x|
+        generate {|x|
           if $x < 3 {
             {next: ($x + 1)}
           }
-        } | to nuon
+        } 0 | to nuon
       "#
     ));
 
@@ -52,7 +52,7 @@ fn generate_allows_no_output() {
 fn generate_allows_null_state() {
     let actual = nu!(pipeline(
         r#"
-        generate 0 {|x|
+        generate {|x|
           if $x == null {
             {out: "done"}
           } else if $x < 1 {
@@ -60,7 +60,7 @@ fn generate_allows_null_state() {
           } else {
             {out: "stopping", next: null}
           }
-        } | to nuon
+        } 0 | to nuon
       "#
     ));
 
@@ -71,7 +71,42 @@ fn generate_allows_null_state() {
 fn generate_allows_null_output() {
     let actual = nu!(pipeline(
         r#"
-        generate 0 {|x|
+        generate {|x|
+          if $x == 3 {
+            {out: "done"}
+          } else {
+            {out: null, next: ($x + 1)}
+          }
+        } 0 | to nuon
+      "#
+    ));
+
+    assert_eq!(actual.out, "[null, null, null, done]");
+}
+
+#[test]
+fn generate_disallows_extra_keys() {
+    let actual = nu!("generate {|x| {foo: bar, out: $x}} 0 ");
+    assert!(actual.err.contains("Invalid block return"));
+}
+
+#[test]
+fn generate_disallows_list() {
+    let actual = nu!("generate {|x| [$x, ($x + 1)]} 0 ");
+    assert!(actual.err.contains("Invalid block return"));
+}
+
+#[test]
+fn generate_disallows_primitive() {
+    let actual = nu!("generate {|x| 1} 0");
+    assert!(actual.err.contains("Invalid block return"));
+}
+
+#[test]
+fn generate_allow_default_parameter() {
+    let actual = nu!(pipeline(
+        r#"
+        generate {|x = 0|
           if $x == 3 {
             {out: "done"}
           } else {
@@ -82,22 +117,34 @@ fn generate_allows_null_output() {
     ));
 
     assert_eq!(actual.out, "[null, null, null, done]");
+
+    // if initial is given, use initial value
+    let actual = nu!(pipeline(
+        r#"
+        generate {|x = 0|
+          if $x == 3 {
+            {out: "done"}
+          } else {
+            {out: null, next: ($x + 1)}
+          }
+        } 1 | to nuon
+      "#
+    ));
+    assert_eq!(actual.out, "[null, null, done]");
 }
 
 #[test]
-fn generate_disallows_extra_keys() {
+fn generate_raise_error_on_no_default_parameter_closure_and_init_val() {
-    let actual = nu!("generate 0 {|x| {foo: bar, out: $x}}");
+    let actual = nu!(pipeline(
-    assert!(actual.err.contains("Invalid block return"));
+        r#"
-}
+        generate {|x|
-
+          if $x == 3 {
-#[test]
+            {out: "done"}
-fn generate_disallows_list() {
+          } else {
-    let actual = nu!("generate 0 {|x| [$x, ($x + 1)]}");
+            {out: null, next: ($x + 1)}
-    assert!(actual.err.contains("Invalid block return"));
+          }
-}
+        } | to nuon
-
+      "#
-#[test]
+    ));
-fn generate_disallows_primitive() {
+    assert!(actual.err.contains("The initial value is missing"));
-    let actual = nu!("generate 0 {|x| 1}");
-    assert!(actual.err.contains("Invalid block return"));
 }

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

@@ -115,6 +115,7 @@ mod try_;
 mod ucp;
 #[cfg(unix)]
 mod ulimit;
+mod window;
 
 mod debug;
 mod umkdir;

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

@@ -439,3 +439,37 @@ fn no_duplicate_redirection() {
         );
     });
 }
+
+#[rstest::rstest]
+#[case("let", "out>")]
+#[case("let", "err>")]
+#[case("let", "out+err>")]
+#[case("mut", "out>")]
+#[case("mut", "err>")]
+#[case("mut", "out+err>")]
+fn file_redirection_in_let_and_mut(#[case] keyword: &str, #[case] redir: &str) {
+    Playground::setup("file redirection in let and mut", |dirs, _| {
+        let actual = nu!(
+            cwd: dirs.test(),
+            format!("$env.BAZ = 'foo'; {keyword} v = nu --testbin echo_env_mixed out-err BAZ BAZ {redir} result.txt")
+        );
+        assert!(actual.status.success());
+        assert!(file_contents(dirs.test().join("result.txt")).contains("foo"));
+    })
+}
+
+#[rstest::rstest]
+#[case("let", "err>|", "foo3")]
+#[case("let", "out+err>|", "7")]
+#[case("mut", "err>|", "foo3")]
+#[case("mut", "out+err>|", "7")]
+fn pipe_redirection_in_let_and_mut(
+    #[case] keyword: &str,
+    #[case] redir: &str,
+    #[case] output: &str,
+) {
+    let actual = nu!(
+        format!("$env.BAZ = 'foo'; {keyword} v = nu --testbin echo_env_mixed out-err BAZ BAZ {redir} str length; $v")
+    );
+    assert_eq!(actual.out, output);
+}

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

@@ -0,0 +1,103 @@
+use nu_test_support::nu;
+
+#[test]
+fn window_size_negative() {
+    let actual = nu!("[0 1 2] | window -1");
+    assert!(actual.err.contains("positive"));
+}
+
+#[test]
+fn window_size_zero() {
+    let actual = nu!("[0 1 2] | window 0");
+    assert!(actual.err.contains("zero"));
+}
+
+#[test]
+fn window_size_not_int() {
+    let actual = nu!("[0 1 2] | window (if true { 1sec })");
+    assert!(actual.err.contains("can't convert"));
+}
+
+#[test]
+fn stride_negative() {
+    let actual = nu!("[0 1 2] | window 1 -s -1");
+    assert!(actual.err.contains("positive"));
+}
+
+#[test]
+fn stride_zero() {
+    let actual = nu!("[0 1 2] | window 1 -s 0");
+    assert!(actual.err.contains("zero"));
+}
+
+#[test]
+fn stride_not_int() {
+    let actual = nu!("[0 1 2] | window 1 -s (if true { 1sec })");
+    assert!(actual.err.contains("can't convert"));
+}
+
+#[test]
+fn empty() {
+    let actual = nu!("[] | window 2 | is-empty");
+    assert_eq!(actual.out, "true");
+}
+
+#[test]
+fn list_stream() {
+    let actual = nu!("([0 1 2] | every 1 | window 2) == ([0 1 2] | window 2)");
+    assert_eq!(actual.out, "true");
+}
+
+#[test]
+fn table_stream() {
+    let actual = nu!("([[foo bar]; [0 1] [2 3] [4 5]] | every 1 | window 2) == ([[foo bar]; [0 1] [2 3] [4 5]] | window 2)");
+    assert_eq!(actual.out, "true");
+}
+
+#[test]
+fn no_empty_chunks() {
+    let actual = nu!("([0 1 2 3 4 5] | window 3 -s 3 -r | length) == 2");
+    assert_eq!(actual.out, "true");
+}
+
+#[test]
+fn same_as_chunks() {
+    let actual = nu!("([0 1 2 3 4] | window 2 -s 2 -r) == ([0 1 2 3 4 ] | chunks 2)");
+    assert_eq!(actual.out, "true");
+}
+
+#[test]
+fn stride_equal_to_window_size() {
+    let actual = nu!("([0 1 2 3] | window 2 -s 2 | flatten) == [0 1 2 3]");
+    assert_eq!(actual.out, "true");
+}
+
+#[test]
+fn stride_greater_than_window_size() {
+    let actual = nu!("([0 1 2 3 4] | window 2 -s 3 | flatten) == [0 1 3 4]");
+    assert_eq!(actual.out, "true");
+}
+
+#[test]
+fn stride_less_than_window_size() {
+    let actual = nu!("([0 1 2 3 4 5] | window 3 -s 2 | length) == 2");
+    assert_eq!(actual.out, "true");
+}
+
+#[test]
+fn stride_equal_to_window_size_remainder() {
+    let actual = nu!("([0 1 2 3 4] | window 2 -s 2 -r | flatten) == [0 1 2 3 4]");
+    assert_eq!(actual.out, "true");
+}
+
+#[test]
+fn stride_greater_than_window_size_remainder() {
+    let actual = nu!("([0 1 2 3 4] | window 2 -s 3 -r | flatten) == [0 1 3 4]");
+    assert_eq!(actual.out, "true");
+}
+
+#[test]
+fn stride_less_than_window_size_remainder() {
+    let actual = nu!("([0 1 2 3 4 5] | window 3 -s 2 -r | length) == 3");
+    assert_eq!(actual.out, "true");
+}

crates/nu-engine/src/compile/builder.rs

@@ -204,6 +204,7 @@ impl BlockBuilder {
             Instruction::Drain { src } => allocate(&[*src], &[]),
             Instruction::LoadVariable { dst, var_id: _ } => allocate(&[], &[*dst]),
             Instruction::StoreVariable { var_id: _, src } => allocate(&[*src], &[]),
+            Instruction::DropVariable { var_id: _ } => Ok(()),
             Instruction::LoadEnv { dst, key: _ } => allocate(&[], &[*dst]),
             Instruction::LoadEnvOpt { dst, key: _ } => allocate(&[], &[*dst]),
             Instruction::StoreEnv { key: _, src } => allocate(&[*src], &[]),

crates/nu-engine/src/compile/expression.rs

@@ -171,6 +171,27 @@ pub(crate) fn compile_expression(
                 Err(CompileError::UnsupportedOperatorExpression { span: op.span })
             }
         }
+        Expr::Collect(var_id, expr) => {
+            let store_reg = if let Some(in_reg) = in_reg {
+                // Collect, clone, store
+                builder.push(Instruction::Collect { src_dst: in_reg }.into_spanned(expr.span))?;
+                builder.clone_reg(in_reg, expr.span)?
+            } else {
+                // Just store nothing in the variable
+                builder.literal(Literal::Nothing.into_spanned(Span::unknown()))?
+            };
+            builder.push(
+                Instruction::StoreVariable {
+                    var_id: *var_id,
+                    src: store_reg,
+                }
+                .into_spanned(expr.span),
+            )?;
+            compile_expression(working_set, builder, expr, redirect_modes, in_reg, out_reg)?;
+            // Clean it up afterward
+            builder.push(Instruction::DropVariable { var_id: *var_id }.into_spanned(expr.span))?;
+            Ok(())
+        }
         Expr::Subexpression(block_id) => {
             let block = working_set.get_block(*block_id);
             compile_block(working_set, builder, block, redirect_modes, in_reg, out_reg)

crates/nu-engine/src/eval.rs

@@ -10,8 +10,8 @@ use nu_protocol::{
     debugger::DebugContext,
     engine::{Closure, EngineState, Redirection, Stack, StateWorkingSet},
     eval_base::Eval,
-    ByteStreamSource, Config, FromValue, IntoPipelineData, OutDest, PipelineData, ShellError, Span,
+    ByteStreamSource, Config, DataSource, FromValue, IntoPipelineData, OutDest, PipelineData,
-    Spanned, Type, Value, VarId, ENV_VARIABLE_ID,
+    PipelineMetadata, ShellError, Span, Spanned, Type, Value, VarId, ENV_VARIABLE_ID,
 };
 use nu_utils::IgnoreCaseExt;
 use std::{fs::OpenOptions, path::PathBuf, sync::Arc};
@@ -259,6 +259,10 @@ pub fn eval_expression_with_input<D: DebugContext>(
             input = eval_external(engine_state, stack, head, args, input)?;
         }
 
+        Expr::Collect(var_id, expr) => {
+            input = eval_collect::<D>(engine_state, stack, *var_id, expr, input)?;
+        }
+
         Expr::Subexpression(block_id) => {
             let block = engine_state.get_block(*block_id);
             // FIXME: protect this collect with ctrl-c
@@ -605,6 +609,44 @@ pub fn eval_block<D: DebugContext>(
     Ok(input)
 }
 
