Debugger experiments (#11441)

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# Description
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This PR adds a new evaluator path with callbacks to a mutable trait
object implementing a Debugger trait. The trait object can do anything,
e.g., profiling, code coverage, step debugging. Currently,
entering/leaving a block and a pipeline element is marked with
callbacks, but more callbacks can be added as necessary. Not all
callbacks need to be used by all debuggers; unused ones are simply empty
calls. A simple profiler is implemented as a proof of concept.

The debugging support is implementing by making `eval_xxx()` functions
generic depending on whether we're debugging or not. This has zero
computational overhead, but makes the binary slightly larger (see
benchmarks below). `eval_xxx()` variants called from commands (like
`eval_block_with_early_return()` in `each`) are chosen with a dynamic
dispatch for two reasons: to not grow the binary size due to duplicating
the code of many commands, and for the fact that it isn't possible
because it would make Command trait objects object-unsafe.

In the future, I hope it will be possible to allow plugin callbacks such
that users would be able to implement their profiler plugins instead of
having to recompile Nushell.
[DAP](https://microsoft.github.io/debug-adapter-protocol/) would also be
interesting to explore.

Try `help debug profile`.

## Screenshots

Basic output:

![profiler_new](https://github.com/nushell/nushell/assets/25571562/418b9df0-b659-4dcb-b023-2d5fcef2c865)

To profile with more granularity, increase the profiler depth (you'll
see that repeated `is-windows` calls take a large chunk of total time,
making it a good candidate for optimizing):

![profiler_new_m3](https://github.com/nushell/nushell/assets/25571562/636d756d-5d56-460c-a372-14716f65f37f)

## Benchmarks

### Binary size

Binary size increase vs. main: **+40360 bytes**. _(Both built with
`--release --features=extra,dataframe`.)_

### Time

```nushell
# bench_debug.nu
use std bench

let test = {
    1..100
    | each {
        ls | each {|row| $row.name | str length }
    }
    | flatten
    | math avg
}

print 'debug:'
let res2 = bench { debug profile $test } --pretty
print $res2
```

```nushell
# bench_nodebug.nu
use std bench

let test = {
    1..100
    | each {
        ls | each {|row| $row.name | str length }
    }
    | flatten
    | math avg
}

print 'no debug:'
let res1 = bench { do $test } --pretty
print $res1
```

`cargo run --release -- bench_debug.nu` is consistently 1--2 ms slower
than `cargo run --release -- bench_nodebug.nu` due to the collection
overhead + gathering the report. This is expected. When gathering more
stuff, the overhead is obviously higher.

`cargo run --release -- bench_nodebug.nu` vs. `nu bench_nodebug.nu` I
didn't measure any difference. Both benchmarks report times between 97
and 103 ms randomly, without one being consistently higher than the
other. This suggests that at least in this particular case, when not
running any debugger, there is no runtime overhead.

## API changes

This PR adds a generic parameter to all `eval_xxx` functions that forces
you to specify whether you use the debugger. You can resolve it in two
ways:
* Use a provided helper that will figure it out for you. If you wanted
to use `eval_block(&engine_state, ...)`, call `let eval_block =
get_eval_block(&engine_state); eval_block(&engine_state, ...)`
* If you know you're in an evaluation path that doesn't need debugger
support, call `eval_block::<WithoutDebug>(&engine_state, ...)` (this is
the case of hooks, for example).

I tried to add more explanation in the docstring of `debugger_trait.rs`.

## TODO

- [x] Better profiler output to reduce spam of iterative commands like
`each`
- [x] Resolve `TODO: DEBUG` comments
- [x] Resolve unwraps
- [x] Add doc comments
- [x] Add usage and extra usage for `debug profile`, explaining all
columns

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

Hopefully none.

# Tests + Formatting
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crates/nu-cli/src/completions/completer.rs

@@ -5,6 +5,7 @@ use crate::completions::{
 use nu_color_config::{color_record_to_nustyle, lookup_ansi_color_style};
 use nu_engine::eval_block;
 use nu_parser::{flatten_expression, parse, FlatShape};
+use nu_protocol::debugger::WithoutDebug;
 use nu_protocol::{
     ast::PipelineElement,
     engine::{EngineState, Stack, StateWorkingSet},
@@ -83,7 +84,7 @@ impl NuCompleter {
             }
         }
 
-        let result = eval_block(
+        let result = eval_block::<WithoutDebug>(
             &self.engine_state,
             &mut callee_stack,
             block,

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

@@ -1,5 +1,6 @@
 use crate::completions::{Completer, CompletionOptions, MatchAlgorithm, SortBy};
 use nu_engine::eval_call;
+use nu_protocol::debugger::WithoutDebug;
 use nu_protocol::{
     ast::{Argument, Call, Expr, Expression},
     engine::{EngineState, Stack, StateWorkingSet},
@@ -46,7 +47,7 @@ impl Completer for CustomCompletion {
         let line_pos = pos - offset;
 
         // Call custom declaration
-        let result = eval_call(
+        let result = eval_call::<WithoutDebug>(
             &self.engine_state,
             &mut self.stack,
             &Call {

crates/nu-cli/src/eval_cmds.rs

@@ -2,6 +2,7 @@ use log::info;
 use miette::Result;
 use nu_engine::{convert_env_values, eval_block};
 use nu_parser::parse;
+use nu_protocol::debugger::WithoutDebug;
 use nu_protocol::engine::Stack;
 use nu_protocol::report_error;
 use nu_protocol::{
@@ -55,21 +56,27 @@ pub fn evaluate_commands(
     }
 
     // Run the block
-    let exit_code = match eval_block(engine_state, stack, &block, input, false, false) {
-        Ok(pipeline_data) => {
-            let mut config = engine_state.get_config().clone();
-            if let Some(t_mode) = table_mode {
-                config.table_mode = t_mode.coerce_str()?.parse().unwrap_or_default();
+    let exit_code =
+        match eval_block::<WithoutDebug>(engine_state, stack, &block, input, false, false) {
+            Ok(pipeline_data) => {
+                let mut config = engine_state.get_config().clone();
+                if let Some(t_mode) = table_mode {
+                    config.table_mode = t_mode.coerce_str()?.parse().unwrap_or_default();
+                }
+                crate::eval_file::print_table_or_error(
+                    engine_state,
+                    stack,
+                    pipeline_data,
+                    &mut config,
+                )
             }
-            crate::eval_file::print_table_or_error(engine_state, stack, pipeline_data, &mut config)
-        }
-        Err(err) => {
-            let working_set = StateWorkingSet::new(engine_state);
+            Err(err) => {
+                let working_set = StateWorkingSet::new(engine_state);
 
-            report_error(&working_set, &err);
-            std::process::exit(1);
-        }
-    };
+                report_error(&working_set, &err);
+                std::process::exit(1);
+            }
+        };
 
     info!("evaluate {}:{}:{}", file!(), line!(), column!());
 

crates/nu-cli/src/eval_file.rs

@@ -6,6 +6,7 @@ use nu_engine::eval_block;
 use nu_engine::{convert_env_values, current_dir};
 use nu_parser::parse;
 use nu_path::canonicalize_with;
+use nu_protocol::debugger::WithoutDebug;
 use nu_protocol::report_error;
 use nu_protocol::{
     ast::Call,
@@ -130,7 +131,7 @@ pub fn evaluate_file(
     if engine_state.find_decl(b"main", &[]).is_some() {
         let args = format!("main {}", args.join(" "));
 
-        let pipeline_data = eval_block(
+        let pipeline_data = eval_block::<WithoutDebug>(
             engine_state,
             stack,
             &block,

crates/nu-cli/src/menus/menu_completions.rs

@@ -1,4 +1,5 @@
 use nu_engine::eval_block;
+use nu_protocol::debugger::WithoutDebug;
 use nu_protocol::{
     engine::{EngineState, Stack},
     IntoPipelineData, Span, Value,
@@ -55,7 +56,8 @@ impl Completer for NuMenuCompleter {
         }
 
         let input = Value::nothing(self.span).into_pipeline_data();
-        let res = eval_block(
+
+        let res = eval_block::<WithoutDebug>(
             &self.engine_state,
             &mut self.stack,
             block,

crates/nu-cli/src/prompt_update.rs

@@ -1,6 +1,7 @@
 use crate::NushellPrompt;
 use log::trace;
-use nu_engine::eval_subexpression;
+use nu_engine::get_eval_subexpression;
+
 use nu_protocol::report_error;
 use nu_protocol::{
     engine::{EngineState, Stack, StateWorkingSet},
@@ -35,6 +36,8 @@ fn get_prompt_string(
     engine_state: &EngineState,
     stack: &mut Stack,
 ) -> Option<String> {
+    let eval_subexpression = get_eval_subexpression(engine_state);
+
     stack
         .get_env_var(engine_state, prompt)
         .and_then(|v| match v {

crates/nu-cli/src/reedline_config.rs

@@ -3,6 +3,7 @@ use crossterm::event::{KeyCode, KeyModifiers};
 use nu_color_config::{color_record_to_nustyle, lookup_ansi_color_style};
 use nu_engine::eval_block;
 use nu_parser::parse;
+use nu_protocol::debugger::WithoutDebug;
 use nu_protocol::{
     create_menus,
     engine::{EngineState, Stack, StateWorkingSet},
@@ -110,7 +111,15 @@ pub(crate) fn add_menus(
 
             let mut temp_stack = Stack::new();
             let input = PipelineData::Empty;
-            let res = eval_block(&engine_state, &mut temp_stack, &block, input, false, false)?;
+
+            let res = eval_block::<WithoutDebug>(
+                &engine_state,
+                &mut temp_stack,
+                &block,
+                input,
+                false,
+                false,
+            )?;
 
             if let PipelineData::Value(value, None) = res {
                 for menu in create_menus(&value)? {

crates/nu-cli/src/util.rs

@@ -1,6 +1,7 @@
 use nu_cmd_base::hook::eval_hook;
 use nu_engine::{eval_block, eval_block_with_early_return};
 use nu_parser::{escape_quote_string, lex, parse, unescape_unquote_string, Token, TokenContents};
+use nu_protocol::debugger::WithoutDebug;
 use nu_protocol::engine::StateWorkingSet;
 use nu_protocol::{
     engine::{EngineState, Stack},
@@ -240,9 +241,16 @@ pub fn eval_source(
     }
 
     let b = if allow_return {
-        eval_block_with_early_return(engine_state, stack, &block, input, false, false)
+        eval_block_with_early_return::<WithoutDebug>(
+            engine_state,
+            stack,
+            &block,
+            input,
+            false,
+            false,
+        )
     } else {
-        eval_block(engine_state, stack, &block, input, false, false)
+        eval_block::<WithoutDebug>(engine_state, stack, &block, input, false, false)
     };
 
     match b {

crates/nu-cli/tests/support/completions_helpers.rs

@@ -2,6 +2,7 @@ use std::path::PathBuf;
 
 use nu_engine::eval_block;
 use nu_parser::parse;
+use nu_protocol::debugger::WithoutDebug;
 use nu_protocol::{
     engine::{EngineState, Stack, StateWorkingSet},
     eval_const::create_nu_constant,
@@ -9,6 +10,7 @@ use nu_protocol::{
 };
 use nu_test_support::fs;
 use reedline::Suggestion;
+
 const SEP: char = std::path::MAIN_SEPARATOR;
 
 fn create_default_context() -> EngineState {
@@ -194,13 +196,13 @@ pub fn merge_input(
 
     engine_state.merge_delta(delta)?;
 