+pub fn eval_collect<D: DebugContext>(
+    engine_state: &EngineState,
+    stack: &mut Stack,
+    var_id: VarId,
+    expr: &Expression,
+    input: PipelineData,
+) -> Result<PipelineData, ShellError> {
+    // Evaluate the expression with the variable set to the collected input
+    let span = input.span().unwrap_or(Span::unknown());
+
+    let metadata = match input.metadata() {
+        // Remove the `FilePath` metadata, because after `collect` it's no longer necessary to
+        // check where some input came from.
+        Some(PipelineMetadata {
+            data_source: DataSource::FilePath(_),
+            content_type: None,
+        }) => None,
+        other => other,
+    };
+
+    let input = input.into_value(span)?;
+
+    stack.add_var(var_id, input.clone());
+
+    let result = eval_expression_with_input::<D>(
+        engine_state,
+        stack,
+        expr,
+        // We still have to pass it as input
+        input.into_pipeline_data_with_metadata(metadata),
+    )
+    .map(|(result, _failed)| result);
+
+    stack.remove_var(var_id);
+
+    result
+}
+
 pub fn eval_subexpression<D: DebugContext>(
     engine_state: &EngineState,
     stack: &mut Stack,
@@ -729,6 +771,18 @@ impl Eval for EvalRuntime {
         eval_external(engine_state, stack, head, args, PipelineData::empty())?.into_value(span)
     }
 
+    fn eval_collect<D: DebugContext>(
+        engine_state: &EngineState,
+        stack: &mut Stack,
+        var_id: VarId,
+        expr: &Expression,
+    ) -> Result<Value, ShellError> {
+        // It's a little bizarre, but the expression can still have some kind of result even with
+        // nothing input
+        eval_collect::<D>(engine_state, stack, var_id, expr, PipelineData::empty())?
+            .into_value(expr.span)
+    }
+
     fn eval_subexpression<D: DebugContext>(
         engine_state: &EngineState,
         stack: &mut Stack,

crates/nu-engine/src/eval_ir.rs

@@ -6,9 +6,9 @@ use nu_protocol::{
     debugger::DebugContext,
     engine::{Argument, Closure, EngineState, ErrorHandler, Matcher, Redirection, Stack},
     ir::{Call, DataSlice, Instruction, IrAstRef, IrBlock, Literal, RedirectMode},
-    record, ByteStreamSource, DeclId, ErrSpan, Flag, IntoPipelineData, IntoSpanned, ListStream,
+    record, ByteStreamSource, DataSource, DeclId, ErrSpan, Flag, IntoPipelineData, IntoSpanned,
-    OutDest, PipelineData, PositionalArg, Range, Record, RegId, ShellError, Signals, Signature,
+    ListStream, OutDest, PipelineData, PipelineMetadata, PositionalArg, Range, Record, RegId,
-    Span, Spanned, Type, Value, VarId, ENV_VARIABLE_ID,
+    ShellError, Signals, Signature, Span, Spanned, Type, Value, VarId, ENV_VARIABLE_ID,
 };
 use nu_utils::IgnoreCaseExt;
 
@@ -345,6 +345,10 @@ fn eval_instruction<D: DebugContext>(
             ctx.stack.add_var(*var_id, value);
             Ok(Continue)
         }
+        Instruction::DropVariable { var_id } => {
+            ctx.stack.remove_var(*var_id);
+            Ok(Continue)
+        }
         Instruction::LoadEnv { dst, key } => {
             let key = ctx.get_str(*key, *span)?;
             if let Some(value) = get_env_var_case_insensitive(ctx, key) {
@@ -1341,9 +1345,19 @@ fn get_env_var_name_case_insensitive<'a>(ctx: &mut EvalContext<'_>, key: &'a str
 }
 
 /// Helper to collect values into [`PipelineData`], preserving original span and metadata
+///
+/// The metadata is removed if it is the file data source, as that's just meant to mark streams.
 fn collect(data: PipelineData, fallback_span: Span) -> Result<PipelineData, ShellError> {
     let span = data.span().unwrap_or(fallback_span);
-    let metadata = data.metadata();
+    let metadata = match data.metadata() {
+        // Remove the `FilePath` metadata, because after `collect` it's no longer necessary to
+        // check where some input came from.
+        Some(PipelineMetadata {
+            data_source: DataSource::FilePath(_),
+            content_type: None,
+        }) => None,
+        other => other,
+    };
     let value = data.into_value(span)?;
     Ok(PipelineData::Value(value, metadata))
 }

crates/nu-parser/src/flatten.rs

@@ -5,7 +5,7 @@ use nu_protocol::{
         RecordItem,
     },
     engine::StateWorkingSet,
-    DeclId, Span, VarId,
+    DeclId, Span, SyntaxShape, VarId,
 };
 use std::fmt::{Display, Formatter, Result};
 
@@ -166,6 +166,22 @@ fn flatten_pipeline_element_into(
     }
 }
 
+fn flatten_positional_arg_into(
+    working_set: &StateWorkingSet,
+    positional: &Expression,
+    shape: &SyntaxShape,
+    output: &mut Vec<(Span, FlatShape)>,
+) {
+    if matches!(shape, SyntaxShape::ExternalArgument)
+        && matches!(positional.expr, Expr::String(..) | Expr::GlobPattern(..))
+    {
+        // Make known external arguments look more like external arguments
+        output.push((positional.span, FlatShape::ExternalArg));
+    } else {
+        flatten_expression_into(working_set, positional, output)
+    }
+}
+
 fn flatten_expression_into(
     working_set: &StateWorkingSet,
     expr: &Expression,
@@ -189,6 +205,9 @@ fn flatten_expression_into(
             ));
             flatten_expression_into(working_set, not, output);
         }
+        Expr::Collect(_, expr) => {
+            flatten_expression_into(working_set, expr, output);
+        }
         Expr::Closure(block_id) => {
             let outer_span = expr.span;
 
@@ -246,16 +265,40 @@ fn flatten_expression_into(
             }
         }
         Expr::Call(call) => {
+            let decl = working_set.get_decl(call.decl_id);
+
             if call.head.end != 0 {
                 // Make sure we don't push synthetic calls
                 output.push((call.head, FlatShape::InternalCall(call.decl_id)));
             }
 
+            // Follow positional arguments from the signature.
+            let signature = decl.signature();
+            let mut positional_args = signature
+                .required_positional
+                .iter()
+                .chain(&signature.optional_positional);
+
             let arg_start = output.len();
             for arg in &call.arguments {
                 match arg {
-                    Argument::Positional(positional) | Argument::Unknown(positional) => {
+                    Argument::Positional(positional) => {
-                        flatten_expression_into(working_set, positional, output)
+                        let positional_arg = positional_args.next();
+                        let shape = positional_arg
+                            .or(signature.rest_positional.as_ref())
+                            .map(|arg| &arg.shape)
+                            .unwrap_or(&SyntaxShape::Any);
+
+                        flatten_positional_arg_into(working_set, positional, shape, output)
+                    }
+                    Argument::Unknown(positional) => {
+                        let shape = signature
+                            .rest_positional
+                            .as_ref()
+                            .map(|arg| &arg.shape)
+                            .unwrap_or(&SyntaxShape::Any);
+
+                        flatten_positional_arg_into(working_set, positional, shape, output)
                     }
                     Argument::Named(named) => {
                         if named.0.span.end != 0 {

crates/nu-parser/src/lite_parser.rs

@@ -2,6 +2,7 @@
 //! can be parsed.
 
 use crate::{Token, TokenContents};
+use itertools::{Either, Itertools};
 use nu_protocol::{ast::RedirectionSource, ParseError, Span};
 use std::mem;
 
@@ -24,6 +25,15 @@ impl LiteRedirectionTarget {
             | LiteRedirectionTarget::Pipe { connector } => *connector,
         }
     }
+
+    pub fn spans(&self) -> impl Iterator<Item = Span> {
+        match *self {
+            LiteRedirectionTarget::File {
+                connector, file, ..
+            } => Either::Left([connector, file].into_iter()),
+            LiteRedirectionTarget::Pipe { connector } => Either::Right(std::iter::once(connector)),
+        }
+    }
 }
 
 #[derive(Debug, Clone)]
@@ -38,6 +48,17 @@ pub enum LiteRedirection {
     },
 }
 
+impl LiteRedirection {
+    pub fn spans(&self) -> impl Iterator<Item = Span> {
+        match self {
+            LiteRedirection::Single { target, .. } => Either::Left(target.spans()),
+            LiteRedirection::Separate { out, err } => {
+                Either::Right(out.spans().chain(err.spans()).sorted())
+            }
+        }
+    }
+}
+
 #[derive(Debug, Clone, Default)]
 pub struct LiteCommand {
     pub pipe: Option<Span>,
@@ -113,6 +134,14 @@ impl LiteCommand {
 
         Ok(())
     }
+
+    pub fn parts_including_redirection(&self) -> impl Iterator<Item = Span> + '_ {
+        self.parts.iter().copied().chain(
+            self.redirection
+                .iter()
+                .flat_map(|redirection| redirection.spans()),
+        )
+    }
 }
 
 #[derive(Debug, Clone, Default)]

crates/nu-parser/src/parse_keywords.rs

@@ -783,6 +783,16 @@ pub fn parse_extern(
                         working_set.get_block_mut(block_id).signature = signature;
                     }
                 } else {
+                    if signature.rest_positional.is_none() {
+                        // Make sure that a known external takes rest args with ExternalArgument
+                        // shape
+                        *signature = signature.rest(
+                            "args",
+                            SyntaxShape::ExternalArgument,
+                            "all other arguments to the command",
+                        );
+                    }
+
                     let decl = KnownExternal {
                         name: external_name,
                         usage,

crates/nu-parser/src/parser.rs

@@ -221,6 +221,22 @@ pub(crate) fn check_call(
     }
 }
 
+/// Parses an unknown argument for the given signature. This handles the parsing as appropriate to
+/// the rest type of the command.
+fn parse_unknown_arg(
+    working_set: &mut StateWorkingSet,
+    span: Span,
+    signature: &Signature,
+) -> Expression {
+    let shape = signature
+        .rest_positional
+        .as_ref()
+        .map(|arg| arg.shape.clone())
+        .unwrap_or(SyntaxShape::Any);
+
+    parse_value(working_set, span, &shape)
+}
+
 /// Parses a string in the arg or head position of an external call.
 ///
 /// If the string begins with `r#`, it is parsed as a raw string. If it doesn't contain any quotes
@@ -427,11 +443,7 @@ fn parse_external_string(working_set: &mut StateWorkingSet, span: Span) -> Expre
 fn parse_external_arg(working_set: &mut StateWorkingSet, span: Span) -> ExternalArgument {
     let contents = working_set.get_span_contents(span);
 
-    if contents.starts_with(b"$") || contents.starts_with(b"(") {
+    if contents.len() > 3
-        ExternalArgument::Regular(parse_dollar_expr(working_set, span))
-    } else if contents.starts_with(b"[") {
-        ExternalArgument::Regular(parse_list_expression(working_set, span, &SyntaxShape::Any))
-    } else if contents.len() > 3
         && contents.starts_with(b"...")
         && (contents[3] == b'$' || contents[3] == b'[' || contents[3] == b'(')
     {
@@ -441,7 +453,19 @@ fn parse_external_arg(working_set: &mut StateWorkingSet, span: Span) -> External
             &SyntaxShape::List(Box::new(SyntaxShape::Any)),
         ))
     } else {
-        ExternalArgument::Regular(parse_external_string(working_set, span))
+        ExternalArgument::Regular(parse_regular_external_arg(working_set, span))
+    }
+}
+
+fn parse_regular_external_arg(working_set: &mut StateWorkingSet, span: Span) -> Expression {
+    let contents = working_set.get_span_contents(span);
+
+    if contents.starts_with(b"$") || contents.starts_with(b"(") {
+        parse_dollar_expr(working_set, span)
+    } else if contents.starts_with(b"[") {
+        parse_list_expression(working_set, span, &SyntaxShape::Any)
+    } else {
+        parse_external_string(working_set, span)
     }
 }
 
@@ -998,7 +1022,7 @@ pub fn parse_internal_call(
                 && signature.allows_unknown_args
             {
                 working_set.parse_errors.truncate(starting_error_count);
-                let arg = parse_value(working_set, arg_span, &SyntaxShape::Any);
+                let arg = parse_unknown_arg(working_set, arg_span, &signature);
 
                 call.add_unknown(arg);
             } else {
@@ -1040,7 +1064,7 @@ pub fn parse_internal_call(
                 && signature.allows_unknown_args
             {
                 working_set.parse_errors.truncate(starting_error_count);
-                let arg = parse_value(working_set, arg_span, &SyntaxShape::Any);
+                let arg = parse_unknown_arg(working_set, arg_span, &signature);
 
                 call.add_unknown(arg);
             } else {
@@ -1135,6 +1159,10 @@ pub fn parse_internal_call(
                     call.add_positional(Expression::garbage(working_set, arg_span));
                 } else {
                     let rest_shape = match &signature.rest_positional {
+                        Some(arg) if matches!(arg.shape, SyntaxShape::ExternalArgument) => {
+                            // External args aren't parsed inside lists in spread position.
+                            SyntaxShape::Any
+                        }
                         Some(arg) => arg.shape.clone(),
                         None => SyntaxShape::Any,
                     };
@@ -1196,7 +1224,7 @@ pub fn parse_internal_call(
             call.add_positional(arg);
             positional_idx += 1;
         } else if signature.allows_unknown_args {
-            let arg = parse_value(working_set, arg_span, &SyntaxShape::Any);
+            let arg = parse_unknown_arg(working_set, arg_span, &signature);
 
             call.add_unknown(arg);
         } else {
@@ -4670,7 +4698,8 @@ pub fn parse_value(
             | SyntaxShape::Signature
             | SyntaxShape::Filepath
             | SyntaxShape::String
-            | SyntaxShape::GlobPattern => {}
+            | SyntaxShape::GlobPattern
+            | SyntaxShape::ExternalArgument => {}
             _ => {
                 working_set.error(ParseError::Expected("non-[] value", span));
                 return Expression::garbage(working_set, span);
@@ -4747,6 +4776,8 @@ pub fn parse_value(
             Expression::garbage(working_set, span)
         }
 
+        SyntaxShape::ExternalArgument => parse_regular_external_arg(working_set, span),
+
         SyntaxShape::Any => {
             if bytes.starts_with(b"[") {
                 //parse_value(working_set, span, &SyntaxShape::Table)
@@ -5299,6 +5330,7 @@ pub fn parse_expression(working_set: &mut StateWorkingSet, spans: &[Span]) -> Ex
             let mut block = Block::default();
             let ty = output.ty.clone();
             block.pipelines = vec![Pipeline::from_vec(vec![output])];
+            block.span = Some(Span::concat(spans));
 
             compile_block(working_set, &mut block);
 
@@ -5393,9 +5425,19 @@ pub fn parse_builtin_commands(
     match name {
         b"def" => parse_def(working_set, lite_command, None).0,
         b"extern" => parse_extern(working_set, lite_command, None),
-        b"let" => parse_let(working_set, &lite_command.parts),
+        b"let" => parse_let(
+            working_set,
+            &lite_command
+                .parts_including_redirection()
+                .collect::<Vec<Span>>(),
+        ),
         b"const" => parse_const(working_set, &lite_command.parts),
-        b"mut" => parse_mut(working_set, &lite_command.parts),
+        b"mut" => parse_mut(
+            working_set,
+            &lite_command
+                .parts_including_redirection()
+                .collect::<Vec<Span>>(),
+        ),
         b"for" => {
             let expr = parse_for(working_set, lite_command);
             Pipeline::from_vec(vec![expr])
@@ -5647,169 +5689,73 @@ pub(crate) fn redirecting_builtin_error(
     }
 }
 
-pub fn parse_pipeline(
+pub fn parse_pipeline(working_set: &mut StateWorkingSet, pipeline: &LitePipeline) -> Pipeline {
-    working_set: &mut StateWorkingSet,
+    let first_command = pipeline.commands.first();
-    pipeline: &LitePipeline,
+    let first_command_name = first_command
-    is_subexpression: bool,
+        .and_then(|command| command.parts.first())
-    pipeline_index: usize,
+        .map(|span| working_set.get_span_contents(*span));
-) -> Pipeline {
+
     if pipeline.commands.len() > 1 {
-        // Special case: allow `let` and `mut` to consume the whole pipeline, eg) `let abc = "foo" | str length`
+        // Special case: allow "let" or "mut" to consume the whole pipeline, if this is a pipeline
-        if let Some(&first) = pipeline.commands[0].parts.first() {
+        // with multiple commands
-            let first = working_set.get_span_contents(first);
+        if matches!(first_command_name, Some(b"let" | b"mut")) {
-            if first == b"let" || first == b"mut" {
+            // Merge the pipeline into one command
-                let name = if first == b"let" { "let" } else { "mut" };
+            let first_command = first_command.expect("must be Some");
-                let mut new_command = LiteCommand {
-                    comments: vec![],
-                    parts: pipeline.commands[0].parts.clone(),
-                    pipe: None,
-                    redirection: None,
-                };
 
-                if let Some(redirection) = pipeline.commands[0].redirection.as_ref() {
+            let remainder_span = first_command
-                    working_set.error(redirecting_builtin_error(name, redirection));
+                .parts_including_redirection()
-                }
+                .skip(3)
+                .chain(
+                    pipeline.commands[1..]
+                        .iter()
+                        .flat_map(|command| command.parts_including_redirection()),
+                )
+                .reduce(Span::append);
 
-                for element in &pipeline.commands[1..] {
+            let parts = first_command
-                    if let Some(redirection) = pipeline.commands[0].redirection.as_ref() {
+                .parts
-                        working_set.error(redirecting_builtin_error(name, redirection));
+                .iter()
-                    } else {
+                .take(3) // the let/mut start itself
-                        new_command.parts.push(element.pipe.expect("pipe span"));
+                .copied()
-                        new_command.comments.extend_from_slice(&element.comments);
+                .chain(remainder_span) // everything else
-                        new_command.parts.extend_from_slice(&element.parts);
+                .collect();
-                    }
-                }
 
-                // if the 'let' is complete enough, use it, if not, fall through for now
+            let comments = pipeline
-                if new_command.parts.len() > 3 {
+                .commands
-                    let rhs_span = Span::concat(&new_command.parts[3..]);
+                .iter()
+                .flat_map(|command| command.comments.iter())
+                .copied()
+                .collect();
 
-                    new_command.parts.truncate(3);
+            let new_command = LiteCommand {
-                    new_command.parts.push(rhs_span);
+                pipe: None,
-
+                comments,
-                    let mut pipeline = parse_builtin_commands(working_set, &new_command);
+                parts,
-
+                redirection: None,
-                    if pipeline_index == 0 {
+            };
-                        let let_decl_id = working_set.find_decl(b"let");
+            parse_builtin_commands(working_set, &new_command)
-                        let mut_decl_id = working_set.find_decl(b"mut");
-                        for element in pipeline.elements.iter_mut() {
-                            if let Expr::Call(call) = &element.expr.expr {
-                                if Some(call.decl_id) == let_decl_id
-                                    || Some(call.decl_id) == mut_decl_id
-                                {
-                                    // Do an expansion
-                                    if let Some(Expression {
-                                        expr: Expr::Block(block_id),
-                                        ..
-                                    }) = call.positional_iter().nth(1)
-                                    {
-                                        let block = working_set.get_block(*block_id);
-
-                                        if let Some(element) = block
-                                            .pipelines
-                                            .first()
-                                            .and_then(|p| p.elements.first())
-                                            .cloned()
-                                        {
-                                            if element.has_in_variable(working_set) {
-                                                let element = wrap_element_with_collect(
-                                                    working_set,
-                                                    &element,
-                                                );
-                                                let block = working_set.get_block_mut(*block_id);
-                                                block.pipelines[0].elements[0] = element;
-                                            }
-                                        }
-                                    }
-                                    continue;
-                                } else if element.has_in_variable(working_set) && !is_subexpression
-                                {
-                                    *element = wrap_element_with_collect(working_set, element);
-                                }
-                            } else if element.has_in_variable(working_set) && !is_subexpression {
-                                *element = wrap_element_with_collect(working_set, element);
-                            }
-                        }
-                    }
-
-                    return pipeline;
-                }
-            }
-        }
-
-        let mut elements = pipeline
-            .commands
-            .iter()
-            .map(|element| parse_pipeline_element(working_set, element))
-            .collect::<Vec<_>>();
-
-        if is_subexpression {
-            for element in elements.iter_mut().skip(1) {
-                if element.has_in_variable(working_set) {
-                    *element = wrap_element_with_collect(working_set, element);
-                }
-            }
         } else {
-            for element in elements.iter_mut() {
+            // Parse a normal multi command pipeline
-                if element.has_in_variable(working_set) {
+            let elements: Vec<_> = pipeline
-                    *element = wrap_element_with_collect(working_set, element);
+                .commands
-                }
+                .iter()
-            }
+                .enumerate()
-        }
+                .map(|(index, element)| {
-
+                    let element = parse_pipeline_element(working_set, element);
-        Pipeline { elements }
+                    // Handle $in for pipeline elements beyond the first one
-    } else {
+                    if index > 0 && element.has_in_variable(working_set) {
-        if let Some(&first) = pipeline.commands[0].parts.first() {
+                        wrap_element_with_collect(working_set, element.clone())
-            let first = working_set.get_span_contents(first);
+                    } else {
-            if first == b"let" || first == b"mut" {
+                        element
-                if let Some(redirection) = pipeline.commands[0].redirection.as_ref() {
-                    let name = if first == b"let" { "let" } else { "mut" };
-                    working_set.error(redirecting_builtin_error(name, redirection));
-                }
-            }
-        }
-
-        let mut pipeline = parse_builtin_commands(working_set, &pipeline.commands[0]);
-
-        let let_decl_id = working_set.find_decl(b"let");
-        let mut_decl_id = working_set.find_decl(b"mut");
-
-        if pipeline_index == 0 {
-            for element in pipeline.elements.iter_mut() {
-                if let Expr::Call(call) = &element.expr.expr {
-                    if Some(call.decl_id) == let_decl_id || Some(call.decl_id) == mut_decl_id {
-                        // Do an expansion
-                        if let Some(Expression {
-                            expr: Expr::Block(block_id),
-                            ..
-                        }) = call.positional_iter().nth(1)
-                        {
-                            let block = working_set.get_block(*block_id);
-
-                            if let Some(element) = block
-                                .pipelines
-                                .first()
-                                .and_then(|p| p.elements.first())
-                                .cloned()
-                            {
-                                if element.has_in_variable(working_set) {
-                                    let element = wrap_element_with_collect(working_set, &element);
-                                    let block = working_set.get_block_mut(*block_id);
-                                    block.pipelines[0].elements[0] = element;
-                                }
-                            }
-                        }
-                        continue;
-                    } else if element.has_in_variable(working_set) && !is_subexpression {
-                        *element = wrap_element_with_collect(working_set, element);
                     }
-                } else if element.has_in_variable(working_set) && !is_subexpression {
+                })
-                    *element = wrap_element_with_collect(working_set, element);
+                .collect();
-                }
-            }
-        }
 
-        pipeline
+            Pipeline { elements }
+        }
+    } else {
+        // If there's only one command in the pipeline, this could be a builtin command
+        parse_builtin_commands(working_set, &pipeline.commands[0])
     }
 }
 
@@ -5840,18 +5786,45 @@ pub fn parse_block(
     }
 
     let mut block = Block::new_with_capacity(lite_block.block.len());
+    block.span = Some(span);
 
-    for (idx, lite_pipeline) in lite_block.block.iter().enumerate() {
+    for lite_pipeline in &lite_block.block {
-        let pipeline = parse_pipeline(working_set, lite_pipeline, is_subexpression, idx);
+        let pipeline = parse_pipeline(working_set, lite_pipeline);
         block.pipelines.push(pipeline);
     }
 
+    // If this is not a subexpression and there are any pipelines where the first element has $in,
+    // we can wrap the whole block in collect so that they all reference the same $in
+    if !is_subexpression
+        && block
+            .pipelines
+            .iter()
+            .flat_map(|pipeline| pipeline.elements.first())
+            .any(|element| element.has_in_variable(working_set))
+    {
+        // Move the block out to prepare it to become a subexpression
+        let inner_block = std::mem::take(&mut block);
+        block.span = inner_block.span;
+        let ty = inner_block.output_type();
+        let block_id = working_set.add_block(Arc::new(inner_block));
+
+        // Now wrap it in a Collect expression, and put it in the block as the only pipeline
+        let subexpression = Expression::new(working_set, Expr::Subexpression(block_id), span, ty);
+        let collect = wrap_expr_with_collect(working_set, subexpression);
+
+        block.pipelines.push(Pipeline {
+            elements: vec![PipelineElement {
+                pipe: None,
+                expr: collect,
+                redirection: None,
+            }],
+        });
+    }
+
     if scoped {
         working_set.exit_scope();
     }
 