-    assert!(eval_block(
+    assert!(eval_block::<WithoutDebug>(
         engine_state,
         stack,
         &block,
         PipelineData::Value(Value::nothing(Span::unknown(),), None),
         false,
-        false
+        false,
     )
     .is_ok());
 

crates/nu-cmd-base/src/hook.rs

@@ -3,6 +3,7 @@ use miette::Result;
 use nu_engine::{eval_block, eval_block_with_early_return};
 use nu_parser::parse;
 use nu_protocol::cli_error::{report_error, report_error_new};
+use nu_protocol::debugger::WithoutDebug;
 use nu_protocol::engine::{EngineState, Stack, StateWorkingSet};
 use nu_protocol::{BlockId, PipelineData, PositionalArg, ShellError, Span, Type, Value, VarId};
 
@@ -115,7 +116,7 @@ pub fn eval_hook(
                 })
                 .collect();
 
-            match eval_block(engine_state, stack, &block, input, false, false) {
+            match eval_block::<WithoutDebug>(engine_state, stack, &block, input, false, false) {
                 Ok(pipeline_data) => {
                     output = pipeline_data;
                 }
@@ -243,7 +244,14 @@ pub fn eval_hook(
                             })
                             .collect();
 
-                        match eval_block(engine_state, stack, &block, input, false, false) {
+                        match eval_block::<WithoutDebug>(
+                            engine_state,
+                            stack,
+                            &block,
+                            input,
+                            false,
+                            false,
+                        ) {
                             Ok(pipeline_data) => {
                                 output = pipeline_data;
                             }
@@ -336,8 +344,14 @@ fn run_hook_block(
         }
     }
 
-    let pipeline_data =
-        eval_block_with_early_return(engine_state, &mut callee_stack, block, input, false, false)?;
+    let pipeline_data = eval_block_with_early_return::<WithoutDebug>(
+        engine_state,
+        &mut callee_stack,
+        block,
+        input,
+        false,
+        false,
+    )?;
 
     if let PipelineData::Value(Value::Error { error, .. }, _) = pipeline_data {
         return Err(*error);

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

@@ -10,6 +10,7 @@ use super::expressions::ExprCol;
 use super::lazy::LazyFillNull;
 use super::lazy::{LazyCollect, ToLazyFrame};
 use nu_cmd_lang::Let;
+use nu_protocol::debugger::WithoutDebug;
 
 pub fn test_dataframe(cmds: Vec<Box<dyn Command + 'static>>) {
     if cmds.is_empty() {
@@ -80,7 +81,7 @@ pub fn test_dataframe_example(engine_state: &mut Box<EngineState>, example: &Exa
 
     let mut stack = Stack::new();
 
-    let result = eval_block(
+    let result = eval_block::<WithoutDebug>(
         engine_state,
         &mut stack,
         &block,

crates/nu-cmd-extra/src/extra/filters/each_while.rs

@@ -1,5 +1,6 @@
-use nu_engine::{eval_block_with_early_return, CallExt};
+use nu_engine::{get_eval_block_with_early_return, CallExt};
 use nu_protocol::ast::Call;
+
 use nu_protocol::engine::{Closure, Command, EngineState, Stack};
 use nu_protocol::{
     Category, Example, IntoInterruptiblePipelineData, IntoPipelineData, PipelineData, ShellError,
@@ -84,6 +85,7 @@ impl Command for EachWhile {
         let span = call.head;
         let redirect_stdout = call.redirect_stdout;
         let redirect_stderr = call.redirect_stderr;
+        let eval_block_with_early_return = get_eval_block_with_early_return(&engine_state);
 
         match input {
             PipelineData::Empty => Ok(PipelineData::Empty),

crates/nu-cmd-extra/src/extra/filters/update_cells.rs

@@ -1,5 +1,6 @@
-use nu_engine::{eval_block, CallExt};
+use nu_engine::{get_eval_block, CallExt, EvalBlockFn};
 use nu_protocol::ast::{Block, Call};
+
 use nu_protocol::engine::{Closure, Command, EngineState, Stack};
 use nu_protocol::{
     record, Category, Example, IntoInterruptiblePipelineData, IntoPipelineData, PipelineData,
@@ -102,6 +103,7 @@ impl Command for UpdateCells {
         let metadata = input.metadata();
         let ctrlc = engine_state.ctrlc.clone();
         let block: Block = engine_state.get_block(block.block_id).clone();
+        let eval_block_fn = get_eval_block(&engine_state);
 
         let redirect_stdout = call.redirect_stdout;
         let redirect_stderr = call.redirect_stderr;
@@ -131,6 +133,7 @@ impl Command for UpdateCells {
             redirect_stdout,
             redirect_stderr,
             span,
+            eval_block_fn,
         }
         .into_pipeline_data(ctrlc)
         .set_metadata(metadata))
@@ -145,6 +148,7 @@ struct UpdateCellIterator {
     block: Block,
     redirect_stdout: bool,
     redirect_stderr: bool,
+    eval_block_fn: EvalBlockFn,
     span: Span,
 }
 
@@ -176,6 +180,7 @@ impl Iterator for UpdateCellIterator {
                                         self.redirect_stdout,
                                         self.redirect_stderr,
                                         span,
+                                        self.eval_block_fn,
                                     ),
                                 ),
                             })
@@ -190,6 +195,7 @@ impl Iterator for UpdateCellIterator {
                         self.redirect_stdout,
                         self.redirect_stderr,
                         self.span,
+                        self.eval_block_fn,
                     )),
                 }
             }
@@ -198,6 +204,7 @@ impl Iterator for UpdateCellIterator {
     }
 }
 
+#[allow(clippy::too_many_arguments)]
 fn process_cell(
     val: Value,
     engine_state: &EngineState,
@@ -206,13 +213,15 @@ fn process_cell(
     redirect_stdout: bool,
     redirect_stderr: bool,
     span: Span,
+    eval_block_fn: EvalBlockFn,
 ) -> Value {
     if let Some(var) = block.signature.get_positional(0) {
         if let Some(var_id) = &var.var_id {
             stack.add_var(*var_id, val.clone());
         }
     }
-    match eval_block(
+
+    match eval_block_fn(
         engine_state,
         stack,
         block,

crates/nu-cmd-extra/src/extra/strings/format/command.rs

@@ -1,8 +1,9 @@
 use std::vec;
 
-use nu_engine::{eval_expression, CallExt};
+use nu_engine::{get_eval_expression, CallExt};
 use nu_parser::parse_expression;
 use nu_protocol::ast::{Call, PathMember};
+
 use nu_protocol::engine::{Command, EngineState, Stack, StateWorkingSet};
 use nu_protocol::{
     Category, Example, ListStream, PipelineData, ShellError, Signature, Span, SyntaxShape, Type,
@@ -271,6 +272,7 @@ fn format_record(
 ) -> Result<String, ShellError> {
     let config = engine_state.get_config();
     let mut output = String::new();
+    let eval_expression = get_eval_expression(engine_state);
 
     for op in format_operations {
         match op {

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

@@ -1,5 +1,6 @@
-use nu_engine::{eval_block, redirect_env, CallExt};
+use nu_engine::{get_eval_block, redirect_env, CallExt};
 use nu_protocol::ast::Call;
+
 use nu_protocol::engine::{Closure, Command, EngineState, Stack};
 use nu_protocol::{
     Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, SyntaxShape, Type,
@@ -57,6 +58,8 @@ impl Command for Collect {
             }
         }
 
+        let eval_block = get_eval_block(engine_state);
+
         let result = eval_block(
             engine_state,
             &mut stack_captures,

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

@@ -1,7 +1,8 @@
 use std::thread;
 
-use nu_engine::{eval_block_with_early_return, redirect_env, CallExt};
+use nu_engine::{get_eval_block_with_early_return, redirect_env, CallExt};
 use nu_protocol::ast::Call;
+
 use nu_protocol::engine::{Closure, Command, EngineState, Stack};
 use nu_protocol::{
     Category, Example, IntoSpanned, ListStream, PipelineData, RawStream, ShellError, Signature,
@@ -116,6 +117,9 @@ impl Command for Do {
                 )
             }
         }
+
+        let eval_block_with_early_return = get_eval_block_with_early_return(engine_state);
+
         let result = eval_block_with_early_return(
             engine_state,
             &mut callee_stack,

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

@@ -1,5 +1,6 @@
-use nu_engine::{eval_block, eval_expression, CallExt};
+use nu_engine::{get_eval_block, get_eval_expression, CallExt};
 use nu_protocol::ast::Call;
+
 use nu_protocol::engine::{Block, Command, EngineState, Stack};
 use nu_protocol::{
     record, Category, Example, ListStream, PipelineData, ShellError, Signature, SyntaxShape, Type,
@@ -70,6 +71,10 @@ impl Command for For {
             .expect("checked through parser")
             .as_keyword()
             .expect("internal error: missing keyword");
+
+        let eval_expression = get_eval_expression(engine_state);
+        let eval_block = get_eval_block(engine_state);
+
         let values = eval_expression(engine_state, stack, keyword_expr)?;
 
         let block: Block = call.req(engine_state, stack, 2)?;
@@ -104,7 +109,6 @@ impl Command for For {
                         },
                     );
 