-    block.span = Some(span);
-
     let errors = type_check::check_block_input_output(working_set, &block);
     if !errors.is_empty() {
         working_set.parse_errors.extend_from_slice(&errors);
@@ -6220,6 +6193,10 @@ pub fn discover_captures_in_expr(
                 discover_captures_in_expr(working_set, &match_.1, seen, seen_blocks, output)?;
             }
         }
+        Expr::Collect(var_id, expr) => {
+            seen.push(*var_id);
+            discover_captures_in_expr(working_set, expr, seen, seen_blocks, output)?
+        }
         Expr::RowCondition(block_id) | Expr::Subexpression(block_id) => {
             let block = working_set.get_block(*block_id);
 
@@ -6270,28 +6247,28 @@ pub fn discover_captures_in_expr(
 
 fn wrap_redirection_with_collect(
     working_set: &mut StateWorkingSet,
-    target: &RedirectionTarget,
+    target: RedirectionTarget,
 ) -> RedirectionTarget {
     match target {
         RedirectionTarget::File { expr, append, span } => RedirectionTarget::File {
             expr: wrap_expr_with_collect(working_set, expr),
-            span: *span,
+            span,
-            append: *append,
+            append,
         },
-        RedirectionTarget::Pipe { span } => RedirectionTarget::Pipe { span: *span },
+        RedirectionTarget::Pipe { span } => RedirectionTarget::Pipe { span },
     }
 }
 
 fn wrap_element_with_collect(
     working_set: &mut StateWorkingSet,
-    element: &PipelineElement,
+    element: PipelineElement,
 ) -> PipelineElement {
     PipelineElement {
         pipe: element.pipe,
-        expr: wrap_expr_with_collect(working_set, &element.expr),
+        expr: wrap_expr_with_collect(working_set, element.expr),
-        redirection: element.redirection.as_ref().map(|r| match r {
+        redirection: element.redirection.map(|r| match r {
             PipelineRedirection::Single { source, target } => PipelineRedirection::Single {
-                source: *source,
+                source,
                 target: wrap_redirection_with_collect(working_set, target),
             },
             PipelineRedirection::Separate { out, err } => PipelineRedirection::Separate {
@@ -6302,65 +6279,24 @@ fn wrap_element_with_collect(
     }
 }
 
-fn wrap_expr_with_collect(working_set: &mut StateWorkingSet, expr: &Expression) -> Expression {
+fn wrap_expr_with_collect(working_set: &mut StateWorkingSet, expr: Expression) -> Expression {
     let span = expr.span;
 
-    if let Some(decl_id) = working_set.find_decl(b"collect") {
+    // IN_VARIABLE_ID should get replaced with a unique variable, so that we don't have to
-        let mut output = vec![];
+    // execute as a closure
+    let var_id = working_set.add_variable(b"$in".into(), expr.span, Type::Any, false);
+    let mut expr = expr.clone();
+    expr.replace_in_variable(working_set, var_id);
 
-        let var_id = IN_VARIABLE_ID;
+    // Bind the custom `$in` variable for that particular expression
-        let mut signature = Signature::new("");
+    let ty = expr.ty.clone();
-        signature.required_positional.push(PositionalArg {
+    Expression::new(
-            var_id: Some(var_id),
+        working_set,
-            name: "$in".into(),
+        Expr::Collect(var_id, Box::new(expr)),
-            desc: String::new(),
+        span,
-            shape: SyntaxShape::Any,
+        // We can expect it to have the same result type
-            default_value: None,
+        ty,
-        });
+    )
-
-        let mut block = Block {
-            pipelines: vec![Pipeline::from_vec(vec![expr.clone()])],
-            signature: Box::new(signature),
-            ..Default::default()
-        };
-
-        compile_block(working_set, &mut block);
-
-        let block_id = working_set.add_block(Arc::new(block));
-
-        output.push(Argument::Positional(Expression::new(
-            working_set,
-            Expr::Closure(block_id),
-            span,
-            Type::Any,
-        )));
-
-        output.push(Argument::Named((
-            Spanned {
-                item: "keep-env".to_string(),
-                span: Span::new(0, 0),
-            },
-            None,
-            None,
-        )));
-
-        // The containing, synthetic call to `collect`.
-        // We don't want to have a real span as it will confuse flattening
-        // The args are where we'll get the real info
-        Expression::new(
-            working_set,
-            Expr::Call(Box::new(Call {
-                head: Span::new(0, 0),
-                arguments: output,
-                decl_id,
-                parser_info: HashMap::new(),
-            })),
-            span,
-            Type::Any,
-        )
-    } else {
-        Expression::garbage(working_set, span)
-    }
 }
 
 // Parses a vector of u8 to create an AST Block. If a file name is given, then

crates/nu-parser/tests/test_parser.rs

@@ -41,6 +41,41 @@ impl Command for Let {
     }
 }
 
+#[cfg(test)]
+#[derive(Clone)]
+pub struct Mut;
+
+#[cfg(test)]
+impl Command for Mut {
+    fn name(&self) -> &str {
+        "mut"
+    }
+
+    fn usage(&self) -> &str {
+        "Mock mut command."
+    }
+
+    fn signature(&self) -> nu_protocol::Signature {
+        Signature::build("mut")
+            .required("var_name", SyntaxShape::VarWithOptType, "variable name")
+            .required(
+                "initial_value",
+                SyntaxShape::Keyword(b"=".to_vec(), Box::new(SyntaxShape::MathExpression)),
+                "equals sign followed by value",
+            )
+    }
+
+    fn run(
+        &self,
+        _engine_state: &EngineState,
+        _stack: &mut Stack,
+        _call: &Call,
+        _input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        todo!()
+    }
+}
+
 fn test_int(
     test_tag: &str,     // name of sub-test
     test: &[u8],        // input expression
@@ -1149,11 +1184,29 @@ fn test_nothing_comparison_eq() {
 fn test_redirection_with_letmut(#[case] phase: &[u8]) {
     let engine_state = EngineState::new();
     let mut working_set = StateWorkingSet::new(&engine_state);
-    let _block = parse(&mut working_set, None, phase, true);
+    working_set.add_decl(Box::new(Let));
-    assert!(matches!(
+    working_set.add_decl(Box::new(Mut));
-        working_set.parse_errors.first(),
+
-        Some(ParseError::RedirectingBuiltinCommand(_, _, _))
+    let block = parse(&mut working_set, None, phase, true);
-    ));
+    assert!(
+        working_set.parse_errors.is_empty(),
+        "parse errors: {:?}",
+        working_set.parse_errors
+    );
+    assert_eq!(1, block.pipelines[0].elements.len());
+
+    let element = &block.pipelines[0].elements[0];
+    assert!(element.redirection.is_none()); // it should be in the let block, not here
+
+    if let Expr::Call(call) = &element.expr.expr {
+        let arg = call.positional_nth(1).expect("no positional args");
+        let block_id = arg.as_block().expect("arg 1 is not a block");
+        let block = working_set.get_block(block_id);
+        let inner_element = &block.pipelines[0].elements[0];
+        assert!(inner_element.redirection.is_some());
+    } else {
+        panic!("expected Call: {:?}", block.pipelines[0].elements[0])
+    }
 }
 
 #[rstest]

crates/nu-plugin-engine/src/context.rs

@@ -1,9 +1,10 @@
 use crate::util::MutableCow;
 use nu_engine::{get_eval_block_with_early_return, get_full_help, ClosureEvalOnce};
+use nu_plugin_protocol::EvaluatedCall;
 use nu_protocol::{
     engine::{Call, Closure, EngineState, Redirection, Stack},
-    Config, IntoSpanned, OutDest, PipelineData, PluginIdentity, ShellError, Signals, Span, Spanned,
+    ir, Config, DeclId, IntoSpanned, OutDest, PipelineData, PluginIdentity, ShellError, Signals,
-    Value,
+    Span, Spanned, Value,
 };
 use std::{
     borrow::Cow,
@@ -44,6 +45,17 @@ pub trait PluginExecutionContext: Send + Sync {
         redirect_stdout: bool,
         redirect_stderr: bool,
     ) -> Result<PipelineData, ShellError>;
+    /// Find a declaration by name
+    fn find_decl(&self, name: &str) -> Result<Option<DeclId>, ShellError>;
+    /// Call a declaration with arguments and input
+    fn call_decl(
+        &mut self,
+        decl_id: DeclId,
+        call: EvaluatedCall,
+        input: PipelineData,
+        redirect_stdout: bool,
+        redirect_stderr: bool,
+    ) -> Result<PipelineData, ShellError>;
     /// Create an owned version of the context with `'static` lifetime
     fn boxed(&self) -> Box<dyn PluginExecutionContext>;
 }
@@ -177,19 +189,10 @@ impl<'a> PluginExecutionContext for PluginExecutionCommandContext<'a> {
             .captures_to_stack(closure.item.captures)
             .reset_pipes();
 
-        let stdout = if redirect_stdout {
+        let stack = &mut stack.push_redirection(
-            Some(Redirection::Pipe(OutDest::Capture))
+            redirect_stdout.then_some(Redirection::Pipe(OutDest::Capture)),
-        } else {
+            redirect_stderr.then_some(Redirection::Pipe(OutDest::Capture)),
-            None
+        );
-        };
-
-        let stderr = if redirect_stderr {
-            Some(Redirection::Pipe(OutDest::Capture))
-        } else {
-            None
-        };
-
-        let stack = &mut stack.push_redirection(stdout, stderr);
 
         // Set up the positional arguments
         for (idx, value) in positional.into_iter().enumerate() {
@@ -211,6 +214,57 @@ impl<'a> PluginExecutionContext for PluginExecutionCommandContext<'a> {
         eval_block_with_early_return(&self.engine_state, stack, block, input)
     }
 
+    fn find_decl(&self, name: &str) -> Result<Option<DeclId>, ShellError> {
+        Ok(self.engine_state.find_decl(name.as_bytes(), &[]))
+    }
+
+    fn call_decl(
+        &mut self,
+        decl_id: DeclId,
+        call: EvaluatedCall,
+        input: PipelineData,
+        redirect_stdout: bool,
+        redirect_stderr: bool,
+    ) -> Result<PipelineData, ShellError> {
+        if decl_id >= self.engine_state.num_decls() {
+            return Err(ShellError::GenericError {
+                error: "Plugin misbehaving".into(),
+                msg: format!("Tried to call unknown decl id: {}", decl_id),
+                span: Some(call.head),
+                help: None,
+                inner: vec![],
+            });
+        }
+
+        let decl = self.engine_state.get_decl(decl_id);
+
+        let stack = &mut self.stack.push_redirection(
+            redirect_stdout.then_some(Redirection::Pipe(OutDest::Capture)),
+            redirect_stderr.then_some(Redirection::Pipe(OutDest::Capture)),
+        );
+
+        let mut call_builder = ir::Call::build(decl_id, call.head);
+
+        for positional in call.positional {
+            call_builder.add_positional(stack, positional.span(), positional);
+        }
+
+        for (name, value) in call.named {
+            if let Some(value) = value {
+                call_builder.add_named(stack, &name.item, "", name.span, value);
+            } else {
+                call_builder.add_flag(stack, &name.item, "", name.span);
+            }
+        }
+
+        decl.run(
+            &self.engine_state,
+            stack,
+            &(&call_builder.finish()).into(),
+            input,
+        )
+    }
+
     fn boxed(&self) -> Box<dyn PluginExecutionContext + 'static> {
         Box::new(PluginExecutionCommandContext {
             identity: self.identity.clone(),
@@ -298,6 +352,25 @@ impl PluginExecutionContext for PluginExecutionBogusContext {
         })
     }
 
+    fn find_decl(&self, _name: &str) -> Result<Option<DeclId>, ShellError> {
+        Err(ShellError::NushellFailed {
+            msg: "find_decl not implemented on bogus".into(),
+        })
+    }
+
+    fn call_decl(
+        &mut self,
+        _decl_id: DeclId,
+        _call: EvaluatedCall,
+        _input: PipelineData,
+        _redirect_stdout: bool,
+        _redirect_stderr: bool,
+    ) -> Result<PipelineData, ShellError> {
+        Err(ShellError::NushellFailed {
+            msg: "call_decl not implemented on bogus".into(),
+        })
+    }
+
     fn boxed(&self) -> Box<dyn PluginExecutionContext + 'static> {
         Box::new(PluginExecutionBogusContext)
     }

crates/nu-plugin-engine/src/interface/mod.rs

@@ -1322,6 +1322,22 @@ pub(crate) fn handle_engine_call(
         } => context
             .eval_closure(closure, positional, input, redirect_stdout, redirect_stderr)
             .map(EngineCallResponse::PipelineData),
+        EngineCall::FindDecl(name) => context.find_decl(&name).map(|decl_id| {
+            if let Some(decl_id) = decl_id {
+                EngineCallResponse::Identifier(decl_id)
+            } else {
+                EngineCallResponse::empty()
+            }
+        }),
+        EngineCall::CallDecl {
+            decl_id,
+            call,
+            input,
+            redirect_stdout,
+            redirect_stderr,
+        } => context
+            .call_decl(decl_id, call, input, redirect_stdout, redirect_stderr)
+            .map(EngineCallResponse::PipelineData),
     }
 }
 

crates/nu-plugin-protocol/src/evaluated_call.rs

@@ -27,6 +27,82 @@ pub struct EvaluatedCall {
 }
 
 impl EvaluatedCall {
+    /// Create a new [`EvaluatedCall`] with the given head span.
+    pub fn new(head: Span) -> EvaluatedCall {
+        EvaluatedCall {
+            head,
+            positional: vec![],
+            named: vec![],
+        }
+    }
+
+    /// Add a positional argument to an [`EvaluatedCall`].
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// # use nu_protocol::{Value, Span, IntoSpanned};
+    /// # use nu_plugin_protocol::EvaluatedCall;
+    /// # let head = Span::test_data();
+    /// let mut call = EvaluatedCall::new(head);
+    /// call.add_positional(Value::test_int(1337));
+    /// ```
+    pub fn add_positional(&mut self, value: Value) -> &mut Self {
+        self.positional.push(value);
+        self
+    }
+
+    /// Add a named argument to an [`EvaluatedCall`].
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// # use nu_protocol::{Value, Span, IntoSpanned};
+    /// # use nu_plugin_protocol::EvaluatedCall;
+    /// # let head = Span::test_data();
+    /// let mut call = EvaluatedCall::new(head);
+    /// call.add_named("foo".into_spanned(head), Value::test_string("bar"));
+    /// ```
+    pub fn add_named(&mut self, name: Spanned<impl Into<String>>, value: Value) -> &mut Self {
+        self.named.push((name.map(Into::into), Some(value)));
+        self
+    }
+
+    /// Add a flag argument to an [`EvaluatedCall`]. A flag argument is a named argument with no
+    /// value.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// # use nu_protocol::{Value, Span, IntoSpanned};
+    /// # use nu_plugin_protocol::EvaluatedCall;
+    /// # let head = Span::test_data();
+    /// let mut call = EvaluatedCall::new(head);
+    /// call.add_flag("pretty".into_spanned(head));
+    /// ```
+    pub fn add_flag(&mut self, name: Spanned<impl Into<String>>) -> &mut Self {
+        self.named.push((name.map(Into::into), None));
+        self
+    }
+
+    /// Builder variant of [`.add_positional()`].
+    pub fn with_positional(mut self, value: Value) -> Self {
+        self.add_positional(value);
+        self
+    }
+
+    /// Builder variant of [`.add_named()`].
+    pub fn with_named(mut self, name: Spanned<impl Into<String>>, value: Value) -> Self {
+        self.add_named(name, value);
+        self
+    }
+
+    /// Builder variant of [`.add_flag()`].
+    pub fn with_flag(mut self, name: Spanned<impl Into<String>>) -> Self {
+        self.add_flag(name);
+        self
+    }
+
     /// Try to create an [`EvaluatedCall`] from a command `Call`.
     pub fn try_from_call(
         call: &Call,
@@ -192,6 +268,16 @@ impl EvaluatedCall {
         Ok(false)
     }
 
+    /// Returns the [`Span`] of the name of an optional named argument.
+    ///
+    /// This can be used in errors for named arguments that don't take values.
+    pub fn get_flag_span(&self, flag_name: &str) -> Option<Span> {
+        self.named
+            .iter()
+            .find(|(name, _)| name.item == flag_name)
+            .map(|(name, _)| name.span)
+    }
+
     /// Returns the [`Value`] of an optional named argument
     ///
     /// # Examples

crates/nu-plugin-protocol/src/lib.rs

@@ -22,7 +22,7 @@ mod tests;
 pub mod test_util;
 
 use nu_protocol::{
-    ast::Operator, engine::Closure, ByteStreamType, Config, LabeledError, PipelineData,
+    ast::Operator, engine::Closure, ByteStreamType, Config, DeclId, LabeledError, PipelineData,
     PluginMetadata, PluginSignature, ShellError, Span, Spanned, Value,
 };
 use nu_utils::SharedCow;
@@ -496,6 +496,21 @@ pub enum EngineCall<D> {
         /// Whether to redirect stderr from external commands
         redirect_stderr: bool,
     },
+    /// Find a declaration by name
+    FindDecl(String),
+    /// Call a declaration with args
+    CallDecl {
+        /// The id of the declaration to be called (can be found with `FindDecl`)
+        decl_id: DeclId,
+        /// Information about the call (head span, arguments, etc.)
+        call: EvaluatedCall,
+        /// Pipeline input to the call
+        input: D,
+        /// Whether to redirect stdout from external commands
+        redirect_stdout: bool,
+        /// Whether to redirect stderr from external commands
+        redirect_stderr: bool,
+    },
 }
 
 impl<D> EngineCall<D> {
@@ -513,6 +528,8 @@ impl<D> EngineCall<D> {
             EngineCall::LeaveForeground => "LeaveForeground",
             EngineCall::GetSpanContents(_) => "GetSpanContents",
             EngineCall::EvalClosure { .. } => "EvalClosure",
+            EngineCall::FindDecl(_) => "FindDecl",
+            EngineCall::CallDecl { .. } => "CallDecl",
         }
     }
 
@@ -546,6 +563,20 @@ impl<D> EngineCall<D> {
                 redirect_stdout,
                 redirect_stderr,
             },
+            EngineCall::FindDecl(name) => EngineCall::FindDecl(name),
+            EngineCall::CallDecl {
+                decl_id,
+                call,
+                input,
+                redirect_stdout,
+                redirect_stderr,
+            } => EngineCall::CallDecl {
+                decl_id,
+                call,
+                input: f(input)?,
+                redirect_stdout,
+                redirect_stderr,
+            },
         })
     }
 }
@@ -558,6 +589,7 @@ pub enum EngineCallResponse<D> {
     PipelineData(D),
     Config(SharedCow<Config>),
     ValueMap(HashMap<String, Value>),
+    Identifier(usize),
 }
 
 impl<D> EngineCallResponse<D> {
@@ -572,6 +604,7 @@ impl<D> EngineCallResponse<D> {
             EngineCallResponse::PipelineData(data) => EngineCallResponse::PipelineData(f(data)?),
             EngineCallResponse::Config(config) => EngineCallResponse::Config(config),
             EngineCallResponse::ValueMap(map) => EngineCallResponse::ValueMap(map),
+            EngineCallResponse::Identifier(id) => EngineCallResponse::Identifier(id),
         })
     }
 }

crates/nu-plugin/src/plugin/interface/mod.rs

@@ -6,14 +6,14 @@ use nu_plugin_core::{
     StreamManagerHandle,
 };
 use nu_plugin_protocol::{
-    CallInfo, CustomValueOp, EngineCall, EngineCallId, EngineCallResponse, Ordering, PluginCall,
+    CallInfo, CustomValueOp, EngineCall, EngineCallId, EngineCallResponse, EvaluatedCall, Ordering,
-    PluginCallId, PluginCallResponse, PluginCustomValue, PluginInput, PluginOption, PluginOutput,
+    PluginCall, PluginCallId, PluginCallResponse, PluginCustomValue, PluginInput, PluginOption,
-    ProtocolInfo,
+    PluginOutput, ProtocolInfo,
 };
 use nu_protocol::{
     engine::{ctrlc, Closure, Sequence},
-    Config, LabeledError, PipelineData, PluginMetadata, PluginSignature, ShellError, Signals, Span,
+    Config, DeclId, LabeledError, PipelineData, PluginMetadata, PluginSignature, ShellError,
-    Spanned, Value,
+    Signals, Span, Spanned, Value,
 };
 use nu_utils::SharedCow;
 use std::{
@@ -889,6 +889,71 @@ impl EngineInterface {
         }
     }
 
+    /// Ask the engine for the identifier for a declaration. If found, the result can then be passed
+    /// to [`.call_decl()`] to call other internal commands.
+    ///
+    /// See [`.call_decl()`] for an example.
+    pub fn find_decl(&self, name: impl Into<String>) -> Result<Option<DeclId>, ShellError> {
+        let call = EngineCall::FindDecl(name.into());
+
+        match self.engine_call(call)? {
+            EngineCallResponse::Error(err) => Err(err),
+            EngineCallResponse::Identifier(id) => Ok(Some(id)),
+            EngineCallResponse::PipelineData(PipelineData::Empty) => Ok(None),
+            _ => Err(ShellError::PluginFailedToDecode {
+                msg: "Received unexpected response type for EngineCall::FindDecl".into(),
+            }),
+        }
+    }
+
+    /// Ask the engine to call an internal command, using the declaration ID previously looked up
+    /// with [`.find_decl()`].
+    ///
+    /// # Example
+    ///
+    /// ```rust,no_run
+    /// # use nu_protocol::{Value, ShellError, PipelineData};
+    /// # use nu_plugin::{EngineInterface, EvaluatedCall};
+    /// # fn example(engine: &EngineInterface, call: &EvaluatedCall) -> Result<Value, ShellError> {
+    /// if let Some(decl_id) = engine.find_decl("scope commands")? {
+    ///     let commands = engine.call_decl(
+    ///         decl_id,
+    ///         EvaluatedCall::new(call.head),
+    ///         PipelineData::Empty,
+    ///         true,
+    ///         false,
+    ///     )?;
+    ///     commands.into_value(call.head)
+    /// } else {
+    ///     Ok(Value::list(vec![], call.head))
+    /// }
+    /// # }
+    /// ```
+    pub fn call_decl(
+        &self,
+        decl_id: DeclId,
+        call: EvaluatedCall,
+        input: PipelineData,
+        redirect_stdout: bool,
+        redirect_stderr: bool,
+    ) -> Result<PipelineData, ShellError> {
+        let call = EngineCall::CallDecl {
+            decl_id,
+            call,
+            input,
+            redirect_stdout,
+            redirect_stderr,
+        };
+
+        match self.engine_call(call)? {
+            EngineCallResponse::Error(err) => Err(err),
+            EngineCallResponse::PipelineData(data) => Ok(data),
+            _ => Err(ShellError::PluginFailedToDecode {
+                msg: "Received unexpected response type for EngineCall::CallDecl".into(),
+            }),
+        }
+    }
+
     /// Tell the engine whether to disable garbage collection for this plugin.
     ///
     /// The garbage collector is enabled by default, but plugins can turn it off (ideally

crates/nu-protocol/Cargo.toml

@@ -23,6 +23,7 @@ byte-unit = { version = "5.1", features = [ "serde" ] }
 chrono = { workspace = true, features = [ "serde", "std", "unstable-locales" ], default-features = false }
 chrono-humanize = { workspace = true }
 convert_case = { workspace = true }
+dirs = { workspace = true }
 fancy-regex = { workspace = true }
 indexmap = { workspace = true }
 lru = { workspace = true }
@@ -38,6 +39,10 @@ log = { workspace = true }
 [target.'cfg(unix)'.dependencies]
 nix = { workspace = true, default-features = false, features = ["signal"] }
 