-                    //let block = engine_state.get_block(block_id);
                     match eval_block(
                         &engine_state,
                         stack,
@@ -150,7 +154,6 @@ impl Command for For {
                         },
                     );
 
-                    //let block = engine_state.get_block(block_id);
                     match eval_block(
                         &engine_state,
                         stack,

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

@@ -1,5 +1,6 @@
-use nu_engine::{eval_block, eval_expression, eval_expression_with_input, CallExt};
+use nu_engine::{get_eval_block, get_eval_expression, get_eval_expression_with_input, CallExt};
 use nu_protocol::ast::Call;
+
 use nu_protocol::engine::{Block, Command, EngineState, Stack, StateWorkingSet};
 use nu_protocol::eval_const::{eval_const_subexpression, eval_constant, eval_constant_with_input};
 use nu_protocol::{
@@ -105,6 +106,9 @@ impl Command for If {
         let cond = call.positional_nth(0).expect("checked through parser");
         let then_block: Block = call.req(engine_state, stack, 1)?;
         let else_case = call.positional_nth(2);
+        let eval_expression = get_eval_expression(engine_state);
+        let eval_expression_with_input = get_eval_expression_with_input(engine_state);
+        let eval_block = get_eval_block(engine_state);
 
         let result = eval_expression(engine_state, stack, cond)?;
         match &result {

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

@@ -4,6 +4,7 @@ use std::sync::{Arc, Mutex};
 
 use nu_engine::{eval_block, CallExt};
 use nu_protocol::ast::Call;
+use nu_protocol::debugger::WithoutDebug;
 use nu_protocol::engine::{Closure, Command, EngineState, Stack};
 use nu_protocol::{
     Category, Example, IntoPipelineData, LazyRecord, PipelineData, ShellError, Signature, Span,
@@ -146,7 +147,7 @@ impl<'a> LazyRecord<'a> for NuLazyRecord {
             }
         }
 
-        let pipeline_result = eval_block(
+        let pipeline_result = eval_block::<WithoutDebug>(
             &self.engine_state,
             &mut stack,
             block,

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

@@ -1,4 +1,4 @@
-use nu_engine::eval_block;
+use nu_engine::get_eval_block;
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::{
@@ -63,7 +63,7 @@ impl Command for Let {
             .expect("internal error: missing right hand side");
 
         let block = engine_state.get_block(block_id);
-
+        let eval_block = get_eval_block(engine_state);
         let pipeline_data = eval_block(engine_state, stack, block, input, true, false)?;
         let mut value = pipeline_data.into_value(call.head);
 

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

@@ -1,5 +1,6 @@
-use nu_engine::{eval_block, CallExt};
+use nu_engine::{get_eval_block, CallExt};
 use nu_protocol::ast::Call;
+
 use nu_protocol::engine::{Block, Command, EngineState, Stack};
 use nu_protocol::{
     Category, Example, PipelineData, ShellError, Signature, SyntaxShape, Type, Value,
@@ -33,6 +34,7 @@ impl Command for Loop {
         _input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
         let block: Block = call.req(engine_state, stack, 0)?;
+        let eval_block = get_eval_block(engine_state);
 
         loop {
             if nu_utils::ctrl_c::was_pressed(&engine_state.ctrlc) {
@@ -40,6 +42,7 @@ impl Command for Loop {
             }
 
             let block = engine_state.get_block(block.block_id);
+
             match eval_block(
                 engine_state,
                 stack,

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

@@ -1,5 +1,6 @@
-use nu_engine::{eval_block, eval_expression, eval_expression_with_input, CallExt};
+use nu_engine::{get_eval_block, get_eval_expression, get_eval_expression_with_input, CallExt};
 use nu_protocol::ast::{Call, Expr, Expression};
+
 use nu_protocol::engine::{Command, EngineState, Matcher, Stack};
 use nu_protocol::{
     Category, Example, PipelineData, ShellError, Signature, SyntaxShape, Type, Value,
@@ -38,6 +39,9 @@ impl Command for Match {
     ) -> Result<PipelineData, ShellError> {
         let value: Value = call.req(engine_state, stack, 0)?;
         let block = call.positional_nth(1);
+        let eval_expression = get_eval_expression(engine_state);
+        let eval_expression_with_input = get_eval_expression_with_input(engine_state);
+        let eval_block = get_eval_block(engine_state);
 
         if let Some(Expression {
             expr: Expr::MatchBlock(matches),

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

@@ -1,5 +1,6 @@
-use nu_engine::eval_block;
+use nu_engine::get_eval_block;
 use nu_protocol::ast::Call;
+
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::{
     Category, Example, PipelineData, ShellError, Signature, SyntaxShape, Type, Value,
@@ -63,6 +64,8 @@ impl Command for Mut {
             .expect("internal error: missing right hand side");
 
         let block = engine_state.get_block(block_id);
+        let eval_block = get_eval_block(engine_state);
+
         let pipeline_data = eval_block(
             engine_state,
             stack,

crates/nu-cmd-lang/src/core_commands/overlay/use_.rs

@@ -1,4 +1,4 @@
-use nu_engine::{eval_block, find_in_dirs_env, get_dirs_var_from_call, redirect_env, CallExt};
+use nu_engine::{find_in_dirs_env, get_dirs_var_from_call, get_eval_block, redirect_env, CallExt};
 use nu_parser::trim_quotes_str;
 use nu_protocol::ast::{Call, Expr};
 use nu_protocol::engine::{Command, EngineState, Stack};
@@ -141,6 +141,8 @@ impl Command for OverlayUse {
                     callee_stack.add_env_var("CURRENT_FILE".to_string(), file_path);
                 }
 
+                let eval_block = get_eval_block(engine_state);
+
                 let _ = eval_block(
                     engine_state,
                     &mut callee_stack,

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

@@ -1,5 +1,6 @@
-use nu_engine::{eval_block, CallExt};
+use nu_engine::{get_eval_block, CallExt, EvalBlockFn};
 use nu_protocol::ast::Call;
+
 use nu_protocol::engine::{Block, Closure, Command, EngineState, Stack};
 use nu_protocol::{
     record, Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, Span,
@@ -47,6 +48,7 @@ impl Command for Try {
         let catch_block: Option<Closure> = call.opt(engine_state, stack, 1)?;
 
         let try_block = engine_state.get_block(try_block.block_id);
+        let eval_block = get_eval_block(engine_state);
 
         let result = eval_block(engine_state, stack, try_block, input, false, false);
 
@@ -54,12 +56,12 @@ impl Command for Try {
             Err(error) => {
                 let error = intercept_block_control(error)?;
                 let err_record = err_to_record(error, call.head);
-                handle_catch(err_record, catch_block, engine_state, stack)
+                handle_catch(err_record, catch_block, engine_state, stack, eval_block)
             }
             Ok(PipelineData::Value(Value::Error { error, .. }, ..)) => {
                 let error = intercept_block_control(*error)?;
                 let err_record = err_to_record(error, call.head);
-                handle_catch(err_record, catch_block, engine_state, stack)
+                handle_catch(err_record, catch_block, engine_state, stack, eval_block)
             }
             // external command may fail to run
             Ok(pipeline) => {
@@ -69,7 +71,7 @@ impl Command for Try {
                     // (unless do -c is in effect)
                     // they can't be passed in as Nushell values.
                     let err_value = Value::nothing(call.head);
-                    handle_catch(err_value, catch_block, engine_state, stack)
+                    handle_catch(err_value, catch_block, engine_state, stack, eval_block)
                 } else {
                     Ok(pipeline)
                 }
@@ -98,6 +100,7 @@ fn handle_catch(
     catch_block: Option<Closure>,
     engine_state: &EngineState,
     stack: &mut Stack,
+    eval_block_fn: EvalBlockFn,
 ) -> Result<PipelineData, ShellError> {
     if let Some(catch_block) = catch_block {
         let catch_block = engine_state.get_block(catch_block.block_id);
@@ -108,7 +111,7 @@ fn handle_catch(
             }
         }
 
-        eval_block(
+        eval_block_fn(
             engine_state,
             stack,
             catch_block,

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

@@ -1,5 +1,6 @@
-use nu_engine::{eval_block, find_in_dirs_env, get_dirs_var_from_call, redirect_env};
+use nu_engine::{find_in_dirs_env, get_dirs_var_from_call, get_eval_block, redirect_env};
 use nu_protocol::ast::{Call, Expr, Expression};
+
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::{
     Category, Example, PipelineData, ShellError, Signature, SyntaxShape, Type, Value,
@@ -117,6 +118,8 @@ This command is a parser keyword. For details, check:
                     callee_stack.add_env_var("CURRENT_FILE".to_string(), file_path);
                 }
 
+                let eval_block = get_eval_block(engine_state);
+
                 // Run the block (discard the result)
                 let _ = eval_block(
                     engine_state,

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

@@ -1,5 +1,6 @@
-use nu_engine::{eval_block, eval_expression, CallExt};
+use nu_engine::{get_eval_block, get_eval_expression, CallExt};
 use nu_protocol::ast::Call;
+
 use nu_protocol::engine::{Block, Command, EngineState, Stack};
 use nu_protocol::{
     Category, Example, PipelineData, ShellError, Signature, SyntaxShape, Type, Value,
@@ -44,16 +45,21 @@ impl Command for While {
         let cond = call.positional_nth(0).expect("checked through parser");
         let block: Block = call.req(engine_state, stack, 1)?;
 
+        let eval_expression = get_eval_expression(engine_state);
+        let eval_block = get_eval_block(engine_state);
+
         loop {
             if nu_utils::ctrl_c::was_pressed(&engine_state.ctrlc) {
                 break;
             }
 
             let result = eval_expression(engine_state, stack, cond)?;
+
             match &result {
                 Value::Bool { val, .. } => {
                     if *val {
                         let block = engine_state.get_block(block.block_id);
+
                         match eval_block(
                             engine_state,
                             stack,

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

@@ -1,4 +1,5 @@
 use itertools::Itertools;
+use nu_protocol::debugger::WithoutDebug;
 use nu_protocol::{
     ast::{Block, RangeInclusion},
     engine::{EngineState, Stack, StateDelta, StateWorkingSet},
@@ -115,7 +116,8 @@ pub fn eval_block(
 
     stack.add_env_var("PWD".to_string(), Value::test_string(cwd.to_string_lossy()));
 
-    match nu_engine::eval_block(engine_state, &mut stack, &block, input, true, true) {
+    match nu_engine::eval_block::<WithoutDebug>(engine_state, &mut stack, &block, input, true, true)
+    {
         Err(err) => panic!("test eval error in `{}`: {:?}", "TODO", err),
         Ok(result) => result.into_value(Span::test_data()),
     }

crates/nu-color-config/src/style_computer.rs

@@ -8,6 +8,7 @@ use nu_protocol::{
 };
 use std::collections::HashMap;
 
+use nu_protocol::debugger::WithoutDebug;
 use std::fmt::{Debug, Formatter, Result};
 
 // ComputableStyle represents the valid user style types: a single color value, or a closure which
@@ -71,7 +72,7 @@ impl<'a> StyleComputer<'a> {
                         }
 
                         // Run the block.
-                        match eval_block(
+                        match eval_block::<WithoutDebug>(
                             self.engine_state,
                             &mut stack,
                             &block,

crates/nu-command/src/bytes/build_.rs

@@ -1,5 +1,6 @@
-use nu_engine::eval_expression;
+use nu_engine::get_eval_expression;
 use nu_protocol::ast::Call;
+
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::{
     Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, Span, SyntaxShape,
@@ -48,7 +49,10 @@ impl Command for BytesBuild {
         _input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
         let mut output = vec![];
-        for val in call.rest_iter_flattened(0, |expr| eval_expression(engine_state, stack, expr))? {
+        for val in call.rest_iter_flattened(0, |expr| {
+            let eval_expression = get_eval_expression(engine_state);
+            eval_expression(engine_state, stack, expr)
+        })? {
             match val {
                 Value::Binary { mut val, .. } => output.append(&mut val),
                 // Explicitly propagate errors instead of dropping them.

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

@@ -1,5 +1,6 @@
-use nu_engine::{eval_expression, CallExt};
+use nu_engine::{get_eval_expression, CallExt};
 use nu_protocol::ast::{Argument, Block, Call, Expr, Expression};
+
 use nu_protocol::engine::{Closure, Command, EngineState, Stack};
 use nu_protocol::{
     record, Category, Example, IntoInterruptiblePipelineData, PipelineData, ShellError, Signature,
@@ -43,7 +44,7 @@ impl Command for Explain {
         let ctrlc = engine_state.ctrlc.clone();
         let mut stack = stack.captures_to_stack(capture_block.captures);
 
-        let elements = get_pipeline_elements(engine_state, &mut stack, block)?;
+        let elements = get_pipeline_elements(engine_state, &mut stack, block, call.head)?;
 
         Ok(elements.into_pipeline_data(ctrlc))
     }
@@ -62,9 +63,11 @@ pub fn get_pipeline_elements(
     engine_state: &EngineState,
     stack: &mut Stack,
     block: &Block,
+    span: Span,
 ) -> Result<Vec<Value>, ShellError> {
     let mut element_values = vec![];
-    let span = Span::test_data();
+
+    let eval_expression = get_eval_expression(engine_state);
 
     for (pipeline_idx, pipeline) in block.pipelines.iter().enumerate() {
         let mut i = 0;
@@ -80,7 +83,7 @@ pub fn get_pipeline_elements(
                 let command = engine_state.get_decl(call.decl_id);
                 (
                     command.name().to_string(),
-                    get_arguments(engine_state, stack, *call),
+                    get_arguments(engine_state, stack, *call, eval_expression),
                 )
             } else {
                 ("no-op".to_string(), vec![])
@@ -106,7 +109,12 @@ pub fn get_pipeline_elements(
     Ok(element_values)
 }
 
-fn get_arguments(engine_state: &EngineState, stack: &mut Stack, call: Call) -> Vec<Value> {
+fn get_arguments(
+    engine_state: &EngineState,
+    stack: &mut Stack,
+    call: Call,
+    eval_expression_fn: fn(&EngineState, &mut Stack, &Expression) -> Result<Value, ShellError>,
+) -> Vec<Value> {
     let mut arg_value = vec![];
     let span = Span::test_data();
     for arg in &call.arguments {
@@ -145,8 +153,12 @@ fn get_arguments(engine_state: &EngineState, stack: &mut Stack, call: Call) -> V
                 };
 
                 if let Some(expression) = opt_expr {
-                    let evaluated_expression =
-                        get_expression_as_value(engine_state, stack, expression);
+                    let evaluated_expression = get_expression_as_value(
+                        engine_state,
+                        stack,
+                        expression,
+                        eval_expression_fn,
+                    );
                     let arg_type = "expr";
                     let arg_value_name = debug_string_without_formatting(&evaluated_expression);
                     let arg_value_type = &evaluated_expression.get_type().to_string();
@@ -166,7 +178,8 @@ fn get_arguments(engine_state: &EngineState, stack: &mut Stack, call: Call) -> V
             }
             Argument::Positional(inner_expr) => {
                 let arg_type = "positional";
-                let evaluated_expression = get_expression_as_value(engine_state, stack, inner_expr);
+                let evaluated_expression =
+                    get_expression_as_value(engine_state, stack, inner_expr, eval_expression_fn);
                 let arg_value_name = debug_string_without_formatting(&evaluated_expression);
                 let arg_value_type = &evaluated_expression.get_type().to_string();
                 let evaled_span = evaluated_expression.span();
@@ -184,7 +197,8 @@ fn get_arguments(engine_state: &EngineState, stack: &mut Stack, call: Call) -> V
             }
             Argument::Unknown(inner_expr) => {
                 let arg_type = "unknown";
-                let evaluated_expression = get_expression_as_value(engine_state, stack, inner_expr);
+                let evaluated_expression =
+                    get_expression_as_value(engine_state, stack, inner_expr, eval_expression_fn);
                 let arg_value_name = debug_string_without_formatting(&evaluated_expression);
                 let arg_value_type = &evaluated_expression.get_type().to_string();
                 let evaled_span = evaluated_expression.span();
@@ -202,7 +216,8 @@ fn get_arguments(engine_state: &EngineState, stack: &mut Stack, call: Call) -> V
             }
             Argument::Spread(inner_expr) => {
                 let arg_type = "spread";
-                let evaluated_expression = get_expression_as_value(engine_state, stack, inner_expr);
+                let evaluated_expression =
+                    get_expression_as_value(engine_state, stack, inner_expr, eval_expression_fn);
                 let arg_value_name = debug_string_without_formatting(&evaluated_expression);
                 let arg_value_type = &evaluated_expression.get_type().to_string();
                 let evaled_span = evaluated_expression.span();
@@ -228,8 +243,9 @@ fn get_expression_as_value(
     engine_state: &EngineState,
     stack: &mut Stack,
     inner_expr: &Expression,
+    eval_expression_fn: fn(&EngineState, &mut Stack, &Expression) -> Result<Value, ShellError>,
 ) -> Value {
-    match eval_expression(engine_state, stack, inner_expr) {
+    match eval_expression_fn(engine_state, stack, inner_expr) {
         Ok(v) => v,
         Err(error) => Value::error(error, inner_expr.span),
     }

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

@@ -5,6 +5,7 @@ mod info;
 mod inspect;
 mod inspect_table;
 mod metadata;
+mod profile;
 mod timeit;
 mod view;
 mod view_files;
@@ -18,6 +19,7 @@ pub use info::DebugInfo;
 pub use inspect::Inspect;
 pub use inspect_table::build_table;
 pub use metadata::Metadata;
+pub use profile::DebugProfile;
 pub use timeit::TimeIt;
 pub use view::View;
 pub use view_files::ViewFiles;