+[target.'cfg(windows)'.dependencies]
+dirs-sys = { workspace = true }
+windows-sys = { workspace = true }
+
 [features]
 plugin = [
   "brotli",

crates/nu-protocol/src/ast/block.rs

@@ -78,6 +78,19 @@ impl Block {
             Type::Nothing
         }
     }
+
+    /// Replace any `$in` variables in the initial element of pipelines within the block
+    pub fn replace_in_variable(
+        &mut self,
+        working_set: &mut StateWorkingSet<'_>,
+        new_var_id: VarId,
+    ) {
+        for pipeline in self.pipelines.iter_mut() {
+            if let Some(element) = pipeline.elements.first_mut() {
+                element.replace_in_variable(working_set, new_var_id);
+            }
+        }
+    }
 }
 
 impl<T> From<T> for Block

crates/nu-protocol/src/ast/call.rs

@@ -110,17 +110,11 @@ impl Call {
     /// If there are one or more arguments the span encompasses the start of the first argument to
     /// end of the last argument
     pub fn arguments_span(&self) -> Span {
-        let past = self.head.past();
+        if self.arguments.is_empty() {
-
+            self.head.past()
-        let start = self
+        } else {
-            .arguments
+            Span::merge_many(self.arguments.iter().map(|a| a.span()))
-            .first()
+        }
-            .map(|a| a.span())
-            .unwrap_or(past)
-            .start;
-        let end = self.arguments.last().map(|a| a.span()).unwrap_or(past).end;
-
-        Span::new(start, end)
     }
 
     pub fn named_iter(
@@ -341,27 +335,7 @@ impl Call {
     }
 
     pub fn span(&self) -> Span {
-        let mut span = self.head;
+        self.head.merge(self.arguments_span())
-
-        for positional in self.positional_iter() {
-            if positional.span.end > span.end {
-                span.end = positional.span.end;
-            }
-        }
-
-        for (named, _, val) in self.named_iter() {
-            if named.span.end > span.end {
-                span.end = named.span.end;
-            }
-
-            if let Some(val) = &val {
-                if val.span.end > span.end {
-                    span.end = val.span.end;
-                }
-            }
-        }
-
-        span
     }
 }
 

crates/nu-protocol/src/ast/expr.rs

@@ -25,6 +25,7 @@ pub enum Expr {
     RowCondition(BlockId),
     UnaryNot(Box<Expression>),
     BinaryOp(Box<Expression>, Box<Expression>, Box<Expression>), //lhs, op, rhs
+    Collect(VarId, Box<Expression>),
     Subexpression(BlockId),
     Block(BlockId),
     Closure(BlockId),
@@ -65,11 +66,13 @@ impl Expr {
         &self,
         working_set: &StateWorkingSet,
     ) -> (Option<OutDest>, Option<OutDest>) {
-        // Usages of `$in` will be wrapped by a `collect` call by the parser,
-        // so we do not have to worry about that when considering
-        // which of the expressions below may consume pipeline output.
         match self {
             Expr::Call(call) => working_set.get_decl(call.decl_id).pipe_redirection(),
+            Expr::Collect(_, _) => {
+                // A collect expression always has default redirection, it's just going to collect
+                // stdout unless another type of redirection is specified
+                (None, None)
+            },
             Expr::Subexpression(block_id) | Expr::Block(block_id) => working_set
                 .get_block(*block_id)
                 .pipe_redirection(working_set),

crates/nu-protocol/src/ast/expression.rs

@@ -6,6 +6,8 @@ use crate::{
 use serde::{Deserialize, Serialize};
 use std::sync::Arc;
 
+use super::ListItem;
+
 /// Wrapper around [`Expr`]
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 pub struct Expression {
@@ -106,37 +108,14 @@ impl Expression {
                 left.has_in_variable(working_set) || right.has_in_variable(working_set)
             }
             Expr::UnaryNot(expr) => expr.has_in_variable(working_set),
-            Expr::Block(block_id) => {
+            Expr::Block(block_id) | Expr::Closure(block_id) => {
                 let block = working_set.get_block(*block_id);
-
+                block.captures.contains(&IN_VARIABLE_ID)
-                if block.captures.contains(&IN_VARIABLE_ID) {
+                    || block
-                    return true;
+                        .pipelines
-                }
+                        .iter()
-
+                        .flat_map(|pipeline| pipeline.elements.first())
-                if let Some(pipeline) = block.pipelines.first() {
+                        .any(|element| element.has_in_variable(working_set))
-                    match pipeline.elements.first() {
-                        Some(element) => element.has_in_variable(working_set),
-                        None => false,
-                    }
-                } else {
-                    false
-                }
-            }
-            Expr::Closure(block_id) => {
-                let block = working_set.get_block(*block_id);
-
-                if block.captures.contains(&IN_VARIABLE_ID) {
-                    return true;
-                }
-
-                if let Some(pipeline) = block.pipelines.first() {
-                    match pipeline.elements.first() {
-                        Some(element) => element.has_in_variable(working_set),
-                        None => false,
-                    }
-                } else {
-                    false
-                }
             }
             Expr::Binary(_) => false,
             Expr::Bool(_) => false,
@@ -251,6 +230,9 @@ impl Expression {
             Expr::Signature(_) => false,
             Expr::String(_) => false,
             Expr::RawString(_) => false,
+            // A `$in` variable found within a `Collect` is local, as it's already been wrapped
+            // This is probably unlikely to happen anyway - the expressions are wrapped depth-first
+            Expr::Collect(_, _) => false,
             Expr::RowCondition(block_id) | Expr::Subexpression(block_id) => {
                 let block = working_set.get_block(*block_id);
 
@@ -414,6 +396,7 @@ impl Expression {
                     i.replace_span(working_set, replaced, new_span)
                 }
             }
+            Expr::Collect(_, expr) => expr.replace_span(working_set, replaced, new_span),
             Expr::RowCondition(block_id) | Expr::Subexpression(block_id) => {
                 let mut block = (**working_set.get_block(*block_id)).clone();
 
@@ -443,6 +426,129 @@ impl Expression {
         }
     }
 
+    pub fn replace_in_variable(&mut self, working_set: &mut StateWorkingSet, new_var_id: VarId) {
+        match &mut self.expr {
+            Expr::Bool(_) => {}
+            Expr::Int(_) => {}
+            Expr::Float(_) => {}
+            Expr::Binary(_) => {}
+            Expr::Range(_) => {}
+            Expr::Var(var_id) | Expr::VarDecl(var_id) => {
+                if *var_id == IN_VARIABLE_ID {
+                    *var_id = new_var_id;
+                }
+            }
+            Expr::Call(call) => {
+                for arg in call.arguments.iter_mut() {
+                    match arg {
+                        Argument::Positional(expr)
+                        | Argument::Unknown(expr)
+                        | Argument::Named((_, _, Some(expr)))
+                        | Argument::Spread(expr) => {
+                            expr.replace_in_variable(working_set, new_var_id)
+                        }
+                        Argument::Named((_, _, None)) => {}
+                    }
+                }
+                for expr in call.parser_info.values_mut() {
+                    expr.replace_in_variable(working_set, new_var_id)
+                }
+            }
+            Expr::ExternalCall(head, args) => {
+                head.replace_in_variable(working_set, new_var_id);
+                for arg in args.iter_mut() {
+                    match arg {
+                        ExternalArgument::Regular(expr) | ExternalArgument::Spread(expr) => {
+                            expr.replace_in_variable(working_set, new_var_id)
+                        }
+                    }
+                }
+            }
+            Expr::Operator(_) => {}
+            // `$in` in `Collect` has already been handled, so we don't need to check further
+            Expr::Collect(_, _) => {}
+            Expr::Block(block_id)
+            | Expr::Closure(block_id)
+            | Expr::RowCondition(block_id)
+            | Expr::Subexpression(block_id) => {
+                let mut block = Block::clone(working_set.get_block(*block_id));
+                block.replace_in_variable(working_set, new_var_id);
+                *working_set.get_block_mut(*block_id) = block;
+            }
+            Expr::UnaryNot(expr) => {
+                expr.replace_in_variable(working_set, new_var_id);
+            }
+            Expr::BinaryOp(lhs, op, rhs) => {
+                for expr in [lhs, op, rhs] {
+                    expr.replace_in_variable(working_set, new_var_id);
+                }
+            }
+            Expr::MatchBlock(match_patterns) => {
+                for (_, expr) in match_patterns.iter_mut() {
+                    expr.replace_in_variable(working_set, new_var_id);
+                }
+            }
+            Expr::List(items) => {
+                for item in items.iter_mut() {
+                    match item {
+                        ListItem::Item(expr) | ListItem::Spread(_, expr) => {
+                            expr.replace_in_variable(working_set, new_var_id)
+                        }
+                    }
+                }
+            }
+            Expr::Table(table) => {
+                for col_expr in table.columns.iter_mut() {
+                    col_expr.replace_in_variable(working_set, new_var_id);
+                }
+                for row in table.rows.iter_mut() {
+                    for row_expr in row.iter_mut() {
+                        row_expr.replace_in_variable(working_set, new_var_id);
+                    }
+                }
+            }
+            Expr::Record(items) => {
+                for item in items.iter_mut() {
+                    match item {
+                        RecordItem::Pair(key, val) => {
+                            key.replace_in_variable(working_set, new_var_id);
+                            val.replace_in_variable(working_set, new_var_id);
+                        }
+                        RecordItem::Spread(_, expr) => {
+                            expr.replace_in_variable(working_set, new_var_id)
+                        }
+                    }
+                }
+            }
+            Expr::Keyword(kw) => kw.expr.replace_in_variable(working_set, new_var_id),
+            Expr::ValueWithUnit(value_with_unit) => value_with_unit
+                .expr
+                .replace_in_variable(working_set, new_var_id),
+            Expr::DateTime(_) => {}
+            Expr::Filepath(_, _) => {}
+            Expr::Directory(_, _) => {}
+            Expr::GlobPattern(_, _) => {}
+            Expr::String(_) => {}
+            Expr::RawString(_) => {}
+            Expr::CellPath(_) => {}
+            Expr::FullCellPath(full_cell_path) => {
+                full_cell_path
+                    .head
+                    .replace_in_variable(working_set, new_var_id);
+            }
+            Expr::ImportPattern(_) => {}
+            Expr::Overlay(_) => {}
+            Expr::Signature(_) => {}
+            Expr::StringInterpolation(exprs) | Expr::GlobInterpolation(exprs, _) => {
+                for expr in exprs.iter_mut() {
+                    expr.replace_in_variable(working_set, new_var_id);
+                }
+            }
+            Expr::Nothing => {}
+            Expr::Garbage => {}
+        }
+    }
+
     pub fn new(working_set: &mut StateWorkingSet, expr: Expr, span: Span, ty: Type) -> Expression {
         let span_id = working_set.add_span(span);
         Expression {

crates/nu-protocol/src/ast/pipeline.rs

@@ -1,4 +1,4 @@
-use crate::{ast::Expression, engine::StateWorkingSet, OutDest, Span};
+use crate::{ast::Expression, engine::StateWorkingSet, OutDest, Span, VarId};
 use serde::{Deserialize, Serialize};
 use std::fmt::Display;
 