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

@@ -0,0 +1,169 @@
+use nu_engine::{eval_block_with_early_return, CallExt};
+use nu_protocol::ast::Call;
+use nu_protocol::debugger::{Profiler, WithDebug};
+use nu_protocol::engine::{Closure, Command, EngineState, Stack};
+use nu_protocol::{
+    Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, SyntaxShape, Type,
+};
+
+#[derive(Clone)]
+pub struct DebugProfile;
+
+impl Command for DebugProfile {
+    fn name(&self) -> &str {
+        "debug profile"
+    }
+
+    fn signature(&self) -> nu_protocol::Signature {
+        Signature::build("debug profile")
+            .required(
+                "closure",
+                SyntaxShape::Closure(None),
+                "The closure to profile.",
+            )
+            .switch("spans", "Collect spans of profiled elements", Some('s'))
+            .switch(
+                "expand-source",
+                "Collect full source fragments of profiled elements",
+                Some('e'),
+            )
+            .switch(
+                "values",
+                "Collect pipeline element output values",
+                Some('v'),
+            )
+            .switch("expr", "Collect expression types", Some('x'))
+            .named(
+                "max-depth",
+                SyntaxShape::Int,
+                "How many blocks/closures deep to step into (default 2)",
+                Some('m'),
+            )
+            .input_output_types(vec![(Type::Any, Type::Table(vec![]))])
+            .category(Category::Debug)
+    }
+
+    fn usage(&self) -> &str {
+        "Profile pipeline elements in a closure."
+    }
+
+    fn extra_usage(&self) -> &str {
+        r#"The profiler profiles every evaluated pipeline element inside a closure, stepping into all
+commands calls and other blocks/closures.
+
+The output can be heavily customized. By default, the following columns are included:
+- depth       : Depth of the pipeline element. Each entered block adds one level of depth. How many
+                blocks deep to step into is controlled with the --max-depth option.
+- id          : ID of the pipeline element
+- parent_id   : ID of the parent element
+- source      : Source code of the pipeline element. If the element has multiple lines, only the
+                first line is used and `...` is appended to the end. Full source code can be shown
+                with the  --expand-source flag.
+- duration_ms : How long it took to run the pipeline element in milliseconds.
+- (optional) span   : Span of the element. Can be viewed via the `view span` command. Enabled with
+                      the --spans flag.
+- (optional) expr   : The type of expression of the pipeline element. Enabled with the --expr flag.
+- (optional) output : The output value of the pipeline element. Enabled with the --values flag.
+
+To illustrate the depth and IDs, consider `debug profile { if true { echo 'spam' } }`. There are
+three pipeline elements:
+
+depth  id  parent_id
+    0   0          0  debug profile { do { if true { 'spam' } } }
+    1   1          0  if true { 'spam' }
+    2   2          1  'spam'
+
+Each block entered increments depth by 1 and each block left decrements it by one. This way you can
+control the profiling granularity. Passing --max-depth=1 to the above would stop at
+`if true { 'spam' }`. The id is used to identify each element. The parent_id tells you that 'spam'
+was spawned from `if true { 'spam' }` which was spawned from the root `debug profile { ... }`.
+
+Note: In some cases, the ordering of piepeline elements might not be intuitive. For example,
+`[ a bb cc ] | each { $in | str length }` involves some implicit collects and lazy evaluation
+confusing the id/parent_id hierarchy. The --expr flag is helpful for investigating these issues."#
+    }
+
+    fn run(
+        &self,
+        engine_state: &EngineState,
+        caller_stack: &mut Stack,
+        call: &Call,
+        input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        let closure: Closure = call.req(engine_state, caller_stack, 0)?;
+        let mut callee_stack = caller_stack.captures_to_stack(closure.captures);
+        let block = engine_state.get_block(closure.block_id);
+
+        let default_max_depth = 2;
+        let collect_spans = call.has_flag(engine_state, caller_stack, "spans")?;
+        let collect_expanded_source =
+            call.has_flag(engine_state, caller_stack, "expanded-source")?;
+        let collect_values = call.has_flag(engine_state, caller_stack, "values")?;
+        let collect_exprs = call.has_flag(engine_state, caller_stack, "expr")?;
+        let max_depth = call
+            .get_flag(engine_state, caller_stack, "max-depth")?
+            .unwrap_or(default_max_depth);
+
+        let profiler = Profiler::new(
+            max_depth,
+            collect_spans,
+            true,
+            collect_expanded_source,
+            collect_values,
+            collect_exprs,
+            call.span(),
+        );
+
+        let lock_err = {
+            |_| ShellError::GenericError {
+                error: "Profiler Error".to_string(),
+                msg: "could not lock debugger, poisoned mutex".to_string(),
+                span: Some(call.head),
+                help: None,
+                inner: vec![],
+            }
+        };
+
+        engine_state
+            .activate_debugger(Box::new(profiler))
+            .map_err(lock_err)?;
+
+        let result = eval_block_with_early_return::<WithDebug>(
+            engine_state,
+            &mut callee_stack,
+            block,
+            input,
+            call.redirect_stdout,
+            call.redirect_stdout,
+        );
+
+        // TODO: See eval_source()
+        match result {
+            Ok(pipeline_data) => {
+                let _ = pipeline_data.into_value(call.span());
+                // pipeline_data.print(engine_state, caller_stack, true, false)
+            }
+            Err(_e) => (), // TODO: Report error
+        }
+
+        let debugger = engine_state.deactivate_debugger().map_err(lock_err)?;
+        let res = debugger.report(engine_state, call.span());
+
+        res.map(|val| val.into_pipeline_data())
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![
+            Example {
+                description: "Profile config evaluation",
+                example: "debug profile { source $nu.config-path }",
+                result: None,
+            },
+            Example {
+                description: "Profile config evaluation with more granularity",
+                example: "debug profile { source $nu.config-path } --max-depth 4",
+                result: None,
+            },
+        ]
+    }
+}

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

@@ -1,4 +1,5 @@
-use nu_engine::{eval_block, eval_expression_with_input};
+use nu_engine::{get_eval_block, get_eval_expression_with_input};
+
 use nu_protocol::{
     ast::Call,
     engine::{Command, EngineState, Stack},
@@ -52,6 +53,7 @@ impl Command for TimeIt {
 
         if let Some(command_to_run) = command_to_run {
             if let Some(block_id) = command_to_run.as_block() {
+                let eval_block = get_eval_block(engine_state);
                 let block = engine_state.get_block(block_id);
                 eval_block(
                     engine_state,
@@ -62,6 +64,7 @@ impl Command for TimeIt {
                     call.redirect_stderr,
                 )?
             } else {
+                let eval_expression_with_input = get_eval_expression_with_input(engine_state);
                 eval_expression_with_input(
                     engine_state,
                     stack,

crates/nu-command/src/default_context.rs

@@ -140,6 +140,7 @@ pub fn add_shell_command_context(mut engine_state: EngineState) -> EngineState {
             Ast,
             Debug,
             DebugInfo,
+            DebugProfile,
             Explain,
             Inspect,
             Metadata,

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

@@ -1,4 +1,5 @@
-use nu_engine::{eval_block, redirect_env, CallExt};
+use nu_engine::{get_eval_block, redirect_env, CallExt};
+
 use nu_protocol::{
     ast::Call,
     engine::{Closure, Command, EngineState, Stack},
@@ -39,6 +40,8 @@ impl Command for ExportEnv {
         let block = engine_state.get_block(capture_block.block_id);
         let mut callee_stack = caller_stack.captures_to_stack(capture_block.captures);
 
+        let eval_block = get_eval_block(engine_state);
+
         let _ = eval_block(
             engine_state,
             &mut callee_stack,

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

@@ -1,9 +1,11 @@
 use std::path::PathBuf;
 
 use nu_engine::{
-    eval_block_with_early_return, find_in_dirs_env, get_dirs_var_from_call, redirect_env, CallExt,
+    find_in_dirs_env, get_dirs_var_from_call, get_eval_block_with_early_return, redirect_env,
+    CallExt,
 };
 use nu_protocol::ast::Call;
+
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::{
     Category, Example, PipelineData, ShellError, Signature, Spanned, SyntaxShape, Type, Value,
@@ -76,6 +78,8 @@ impl Command for SourceEnv {
         let block = engine_state.get_block(block_id as usize).clone();
         let mut callee_stack = caller_stack.gather_captures(engine_state, &block.captures);
 
+        let eval_block_with_early_return = get_eval_block_with_early_return(engine_state);
+
         let result = eval_block_with_early_return(
             engine_state,
             &mut callee_stack,

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

@@ -1,6 +1,7 @@
 use std::collections::HashMap;
 
 use nu_engine::{eval_block, CallExt};
+use nu_protocol::debugger::WithoutDebug;
 use nu_protocol::{
     ast::Call,
     engine::{Closure, Command, EngineState, Stack},
@@ -144,7 +145,7 @@ fn with_env(
         stack.add_env_var(k, v);
     }
 
-    eval_block(
+    eval_block::<WithoutDebug>(
         engine_state,
         &mut stack,
         block,

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

@@ -1,5 +1,5 @@
 use super::util::get_rest_for_glob_pattern;
-use nu_engine::{current_dir, eval_block, CallExt};
+use nu_engine::{current_dir, get_eval_block, CallExt};
 use nu_path::expand_to_real_path;
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
@@ -64,6 +64,7 @@ impl Command for Open {
         let ctrlc = engine_state.ctrlc.clone();
         let cwd = current_dir(engine_state, stack)?;
         let mut paths = get_rest_for_glob_pattern(engine_state, stack, call, 0)?;
+        let eval_block = get_eval_block(engine_state);
 
         if paths.is_empty() && call.rest_iter(0).next().is_none() {
             // try to use path from pipeline input if there were no positional or spread args

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

@@ -1,5 +1,5 @@
 use dialoguer::Input;
-use nu_engine::eval_expression;
+use nu_engine::get_eval_expression;
 use nu_protocol::ast::Expr;
 use nu_protocol::{
     ast::Call,
@@ -221,6 +221,7 @@ pub fn get_rest_for_glob_pattern(
     starting_pos: usize,
 ) -> Result<Vec<Spanned<NuGlob>>, ShellError> {
     let mut output = vec![];
+    let eval_expression = get_eval_expression(engine_state);
 
     for result in call.rest_iter_flattened(starting_pos, |expr| {
         let result = eval_expression(engine_state, stack, expr);
@@ -261,6 +262,7 @@ pub fn opt_for_glob_pattern(
     pos: usize,
 ) -> Result<Option<Spanned<NuGlob>>, ShellError> {
     if let Some(expr) = call.positional_nth(pos) {
+        let eval_expression = get_eval_expression(engine_state);
         let result = eval_expression(engine_state, stack, expr)?;
         let result_span = result.span();
         let result = match result {

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

@@ -9,8 +9,9 @@ use notify_debouncer_full::{
         EventKind, RecursiveMode, Watcher,
     },
 };
-use nu_engine::{current_dir, eval_block, CallExt};
+use nu_engine::{current_dir, get_eval_block, CallExt};
 use nu_protocol::ast::Call;
+
 use nu_protocol::engine::{Closure, Command, EngineState, Stack, StateWorkingSet};
 use nu_protocol::{
     format_error, Category, Example, IntoPipelineData, PipelineData, ShellError, Signature,
@@ -168,6 +169,8 @@ impl Command for Watch {
 
         eprintln!("Now watching files at {path:?}. Press ctrl+c to abort.");
 
+        let eval_block = get_eval_block(engine_state);
+
         let event_handler =
             |operation: &str, path: PathBuf, new_path: Option<PathBuf>| -> Result<(), ShellError> {
                 let glob_pattern = glob_pattern.clone();

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

@@ -1,12 +1,14 @@
-use super::utils::chain_error_with_input;
-use nu_engine::{eval_block_with_early_return, CallExt};
+use nu_engine::{get_eval_block_with_early_return, CallExt};
 use nu_protocol::ast::Call;
+
 use nu_protocol::engine::{Closure, Command, EngineState, Stack};
 use nu_protocol::{
     Category, Example, IntoInterruptiblePipelineData, IntoPipelineData, PipelineData, ShellError,
     Signature, Span, SyntaxShape, Type, Value,
 };
 
+use super::utils::chain_error_with_input;
+
 #[derive(Clone)]
 pub struct Each;
 