@@ -62,6 +62,19 @@ impl RedirectionTarget {
             RedirectionTarget::Pipe { .. } => {}
         }
     }
+
+    pub fn replace_in_variable(
+        &mut self,
+        working_set: &mut StateWorkingSet<'_>,
+        new_var_id: VarId,
+    ) {
+        match self {
+            RedirectionTarget::File { expr, .. } => {
+                expr.replace_in_variable(working_set, new_var_id)
+            }
+            RedirectionTarget::Pipe { .. } => {}
+        }
+    }
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
@@ -75,6 +88,23 @@ pub enum PipelineRedirection {
         err: RedirectionTarget,
     },
 }
+impl PipelineRedirection {
+    pub fn replace_in_variable(
+        &mut self,
+        working_set: &mut StateWorkingSet<'_>,
+        new_var_id: VarId,
+    ) {
+        match self {
+            PipelineRedirection::Single { source: _, target } => {
+                target.replace_in_variable(working_set, new_var_id)
+            }
+            PipelineRedirection::Separate { out, err } => {
+                out.replace_in_variable(working_set, new_var_id);
+                err.replace_in_variable(working_set, new_var_id);
+            }
+        }
+    }
+}
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct PipelineElement {
@@ -120,6 +150,17 @@ impl PipelineElement {
     ) -> (Option<OutDest>, Option<OutDest>) {
         self.expr.expr.pipe_redirection(working_set)
     }
+
+    pub fn replace_in_variable(
+        &mut self,
+        working_set: &mut StateWorkingSet<'_>,
+        new_var_id: VarId,
+    ) {
+        self.expr.replace_in_variable(working_set, new_var_id);
+        if let Some(redirection) = &mut self.redirection {
+            redirection.replace_in_variable(working_set, new_var_id);
+        }
+    }
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]

crates/nu-protocol/src/debugger/profiler.rs

@@ -343,6 +343,7 @@ fn expr_to_string(engine_state: &EngineState, expr: &Expr) -> String {
         Expr::String(_) | Expr::RawString(_) => "string".to_string(),
         Expr::StringInterpolation(_) => "string interpolation".to_string(),
         Expr::GlobInterpolation(_, _) => "glob interpolation".to_string(),
+        Expr::Collect(_, _) => "collect".to_string(),
         Expr::Subexpression(_) => "subexpression".to_string(),
         Expr::Table(_) => "table".to_string(),
         Expr::UnaryNot(_) => "unary not".to_string(),

crates/nu-protocol/src/eval_base.rs

@@ -159,6 +159,9 @@ pub trait Eval {
             Expr::ExternalCall(head, args) => {
                 Self::eval_external_call(state, mut_state, head, args, expr_span)
             }
+            Expr::Collect(var_id, expr) => {
+                Self::eval_collect::<D>(state, mut_state, *var_id, expr)
+            }
             Expr::Subexpression(block_id) => {
                 Self::eval_subexpression::<D>(state, mut_state, *block_id, expr_span)
             }
@@ -356,6 +359,13 @@ pub trait Eval {
         span: Span,
     ) -> Result<Value, ShellError>;
 
+    fn eval_collect<D: DebugContext>(
+        state: Self::State<'_>,
+        mut_state: &mut Self::MutState,
+        var_id: VarId,
+        expr: &Expression,
+    ) -> Result<Value, ShellError>;
+
     fn eval_subexpression<D: DebugContext>(
         state: Self::State<'_>,
         mut_state: &mut Self::MutState,

crates/nu-protocol/src/eval_const.rs

@@ -185,24 +185,15 @@ pub(crate) fn create_nu_constant(engine_state: &EngineState, span: Span) -> Valu
         },
     );
 
-    // Create a system level directory for nushell scripts, modules, completions, etc
-    // that can be changed by setting the NU_VENDOR_AUTOLOAD_DIR env var on any platform
-    // before nushell is compiled OR if NU_VENDOR_AUTOLOAD_DIR is not set for non-windows
-    // systems, the PREFIX env var can be set before compile and used as PREFIX/nushell/vendor/autoload
     record.push(
-        "vendor-autoload-dir",
+        "vendor-autoload-dirs",
-        // pseudo code
+        Value::list(
-        // if env var NU_VENDOR_AUTOLOAD_DIR is set, in any platform, use it
+            get_vendor_autoload_dirs(engine_state)
-        // if not, if windows, use ALLUSERPROFILE\nushell\vendor\autoload
+                .iter()
-        // if not, if non-windows, if env var PREFIX is set, use PREFIX/share/nushell/vendor/autoload
+                .map(|path| Value::string(path.to_string_lossy(), span))
-        // if not, use the default /usr/share/nushell/vendor/autoload
+                .collect(),
-
+            span,
-        // check to see if NU_VENDOR_AUTOLOAD_DIR env var is set, if not, use the default
+        ),
-        if let Some(path) = get_vendor_autoload_dir(engine_state) {
-            Value::string(path.to_string_lossy(), span)
-        } else {
-            Value::error(ShellError::ConfigDirNotFound { span: Some(span) }, span)
-        },
     );
 
     record.push("temp-path", {
@@ -259,39 +250,95 @@ pub(crate) fn create_nu_constant(engine_state: &EngineState, span: Span) -> Valu
     Value::record(record, span)
 }
 
-pub fn get_vendor_autoload_dir(engine_state: &EngineState) -> Option<PathBuf> {
+pub fn get_vendor_autoload_dirs(_engine_state: &EngineState) -> Vec<PathBuf> {
-    // pseudo code
+    // load order for autoload dirs
-    // if env var NU_VENDOR_AUTOLOAD_DIR is set, in any platform, use it
+    // /Library/Application Support/nushell/vendor/autoload on macOS
-    // if not, if windows, use ALLUSERPROFILE\nushell\vendor\autoload
+    // <dir>/nushell/vendor/autoload for every dir in XDG_DATA_DIRS in reverse order on platforms other than windows. If XDG_DATA_DIRS is not set, it falls back to <PREFIX>/share if PREFIX ends in local, or <PREFIX>/local/share:<PREFIX>/share otherwise. If PREFIX is not set, fall back to /usr/local/share:/usr/share.
-    // if not, if non-windows, if env var PREFIX is set, use PREFIX/share/nushell/vendor/autoload
+    // %ProgramData%\nushell\vendor\autoload on windows
-    // if not, use the default /usr/share/nushell/vendor/autoload
+    // NU_VENDOR_AUTOLOAD_DIR from compile time, if env var is set at compile time
+    // if on macOS, additionally check XDG_DATA_HOME, which `dirs` is only doing on Linux
+    // <data_dir>/nushell/vendor/autoload of the current user according to the `dirs` crate
+    // NU_VENDOR_AUTOLOAD_DIR at runtime, if env var is set
 
-    // check to see if NU_VENDOR_AUTOLOAD_DIR env var is set, if not, use the default
+    let into_autoload_path_fn = |mut path: PathBuf| {
-    Some(
+        path.push("nushell");
-        option_env!("NU_VENDOR_AUTOLOAD_DIR")
+        path.push("vendor");
-            .map(String::from)
+        path.push("autoload");
-            .unwrap_or_else(|| {
+        path
-                if cfg!(windows) {
+    };
-                    let all_user_profile = match engine_state.get_env_var("ALLUSERPROFILE") {
+
-                        Some(v) => format!(
+    let mut dirs = Vec::new();
-                            "{}\\nushell\\vendor\\autoload",
+
-                            v.coerce_string().unwrap_or("C:\\ProgramData".into())
+    let mut append_fn = |path: PathBuf| {
-                        ),
+        if !dirs.contains(&path) {
-                        None => "C:\\ProgramData\\nushell\\vendor\\autoload".into(),
+            dirs.push(path)
-                    };
+        }
-                    all_user_profile
+    };
-                } else {
+
-                    // In non-Windows environments, if NU_VENDOR_AUTOLOAD_DIR is not set
+    #[cfg(target_os = "macos")]
-                    // check to see if PREFIX env var is set, and use it as PREFIX/nushell/vendor/autoload
+    std::iter::once("/Library/Application Support")
-                    // otherwise default to /usr/share/nushell/vendor/autoload
+        .map(PathBuf::from)
-                    option_env!("PREFIX").map(String::from).map_or_else(
+        .map(into_autoload_path_fn)
-                        || "/usr/local/share/nushell/vendor/autoload".into(),
+        .for_each(&mut append_fn);
-                        |prefix| format!("{}/share/nushell/vendor/autoload", prefix),
+    #[cfg(unix)]
-                    )
+    {
-                }
+        use std::os::unix::ffi::OsStrExt;
+
+        std::env::var_os("XDG_DATA_DIRS")
+            .or_else(|| {
+                option_env!("PREFIX").map(|prefix| {
+                    if prefix.ends_with("local") {
+                        std::ffi::OsString::from(format!("{prefix}/share"))
+                    } else {
+                        std::ffi::OsString::from(format!("{prefix}/local/share:{prefix}/share"))
+                    }
+                })
             })
-            .into(),
+            .unwrap_or_else(|| std::ffi::OsString::from("/usr/local/share/:/usr/share/"))
-    )
+            .as_encoded_bytes()
+            .split(|b| *b == b':')
+            .map(|split| into_autoload_path_fn(PathBuf::from(std::ffi::OsStr::from_bytes(split))))
+            .rev()
+            .for_each(&mut append_fn);
+    }
+
+    #[cfg(target_os = "windows")]
+    dirs_sys::known_folder(windows_sys::Win32::UI::Shell::FOLDERID_ProgramData)
+        .into_iter()
+        .map(into_autoload_path_fn)
+        .for_each(&mut append_fn);
+
+    option_env!("NU_VENDOR_AUTOLOAD_DIR")
+        .into_iter()
+        .map(PathBuf::from)
+        .for_each(&mut append_fn);
+
+    #[cfg(target_os = "macos")]
+    std::env::var("XDG_DATA_HOME")
+        .ok()
+        .map(PathBuf::from)
+        .or_else(|| {
+            dirs::home_dir().map(|mut home| {
+                home.push(".local");
+                home.push("share");
+                home
+            })
+        })
+        .map(into_autoload_path_fn)
+        .into_iter()
+        .for_each(&mut append_fn);
+
+    dirs::data_dir()
+        .into_iter()
+        .map(into_autoload_path_fn)
+        .for_each(&mut append_fn);
+
+    std::env::var_os("NU_VENDOR_AUTOLOAD_DIR")
+        .into_iter()
+        .map(PathBuf::from)
+        .for_each(&mut append_fn);
+
+    dirs
 }
 
 fn eval_const_call(
@@ -422,6 +469,15 @@ impl Eval for EvalConst {
         Err(ShellError::NotAConstant { span })
     }
 
+    fn eval_collect<D: DebugContext>(
+        _: &StateWorkingSet,
+        _: &mut (),
+        _var_id: VarId,
+        expr: &Expression,
+    ) -> Result<Value, ShellError> {
+        Err(ShellError::NotAConstant { span: expr.span })
+    }
+
     fn eval_subexpression<D: DebugContext>(
         working_set: &StateWorkingSet,
         _: &mut (),

crates/nu-protocol/src/ir/call.rs

@@ -239,7 +239,7 @@ impl CallBuilder {
         }
         self.inner.args_len += 1;
         if let Some(span) = argument.span() {
-            self.inner.span = self.inner.span.append(span);
+            self.inner.span = self.inner.span.merge(span);
         }
         stack.arguments.push(argument);
         self

crates/nu-protocol/src/ir/display.rs

@@ -102,6 +102,10 @@ impl<'a> fmt::Display for FmtInstruction<'a> {
                 let var = FmtVar::new(self.engine_state, *var_id);
                 write!(f, "{:WIDTH$} {var}, {src}", "store-variable")
             }
+            Instruction::DropVariable { var_id } => {
+                let var = FmtVar::new(self.engine_state, *var_id);
+                write!(f, "{:WIDTH$} {var}", "drop-variable")
+            }
             Instruction::LoadEnv { dst, key } => {
                 let key = FmtData(self.data, *key);
                 write!(f, "{:WIDTH$} {dst}, {key}", "load-env")

crates/nu-protocol/src/ir/mod.rs

@@ -127,6 +127,8 @@ pub enum Instruction {
     LoadVariable { dst: RegId, var_id: VarId },
     /// Store the value of a variable from the `src` register
     StoreVariable { var_id: VarId, src: RegId },
+    /// Remove a variable from the stack, freeing up whatever resources were associated with it
+    DropVariable { var_id: VarId },
     /// Load the value of an environment variable into the `dst` register
     LoadEnv { dst: RegId, key: DataSlice },
     /// Load the value of an environment variable into the `dst` register, or `Nothing` if it
@@ -290,6 +292,7 @@ impl Instruction {
             Instruction::Drain { .. } => None,
             Instruction::LoadVariable { dst, .. } => Some(dst),
             Instruction::StoreVariable { .. } => None,
+            Instruction::DropVariable { .. } => None,
             Instruction::LoadEnv { dst, .. } => Some(dst),
             Instruction::LoadEnvOpt { dst, .. } => Some(dst),
             Instruction::StoreEnv { .. } => None,

crates/nu-protocol/src/syntax_shape.rs

@@ -47,6 +47,12 @@ pub enum SyntaxShape {
     /// A general expression, eg `1 + 2` or `foo --bar`
     Expression,
 