@@ -112,6 +114,8 @@ with 'transpose' first."#
         call: &Call,
         input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
+        let eval_block_with_early_return = get_eval_block_with_early_return(engine_state);
+
         let capture_block: Closure = call.req(engine_state, stack, 0)?;
 
         let keep_empty = call.has_flag(engine_state, stack, "keep-empty")?;
@@ -155,6 +159,8 @@ with 'transpose' first."#
                         x.into_pipeline_data(),
                         redirect_stdout,
                         redirect_stderr,
+                        // WithoutDebug,
+                        // &None,
                     ) {
                         Ok(v) => Some(v.into_value(span)),
                         Err(ShellError::Continue { span }) => Some(Value::nothing(span)),

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

@@ -1,6 +1,7 @@
 use super::utils::chain_error_with_input;
-use nu_engine::{eval_block, CallExt};
+use nu_engine::{get_eval_block, CallExt};
 use nu_protocol::ast::Call;
+
 use nu_protocol::engine::{Closure, Command, EngineState, Stack};
 use nu_protocol::{
     record, Category, Example, IntoInterruptiblePipelineData, IntoPipelineData, PipelineData,
@@ -63,6 +64,7 @@ a variable. On the other hand, the "row condition" syntax is not supported."#
         let span = call.head;
         let redirect_stdout = call.redirect_stdout;
         let redirect_stderr = call.redirect_stderr;
+        let eval_block = get_eval_block(&engine_state);
 
         match input {
             PipelineData::Empty => Ok(PipelineData::Empty),
@@ -162,6 +164,7 @@ a variable. On the other hand, the "row condition" syntax is not supported."#
                         stack.add_var(*var_id, x.clone());
                     }
                 }
+
                 Ok(match eval_block(
                     &engine_state,
                     &mut stack,

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

@@ -1,4 +1,4 @@
-use nu_engine::{eval_block, CallExt};
+use nu_engine::{get_eval_block, CallExt};
 use nu_protocol::ast::{Call, CellPath};
 use nu_protocol::engine::{Closure, Command, EngineState, Stack};
 use nu_protocol::{
@@ -238,12 +238,14 @@ fn group_closure(
 ) -> Result<IndexMap<String, Vec<Value>>, ShellError> {
     let error_key = "error";
     let mut groups: IndexMap<String, Vec<Value>> = IndexMap::new();
+    let eval_block = get_eval_block(engine_state);
 
     if let Some(capture_block) = &block {
         let block = engine_state.get_block(capture_block.block_id);
 
         for value in values {
             let mut stack = stack.captures_to_stack(capture_block.captures.clone());
+
             let pipeline = eval_block(
                 engine_state,
                 &mut stack,

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

@@ -1,5 +1,6 @@
-use nu_engine::{eval_block, CallExt};
+use nu_engine::{get_eval_block, CallExt, EvalBlockFn};
 use nu_protocol::ast::{Block, Call, CellPath, PathMember};
+
 use nu_protocol::engine::{Closure, Command, EngineState, Stack};
 use nu_protocol::{
     record, Category, Example, FromValue, IntoInterruptiblePipelineData, IntoPipelineData,
@@ -134,6 +135,8 @@ fn insert(
 
     let ctrlc = engine_state.ctrlc.clone();
 
+    let eval_block = get_eval_block(engine_state);
+
     match input {
         PipelineData::Value(mut value, metadata) => {
             if replacement.coerce_block().is_ok() {
@@ -155,6 +158,7 @@ fn insert(
                                 block,
                                 &cell_path.members,
                                 false,
+                                eval_block,
                             )?;
                         }
                     }
@@ -168,6 +172,7 @@ fn insert(
                             redirect_stderr,
                             &cell_path.members,
                             matches!(first, Some(PathMember::Int { .. })),
+                            eval_block,
                         )?;
                     }
                 }
@@ -242,6 +247,7 @@ fn insert(
                             redirect_stderr,
                             path,
                             true,
+                            eval_block,
                         )?;
                     } else {
                         value.insert_data_at_cell_path(path, replacement, span)?;
@@ -281,6 +287,7 @@ fn insert(
                             &block,
                             &cell_path.members,
                             false,
+                            eval_block,
                         );
 
                         if let Err(e) = err {
@@ -328,6 +335,7 @@ fn insert_value_by_closure(
     block: &Block,
     cell_path: &[PathMember],
     first_path_member_int: bool,
+    eval_block_fn: EvalBlockFn,
 ) -> Result<(), ShellError> {
     let input_at_path = value.clone().follow_cell_path(cell_path, false);
 
@@ -348,7 +356,7 @@ fn insert_value_by_closure(
         .map(IntoPipelineData::into_pipeline_data)
         .unwrap_or(PipelineData::Empty);
 
-    let output = eval_block(
+    let output = eval_block_fn(
         engine_state,
         stack,
         block,
@@ -370,6 +378,7 @@ fn insert_single_value_by_closure(
     redirect_stderr: bool,
     cell_path: &[PathMember],
     first_path_member_int: bool,
+    eval_block_fn: EvalBlockFn,
 ) -> Result<(), ShellError> {
     let span = replacement.span();
     let capture_block = Closure::from_value(replacement)?;
@@ -386,6 +395,7 @@ fn insert_single_value_by_closure(
         block,
         cell_path,
         first_path_member_int,
+        eval_block_fn,
     )
 }
 

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

@@ -1,6 +1,6 @@
 use std::{sync::mpsc, thread};
 
-use nu_engine::{eval_block_with_early_return, CallExt};
+use nu_engine::{get_eval_block_with_early_return, CallExt};
 use nu_protocol::{
     ast::Call,
     engine::{Closure, Command, EngineState, Stack},
@@ -118,6 +118,7 @@ interleave
         let (tx, rx) = mpsc::sync_channel(buffer_size);
 
         let closures: Vec<Closure> = call.rest(engine_state, stack, 0)?;
+        let eval_block_with_early_return = get_eval_block_with_early_return(engine_state);
 
         // Spawn the threads for the input and closure outputs
         (!input.is_nothing())

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

@@ -1,5 +1,6 @@
-use nu_engine::{eval_block_with_early_return, CallExt};
+use nu_engine::{get_eval_block_with_early_return, CallExt};
 use nu_protocol::ast::Call;
+
 use nu_protocol::engine::{Closure, Command, EngineState, Stack};
 use nu_protocol::{
     Category, Example, IntoInterruptiblePipelineData, PipelineData, ShellError, Signature, Span,
@@ -54,6 +55,7 @@ impl Command for Items {
         let orig_env_hidden = stack.env_hidden.clone();
         let span = call.head;
         let redirect_stderr = call.redirect_stderr;
+        let eval_block_with_early_return = get_eval_block_with_early_return(&engine_state);
 
         let input_span = input.span().unwrap_or(call.head);
         let run_for_each_item = move |keyval: (String, Value)| -> Option<Value> {

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

@@ -1,5 +1,6 @@
-use nu_engine::{eval_block_with_early_return, CallExt};
+use nu_engine::{get_eval_block_with_early_return, CallExt};
 use nu_protocol::ast::Call;
+
 use nu_protocol::engine::{Closure, Command, EngineState, Stack};
 use nu_protocol::{
     Category, Example, IntoInterruptiblePipelineData, IntoPipelineData, PipelineData, ShellError,
@@ -142,6 +143,8 @@ impl Command for ParEach {
             vec.into_iter().map(|(_, val)| val)
         };
 
+        let eval_block_with_early_return = get_eval_block_with_early_return(engine_state);
+
         match input {
             PipelineData::Empty => Ok(PipelineData::Empty),
             PipelineData::Value(Value::Range { val, .. }, ..) => Ok(create_pool(max_threads)?

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

@@ -1,6 +1,7 @@
-use nu_engine::{eval_block_with_early_return, CallExt};
+use nu_engine::{get_eval_block_with_early_return, CallExt};
 
 use nu_protocol::ast::Call;
+
 use nu_protocol::engine::{Closure, Command, EngineState, Stack};
 use nu_protocol::{
     Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, SyntaxShape, Type,
@@ -101,6 +102,7 @@ impl Command for Reduce {
         let mut stack = stack.captures_to_stack(capture_block.captures);
         let block = engine_state.get_block(capture_block.block_id);
         let ctrlc = engine_state.ctrlc.clone();
+        let eval_block_with_early_return = get_eval_block_with_early_return(engine_state);
 
         let orig_env_vars = stack.env_vars.clone();
         let orig_env_hidden = stack.env_hidden.clone();

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

@@ -1,6 +1,7 @@
 use indexmap::IndexMap;
-use nu_engine::{eval_block_with_early_return, CallExt};
+use nu_engine::{get_eval_block_with_early_return, CallExt};
 use nu_protocol::ast::Call;
+
 use nu_protocol::engine::{Closure, Command, EngineState, Stack};
 use nu_protocol::{
     record, Category, Example, IntoPipelineData, PipelineData, Record, ShellError, Signature,
@@ -156,6 +157,8 @@ fn rename(
     let columns: Vec<String> = call.rest(engine_state, stack, 0)?;
     let metadata = input.metadata();
 
+    let eval_block_with_early_return = get_eval_block_with_early_return(engine_state);
+
     let head_span = call.head;
     input
         .map(
@@ -176,6 +179,7 @@ fn rename(
                                         stack.add_var(*var_id, Value::string(c.clone(), span))
                                     }
                                 }
+
                                 let eval_result = eval_block_with_early_return(
                                     &engine_state,
                                     &mut stack,
@@ -184,6 +188,7 @@ fn rename(
                                     redirect_stdout,
                                     redirect_stderr,
                                 );
+
                                 match eval_result {
                                     Err(e) => return Value::error(e, span),
                                     Ok(res) => match res.collect_string_strict(span) {

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

@@ -1,4 +1,5 @@
-use nu_engine::{eval_block, CallExt};
+use nu_engine::{get_eval_block, CallExt};
+
 use nu_protocol::{
     ast::Call,
     engine::{Closure, Command, EngineState, Stack},
@@ -94,6 +95,8 @@ impl Command for SkipUntil {
         let redirect_stdout = call.redirect_stdout;
         let redirect_stderr = call.redirect_stderr;
 
+        let eval_block = get_eval_block(&engine_state);
+
         Ok(input
             .into_iter_strict(span)?
             .skip_while(move |value| {