+    /// A (typically) string argument that follows external command argument parsing rules.
+    ///
+    /// Filepaths are expanded if unquoted, globs are allowed, and quotes embedded within unknown
+    /// args are unquoted.
+    ExternalArgument,
+
     /// A filepath is allowed
     Filepath,
 
@@ -145,6 +151,7 @@ impl SyntaxShape {
             SyntaxShape::DateTime => Type::Date,
             SyntaxShape::Duration => Type::Duration,
             SyntaxShape::Expression => Type::Any,
+            SyntaxShape::ExternalArgument => Type::Any,
             SyntaxShape::Filepath => Type::String,
             SyntaxShape::Directory => Type::String,
             SyntaxShape::Float => Type::Float,
@@ -238,6 +245,7 @@ impl Display for SyntaxShape {
             SyntaxShape::Signature => write!(f, "signature"),
             SyntaxShape::MatchBlock => write!(f, "match-block"),
             SyntaxShape::Expression => write!(f, "expression"),
+            SyntaxShape::ExternalArgument => write!(f, "external-argument"),
             SyntaxShape::Boolean => write!(f, "bool"),
             SyntaxShape::Error => write!(f, "error"),
             SyntaxShape::CompleterWrapper(x, _) => write!(f, "completable<{x}>"),

crates/nu-utils/src/sample_config/default_config.nu

@@ -47,7 +47,7 @@ let dark_theme = {
     shape_flag: blue_bold
     shape_float: purple_bold
     # shapes are used to change the cli syntax highlighting
-    shape_garbage: { fg: white bg: red attr: b}
+    shape_garbage: { fg: white bg: red attr: b }
     shape_glob_interpolation: cyan_bold
     shape_globpattern: cyan_bold
     shape_int: purple_bold
@@ -114,7 +114,8 @@ let light_theme = {
     shape_flag: blue_bold
     shape_float: purple_bold
     # shapes are used to change the cli syntax highlighting
-    shape_garbage: { fg: white bg: red attr: b}
+    shape_garbage: { fg: white bg: red attr: b }
+    shape_glob_interpolation: cyan_bold
     shape_globpattern: cyan_bold
     shape_int: purple_bold
     shape_internalcall: cyan_bold
@@ -226,9 +227,9 @@ $env.config = {
 
     color_config: $dark_theme # if you want a more interesting theme, you can replace the empty record with `$dark_theme`, `$light_theme` or another custom record
     use_grid_icons: true
-    footer_mode: "25" # always, never, number_of_rows, auto
+    footer_mode: 25 # always, never, number_of_rows, auto
     float_precision: 2 # the precision for displaying floats in tables
-    buffer_editor: "" # command that will be used to edit the current line buffer with ctrl+o, if unset fallback to $env.EDITOR and $env.VISUAL
+    buffer_editor: null # command that will be used to edit the current line buffer with ctrl+o, if unset fallback to $env.EDITOR and $env.VISUAL
     use_ansi_coloring: true
     bracketed_paste: true # enable bracketed paste, currently useless on windows
     edit_mode: emacs # emacs, vi
@@ -888,4 +889,4 @@ $env.config = {
             event: { edit: selectall }
         }
     ]
-}
+}

crates/nu_plugin_example/src/commands/call_decl.rs

@@ -0,0 +1,78 @@
+use nu_plugin::{EngineInterface, EvaluatedCall, PluginCommand};
+use nu_protocol::{
+    IntoSpanned, LabeledError, PipelineData, Record, Signature, Spanned, SyntaxShape, Value,
+};
+
+use crate::ExamplePlugin;
+
+pub struct CallDecl;
+
+impl PluginCommand for CallDecl {
+    type Plugin = ExamplePlugin;
+
+    fn name(&self) -> &str {
+        "example call-decl"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build(self.name())
+            .required(
+                "name",
+                SyntaxShape::String,
+                "the name of the command to call",
+            )
+            .optional(
+                "named_args",
+                SyntaxShape::Record(vec![]),
+                "named arguments to pass to the command",
+            )
+            .rest(
+                "positional_args",
+                SyntaxShape::Any,
+                "positional arguments to pass to the command",
+            )
+    }
+
+    fn usage(&self) -> &str {
+        "Demonstrates calling other commands from plugins using `call_decl()`."
+    }
+
+    fn extra_usage(&self) -> &str {
+        "
+The arguments will not be typechecked at parse time. This command is for
+demonstration only, and should not be used for anything real.
+"
+        .trim()
+    }
+
+    fn run(
+        &self,
+        _plugin: &ExamplePlugin,
+        engine: &EngineInterface,
+        call: &EvaluatedCall,
+        input: PipelineData,
+    ) -> Result<PipelineData, LabeledError> {
+        let name: Spanned<String> = call.req(0)?;
+        let named_args: Option<Record> = call.opt(1)?;
+        let positional_args: Vec<Value> = call.rest(2)?;
+
+        let decl_id = engine.find_decl(&name.item)?.ok_or_else(|| {
+            LabeledError::new(format!("Can't find `{}`", name.item))
+                .with_label("not in scope", name.span)
+        })?;
+
+        let mut new_call = EvaluatedCall::new(call.head);
+
+        for (key, val) in named_args.into_iter().flatten() {
+            new_call.add_named(key.into_spanned(val.span()), val);
+        }
+
+        for val in positional_args {
+            new_call.add_positional(val);
+        }
+
+        let result = engine.call_decl(decl_id, new_call, input, true, false)?;
+
+        Ok(result)
+    }
+}

crates/nu_plugin_example/src/commands/mod.rs

@@ -13,12 +13,14 @@ pub use three::Three;
 pub use two::Two;
 
 // Engine interface demos
+mod call_decl;
 mod config;
 mod ctrlc;
 mod disable_gc;
 mod env;
 mod view_span;
 
+pub use call_decl::CallDecl;
 pub use config::Config;
 pub use ctrlc::Ctrlc;
 pub use disable_gc::DisableGc;

crates/nu_plugin_example/src/lib.rs

@@ -28,6 +28,7 @@ impl Plugin for ExamplePlugin {
             Box::new(ViewSpan),
             Box::new(DisableGc),
             Box::new(Ctrlc),
+            Box::new(CallDecl),
             // Stream demos
             Box::new(CollectBytes),
             Box::new(Echo),

crates/nu_plugin_query/src/query_web.rs

@@ -76,7 +76,7 @@ pub fn web_examples() -> Vec<Example<'static>> {
         },
         Example {
             example: "http get https://en.wikipedia.org/wiki/List_of_cities_in_India_by_population |
-        query web --as-table [City 'Population(2011)[3]' 'Population(2001)[3][a]' 'State or unionterritory' 'Ref']",
+        query web --as-table [City 'Population(2011)[3]' 'Population(2001)[3][a]' 'State or unionterritory' 'Reference']",
             description: "Retrieve a html table from Wikipedia and parse it into a nushell table using table headers as guides",
             result: None
         },

crates/nuon/src/from.rs

@@ -329,6 +329,12 @@ fn convert_to_value(
             msg: "glob interpolation not supported in nuon".into(),
             span: expr.span,
         }),
+        Expr::Collect(..) => Err(ShellError::OutsideSpannedLabeledError {
+            src: original_text.to_string(),
+            error: "Error when loading".into(),
+            msg: "`$in` not supported in nuon".into(),
+            span: expr.span,
+        }),
         Expr::Subexpression(..) => Err(ShellError::OutsideSpannedLabeledError {
             src: original_text.to_string(),
             error: "Error when loading".into(),

src/config_files.rs

@@ -200,8 +200,7 @@ pub(crate) fn read_vendor_autoload_files(engine_state: &mut EngineState, stack:
         column!()
     );
 
-    // read and source vendor_autoload_files file if exists
+    for autoload_dir in nu_protocol::eval_const::get_vendor_autoload_dirs(engine_state) {
-    if let Some(autoload_dir) = nu_protocol::eval_const::get_vendor_autoload_dir(engine_state) {
         warn!("read_vendor_autoload_files: {}", autoload_dir.display());
 
         if autoload_dir.exists() {

tests/plugins/call_decl.rs

@@ -0,0 +1,42 @@
+use nu_test_support::nu_with_plugins;
+
+#[test]
+fn call_to_json() {
+    let result = nu_with_plugins!(
+        cwd: ".",
+        plugin: ("nu_plugin_example"),
+        r#"
+            [42] | example call-decl 'to json' {indent: 4}
+        "#
+    );
+    assert!(result.status.success());
+    // newlines are removed from test output
+    assert_eq!("[    42]", result.out);
+}
+
+#[test]
+fn call_reduce() {
+    let result = nu_with_plugins!(
+        cwd: ".",
+        plugin: ("nu_plugin_example"),
+        r#"
+            [1 2 3] | example call-decl 'reduce' {fold: 10} { |it, acc| $it + $acc }
+        "#
+    );
+    assert!(result.status.success());
+    assert_eq!("16", result.out);
+}
+
+#[test]
+fn call_scope_variables() {
+    let result = nu_with_plugins!(
+        cwd: ".",
+        plugin: ("nu_plugin_example"),
+        r#"
+            let test_var = 10
+            example call-decl 'scope variables' | where name == '$test_var' | length
+        "#
+    );
+    assert!(result.status.success());
+    assert_eq!("1", result.out);
+}

tests/plugins/mod.rs

@@ -1,3 +1,4 @@
+mod call_decl;
 mod config;
 mod core_inc;
 mod custom_values;

tests/repl/test_custom_commands.rs

@@ -186,8 +186,12 @@ fn help_present_in_def() -> TestResult {
 #[test]
 fn help_not_present_in_extern() -> TestResult {
     run_test(
-        "module test {export extern \"git fetch\" []}; use test `git fetch`; help git fetch | ansi strip",
+        r#"
-        "Usage:\n  > git fetch",
+            module test {export extern "git fetch" []};
+            use test `git fetch`;
+            help git fetch | find help | to text | ansi strip
+        "#,
+        "",
     )
 }
 

tests/repl/test_engine.rs

@@ -52,6 +52,29 @@ fn in_and_if_else() -> TestResult {
     )
 }
 
+#[test]
+fn in_with_closure() -> TestResult {
+    // Can use $in twice
+    run_test(r#"3 | do { let x = $in; let y = $in; $x + $y }"#, "6")
+}
+
+#[test]
+fn in_with_custom_command() -> TestResult {
+    // Can use $in twice
+    run_test(
+        r#"def foo [] { let x = $in; let y = $in; $x + $y }; 3 | foo"#,
+        "6",
+    )
+}
+
+#[test]
+fn in_used_twice_and_also_in_pipeline() -> TestResult {
+    run_test(
+        r#"3 | do { let x = $in; let y = $in; $x + $y | $in * 4 }"#,
+        "24",
+    )
+}
+
 #[test]
 fn help_works_with_missing_requirements() -> TestResult {
     run_test(r#"each --help | lines | length"#, "72")

tests/repl/test_known_external.rs

@@ -137,3 +137,39 @@ fn known_external_aliased_subcommand_from_module() -> TestResult {
         String::from_utf8(output.stdout)?.trim(),
     )
 }
+
+#[test]
+fn known_external_arg_expansion() -> TestResult {
+    run_test(
+        r#"
+            extern echo [];
+            echo ~/foo
+        "#,
+        &dirs::home_dir()
+            .expect("can't find home dir")
+            .join("foo")
+            .to_string_lossy(),
+    )
+}
+
+#[test]
+fn known_external_arg_quoted_no_expand() -> TestResult {
+    run_test(
+        r#"
+            extern echo [];
+            echo "~/foo"
+        "#,
+        "~/foo",
+    )
+}
+
+#[test]
+fn known_external_arg_internally_quoted_options() -> TestResult {
+    run_test(
+        r#"
+            extern echo [];
+            echo --option="test"
+        "#,
+        "--option=test",
+    )
+}

tests/repl/test_type_check.rs

@@ -129,3 +129,16 @@ fn transpose_into_load_env() -> TestResult {
         "10",
     )
 }
+
+#[test]
+fn in_variable_expression_correct_output_type() -> TestResult {
+    run_test(r#"def foo []: nothing -> string { 'foo' | $"($in)" }"#, "")
+}
+
+#[test]
+fn in_variable_expression_wrong_output_type() -> TestResult {
+    fail_test(
+        r#"def foo []: nothing -> int { 'foo' | $"($in)" }"#,
+        "expected int",
+    )
+}