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

@@ -1,4 +1,5 @@
-use nu_engine::{eval_block, CallExt};
+use nu_engine::{get_eval_block, CallExt};
+
 use nu_protocol::{
     ast::Call,
     engine::{Closure, Command, EngineState, Stack},
@@ -99,6 +100,8 @@ impl Command for SkipWhile {
         let redirect_stdout = call.redirect_stdout;
         let redirect_stderr = call.redirect_stderr;
 
+        let eval_block = get_eval_block(&engine_state);
+
         Ok(input
             .into_iter_strict(span)?
             .skip_while(move |value| {

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

@@ -1,4 +1,5 @@
-use nu_engine::{eval_block, CallExt};
+use nu_engine::{get_eval_block, CallExt};
+
 use nu_protocol::{
     ast::Call,
     engine::{Closure, Command, EngineState, Stack},
@@ -91,6 +92,8 @@ impl Command for TakeUntil {
         let redirect_stdout = call.redirect_stdout;
         let redirect_stderr = call.redirect_stderr;
 
+        let eval_block = get_eval_block(&engine_state);
+
         Ok(input
             .into_iter_strict(span)?
             .take_while(move |value| {

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

@@ -1,4 +1,4 @@
-use nu_engine::{eval_block, CallExt};
+use nu_engine::{get_eval_block, CallExt};
 use nu_protocol::{
     ast::Call,
     engine::{Closure, Command, EngineState, Stack},
@@ -91,6 +91,8 @@ impl Command for TakeWhile {
         let redirect_stdout = call.redirect_stdout;
         let redirect_stderr = call.redirect_stderr;
 
+        let eval_block = get_eval_block(&engine_state);
+
         Ok(input
             .into_iter_strict(span)?
             .take_while(move |value| {

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

@@ -1,6 +1,6 @@
 use std::{sync::mpsc, thread};
 
-use nu_engine::{eval_block_with_early_return, CallExt};
+use nu_engine::{get_eval_block_with_early_return, CallExt};
 use nu_protocol::{
     ast::Call,
     engine::{Closure, Command, EngineState, Stack},
@@ -83,6 +83,8 @@ use it in your pipeline."#
         let metadata = input.metadata();
         let metadata_clone = metadata.clone();
 
+        let eval_block_with_early_return = get_eval_block_with_early_return(engine_state);
+
         match input {
             // Handle external streams specially, to make sure they pass through
             PipelineData::ExternalStream {

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

@@ -1,5 +1,6 @@
-use nu_engine::{eval_block, CallExt};
+use nu_engine::{get_eval_block, CallExt, EvalBlockFn};
 use nu_protocol::ast::{Block, Call, CellPath, PathMember};
+
 use nu_protocol::engine::{Closure, Command, EngineState, Stack};
 use nu_protocol::{
     record, Category, Example, FromValue, IntoInterruptiblePipelineData, IntoPipelineData,
@@ -116,6 +117,8 @@ fn update(
 
     let ctrlc = engine_state.ctrlc.clone();
 
+    let eval_block = get_eval_block(engine_state);
+
     match input {
         PipelineData::Value(mut value, metadata) => {
             if replacement.coerce_block().is_ok() {
@@ -137,6 +140,7 @@ fn update(
                                 block,
                                 &cell_path.members,
                                 false,
+                                eval_block,
                             )?;
                         }
                     }
@@ -150,6 +154,7 @@ fn update(
                             redirect_stderr,
                             &cell_path.members,
                             matches!(first, Some(PathMember::Int { .. })),
+                            eval_block,
                         )?;
                     }
                 }
@@ -196,6 +201,7 @@ fn update(
                         redirect_stderr,
                         path,
                         true,
+                        eval_block,
                     )?;
                 } else {
                     value.update_data_at_cell_path(path, replacement)?;
@@ -228,6 +234,7 @@ fn update(
                             &block,
                             &cell_path.members,
                             false,
+                            eval_block,
                         );
 
                         if let Err(e) = err {
@@ -273,6 +280,7 @@ fn update_value_by_closure(
     block: &Block,
     cell_path: &[PathMember],
     first_path_member_int: bool,
+    eval_block_fn: EvalBlockFn,
 ) -> Result<(), ShellError> {
     let input_at_path = value.clone().follow_cell_path(cell_path, false)?;
 
@@ -289,7 +297,7 @@ fn update_value_by_closure(
         }
     }
 
-    let output = eval_block(
+    let output = eval_block_fn(
         engine_state,
         stack,
         block,
@@ -311,6 +319,7 @@ fn update_single_value_by_closure(
     redirect_stderr: bool,
     cell_path: &[PathMember],
     first_path_member_int: bool,
+    eval_block_fn: EvalBlockFn,
 ) -> Result<(), ShellError> {
     let span = replacement.span();
     let capture_block = Closure::from_value(replacement)?;
@@ -327,6 +336,7 @@ fn update_single_value_by_closure(
         block,
         cell_path,
         first_path_member_int,
+        eval_block_fn,
     )
 }
 

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

@@ -1,5 +1,6 @@
-use nu_engine::{eval_block, CallExt};
+use nu_engine::{get_eval_block, CallExt, EvalBlockFn};
 use nu_protocol::ast::{Block, Call, CellPath, PathMember};
+
 use nu_protocol::engine::{Closure, Command, EngineState, Stack};
 use nu_protocol::{
     record, Category, Example, FromValue, IntoInterruptiblePipelineData, IntoPipelineData,
@@ -158,6 +159,7 @@ fn upsert(
 
     let redirect_stdout = call.redirect_stdout;
     let redirect_stderr = call.redirect_stderr;
+    let eval_block = get_eval_block(engine_state);
 
     let ctrlc = engine_state.ctrlc.clone();
 
@@ -182,6 +184,7 @@ fn upsert(
                                 block,
                                 &cell_path.members,
                                 false,
+                                eval_block,
                             )?;
                         }
                     }
@@ -195,6 +198,7 @@ fn upsert(
                             redirect_stderr,
                             &cell_path.members,
                             matches!(first, Some(PathMember::Int { .. })),
+                            eval_block,
                         )?;
                     }
                 }
@@ -264,6 +268,7 @@ fn upsert(
                             redirect_stderr,
                             path,
                             true,
+                            eval_block,
                         )?;
                     } else {
                         value.upsert_data_at_cell_path(path, replacement)?;
@@ -303,6 +308,7 @@ fn upsert(
                             &block,
                             &cell_path.members,
                             false,
+                            eval_block,
                         );
 
                         if let Err(e) = err {
@@ -348,6 +354,7 @@ fn upsert_value_by_closure(
     block: &Block,
     cell_path: &[PathMember],
     first_path_member_int: bool,
+    eval_block_fn: EvalBlockFn,
 ) -> Result<(), ShellError> {
     let input_at_path = value.clone().follow_cell_path(cell_path, false);
 
@@ -368,7 +375,7 @@ fn upsert_value_by_closure(
         .map(IntoPipelineData::into_pipeline_data)
         .unwrap_or(PipelineData::Empty);
 
-    let output = eval_block(
+    let output = eval_block_fn(
         engine_state,
         stack,
         block,
@@ -390,6 +397,7 @@ fn upsert_single_value_by_closure(
     redirect_stderr: bool,
     cell_path: &[PathMember],
     first_path_member_int: bool,
+    eval_block_fn: EvalBlockFn,
 ) -> Result<(), ShellError> {
     let span = replacement.span();
     let capture_block = Closure::from_value(replacement)?;
@@ -406,6 +414,7 @@ fn upsert_single_value_by_closure(
         block,
         cell_path,
         first_path_member_int,
+        eval_block_fn,
     )
 }
 

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

@@ -1,4 +1,5 @@
-use nu_engine::{eval_block, CallExt};
+use nu_engine::{get_eval_block, CallExt};
+
 use nu_protocol::{
     ast::Call,
     engine::{Closure, EngineState, Stack},
@@ -40,6 +41,10 @@ pub fn boolean_fold(
 
     let ctrlc = engine_state.ctrlc.clone();
 
+    // TODO: This Clippy lint is incorrectly triggered in our CI for come reason
+    #[allow(clippy::needless_borrow)]
+    let eval_block = get_eval_block(&engine_state);
+
     for value in input.into_interruptible_iter(ctrlc) {
         // with_env() is used here to ensure that each iteration uses
         // a different set of environment variables.

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

@@ -1,5 +1,6 @@
-use nu_engine::{eval_block, CallExt};
+use nu_engine::{get_eval_block, CallExt};
 use nu_protocol::ast::Call;
+
 use nu_protocol::engine::{Closure, Command, EngineState, Stack};
 use nu_protocol::{
     record, Category, Example, IntoInterruptiblePipelineData, IntoPipelineData, PipelineData,
@@ -70,6 +71,9 @@ not supported."#
 
         let redirect_stdout = call.redirect_stdout;
         let redirect_stderr = call.redirect_stderr;
+
+        let eval_block = get_eval_block(&engine_state);
+
         Ok(input
             .into_iter_strict(span)?
             .filter_map(move |value| {
@@ -80,6 +84,7 @@ not supported."#
                         stack.add_var(*var_id, value.clone());
                     }
                 }
+
                 let result = eval_block(
                     &engine_state,
                     &mut stack,

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

@@ -1,4 +1,4 @@
-use nu_engine::{eval_block_with_early_return, CallExt};
+use nu_engine::{get_eval_block_with_early_return, CallExt};
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::{
@@ -102,6 +102,7 @@ impl Command for Zip {
         let head = call.head;
         let ctrlc = engine_state.ctrlc.clone();
         let metadata = input.metadata();
+        let eval_block_with_early_return = get_eval_block_with_early_return(engine_state);
 
         let other: PipelineData = match call.req(engine_state, stack, 0)? {
             // If a closure was provided, evaluate it and consume its stream output

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

@@ -1,5 +1,6 @@
 use itertools::unfold;
-use nu_engine::{eval_block_with_early_return, CallExt};
+use nu_engine::{get_eval_block_with_early_return, CallExt};
+
 use nu_protocol::{
     ast::Call,
     engine::{Closure, Command, EngineState, Stack},
@@ -107,6 +108,7 @@ used as the next argument to the closure, otherwise generation stops.
         let orig_env_hidden = stack.env_hidden.clone();
         let redirect_stdout = call.redirect_stdout;
         let redirect_stderr = call.redirect_stderr;
+        let eval_block_with_early_return = get_eval_block_with_early_return(&engine_state);
 
         // A type of Option<S> is used to represent state. Invocation
         // will stop on None. Using Option<S> allows functions to output

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

@@ -1,5 +1,6 @@
-use nu_engine::{eval_block_with_early_return, CallExt};
+use nu_engine::{get_eval_block_with_early_return, CallExt};
 use nu_protocol::ast::Call;
+
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::{Category, Example, PipelineData, ShellError, Signature, SyntaxShape, Type};
 
@@ -46,8 +47,10 @@ impl Command for Source {
         // Note: this hidden positional is the block_id that corresponded to the 0th position
         // it is put here by the parser
         let block_id: i64 = call.req_parser_info(engine_state, stack, "block_id")?;
-
         let block = engine_state.get_block(block_id as usize).clone();
+
+        let eval_block_with_early_return = get_eval_block_with_early_return(engine_state);
+
         eval_block_with_early_return(
             engine_state,
             stack,

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

@@ -1,6 +1,6 @@
 use nu_cmd_base::hook::eval_hook;
 use nu_engine::env_to_strings;
-use nu_engine::eval_expression;
+use nu_engine::get_eval_expression;
 use nu_engine::CallExt;
 use nu_protocol::IntoSpanned;
 use nu_protocol::NuGlob;
@@ -133,6 +133,8 @@ pub fn create_external_command(
             })
     }
 
+    let eval_expression = get_eval_expression(engine_state);
+
     let mut spanned_args = vec![];
     let mut arg_keep_raw = vec![];
     for (arg, spread) in call.rest_iter(1) {

crates/nu-engine/src/call_ext.rs

@@ -1,3 +1,4 @@
+use nu_protocol::debugger::WithoutDebug;
 use nu_protocol::{
     ast::Call,
     engine::{EngineState, Stack, StateWorkingSet},
@@ -69,7 +70,7 @@ impl CallExt for Call {
             if flag_name == name.0.item {
                 return if let Some(expr) = &name.2 {
                     // Check --flag=false
-                    let result = eval_expression(engine_state, stack, expr)?;
+                    let result = eval_expression::<WithoutDebug>(engine_state, stack, expr)?;
                     match result {
                         Value::Bool { val, .. } => Ok(val),
                         _ => Err(ShellError::CantConvert {
@@ -95,7 +96,7 @@ impl CallExt for Call {
         name: &str,
     ) -> Result<Option<T>, ShellError> {
         if let Some(expr) = self.get_flag_expr(name) {
-            let result = eval_expression(engine_state, stack, expr)?;
+            let result = eval_expression::<WithoutDebug>(engine_state, stack, expr)?;
             FromValue::from_value(result).map(Some)
         } else {
             Ok(None)
@@ -111,7 +112,7 @@ impl CallExt for Call {
         let mut output = vec![];
 
         for result in self.rest_iter_flattened(starting_pos, |expr| {
-            eval_expression(engine_state, stack, expr)
+            eval_expression::<WithoutDebug>(engine_state, stack, expr)
         })? {
             output.push(FromValue::from_value(result)?);
         }
@@ -126,7 +127,7 @@ impl CallExt for Call {
         pos: usize,
     ) -> Result<Option<T>, ShellError> {
         if let Some(expr) = self.positional_nth(pos) {
-            let result = eval_expression(engine_state, stack, expr)?;
+            let result = eval_expression::<WithoutDebug>(engine_state, stack, expr)?;
             FromValue::from_value(result).map(Some)
         } else {
             Ok(None)
@@ -153,7 +154,7 @@ impl CallExt for Call {
         pos: usize,
     ) -> Result<T, ShellError> {
         if let Some(expr) = self.positional_nth(pos) {
-            let result = eval_expression(engine_state, stack, expr)?;
+            let result = eval_expression::<WithoutDebug>(engine_state, stack, expr)?;
             FromValue::from_value(result)
         } else if self.positional_len() == 0 {
             Err(ShellError::AccessEmptyContent { span: self.head })
@@ -172,7 +173,7 @@ impl CallExt for Call {
         name: &str,
     ) -> Result<T, ShellError> {
         if let Some(expr) = self.get_parser_info(name) {
-            let result = eval_expression(engine_state, stack, expr)?;
+            let result = eval_expression::<WithoutDebug>(engine_state, stack, expr)?;
             FromValue::from_value(result)
         } else if self.parser_info.is_empty() {
             Err(ShellError::AccessEmptyContent { span: self.head })

crates/nu-engine/src/documentation.rs

@@ -1,4 +1,5 @@
 use nu_protocol::ast::{Argument, Expr, Expression, RecordItem};
+use nu_protocol::debugger::WithoutDebug;
 use nu_protocol::{
     ast::Call,
     engine::{EngineState, Stack},
@@ -235,7 +236,7 @@ fn get_documentation(
             }
 
             let mut caller_stack = Stack::new();
-            if let Ok(result) = eval_call(
+            if let Ok(result) = eval_call::<WithoutDebug>(
                 engine_state,
                 &mut caller_stack,
                 &Call {
@@ -347,7 +348,7 @@ fn get_ansi_color_for_component_or_default(
         // Call ansi command using argument
         if let Some(argument) = argument_opt {
             if let Some(decl_id) = engine_state.find_decl(b"ansi", &[]) {
-                if let Ok(result) = eval_call(
+                if let Ok(result) = eval_call::<WithoutDebug>(
                     engine_state,
                     &mut caller_stack,
                     &Call {

crates/nu-engine/src/env.rs

@@ -6,6 +6,7 @@ use nu_protocol::engine::{EngineState, Stack, StateWorkingSet, PWD_ENV};
 use nu_protocol::{Config, PipelineData, ShellError, Span, Value, VarId};
 
 use nu_path::canonicalize_with;
+use nu_protocol::debugger::WithoutDebug;
 
 use crate::eval_block;
 
@@ -388,7 +389,8 @@ fn get_converted_value(
                     }
 
                     let val_span = orig_val.span();
-                    let result = eval_block(
+                    // TODO DEBUG
+                    let result = eval_block::<WithoutDebug>(
                         engine_state,
                         &mut stack,
                         block,

crates/nu-engine/src/eval.rs

@@ -1,5 +1,6 @@
 use crate::{current_dir_str, get_config, get_full_help};
 use nu_path::expand_path_with;
+use nu_protocol::debugger::{DebugContext, WithoutDebug};
 use nu_protocol::{
     ast::{
         Argument, Assignment, Block, Call, Expr, Expression, ExternalArgument, PathMember,
@@ -10,10 +11,11 @@ use nu_protocol::{
     Config, DeclId, IntoPipelineData, IntoSpanned, PipelineData, RawStream, ShellError, Span,
     Spanned, Type, Value, VarId, ENV_VARIABLE_ID,
 };
+
 use std::thread::{self, JoinHandle};
 use std::{borrow::Cow, collections::HashMap};
 
-pub fn eval_call(
+pub fn eval_call<D: DebugContext>(
     engine_state: &EngineState,
     caller_stack: &mut Stack,
     call: &Call,
@@ -75,7 +77,7 @@ pub fn eval_call(
                 .expect("internal error: all custom parameters must have var_ids");
 
             if let Some(arg) = call.positional_nth(param_idx) {
-                let result = eval_expression(engine_state, caller_stack, arg)?;
+                let result = eval_expression::<D>(engine_state, caller_stack, arg)?;
                 let param_type = param.shape.to_type();
                 if required && !result.get_type().is_subtype(&param_type) {
                     // need to check if result is an empty list, and param_type is table or list
@@ -110,7 +112,7 @@ pub fn eval_call(
             for result in call.rest_iter_flattened(
                 decl.signature().required_positional.len()
                     + decl.signature().optional_positional.len(),
-                |expr| eval_expression(engine_state, caller_stack, expr),
+                |expr| eval_expression::<D>(engine_state, caller_stack, expr),
             )? {
                 rest_items.push(result);
             }
@@ -136,7 +138,7 @@ pub fn eval_call(
                     if let (Some(spanned), Some(short)) = (&call_named.1, named.short) {
                         if spanned.item == short.to_string() {
                             if let Some(arg) = &call_named.2 {
-                                let result = eval_expression(engine_state, caller_stack, arg)?;
+                                let result = eval_expression::<D>(engine_state, caller_stack, arg)?;
 
                                 callee_stack.add_var(var_id, result);
                             } else if let Some(value) = &named.default_value {
@@ -148,7 +150,7 @@ pub fn eval_call(
                         }
                     } else if call_named.0.item == named.long {
                         if let Some(arg) = &call_named.2 {
-                            let result = eval_expression(engine_state, caller_stack, arg)?;
+                            let result = eval_expression::<D>(engine_state, caller_stack, arg)?;
 
                             callee_stack.add_var(var_id, result);
                         } else if let Some(value) = &named.default_value {
@@ -172,7 +174,7 @@ pub fn eval_call(
             }
         }
 
-        let result = eval_block_with_early_return(
+        let result = eval_block_with_early_return::<D>(
             engine_state,
             &mut callee_stack,
             block,
@@ -293,12 +295,12 @@ fn eval_external(
     command.run(engine_state, stack, &call, input)
 }
 
-pub fn eval_expression(
+pub fn eval_expression<D: DebugContext>(
     engine_state: &EngineState,
     stack: &mut Stack,
     expr: &Expression,
 ) -> Result<Value, ShellError> {
-    <EvalRuntime as Eval>::eval(engine_state, stack, expr)
+    <EvalRuntime as Eval>::eval::<D>(engine_state, stack, expr)
 }
 
 /// Checks the expression to see if it's a internal or external call. If so, passes the input
@@ -307,7 +309,7 @@ pub fn eval_expression(
 ///
 /// It returns PipelineData with a boolean flag, indicating if the external failed to run.
 /// The boolean flag **may only be true** for external calls, for internal calls, it always to be false.
-pub fn eval_expression_with_input(
+pub fn eval_expression_with_input<D: DebugContext>(
     engine_state: &EngineState,
     stack: &mut Stack,
     expr: &Expression,
@@ -325,9 +327,9 @@ pub fn eval_expression_with_input(
                 let mut call = call.clone();
                 call.redirect_stdout = redirect_stdout;
                 call.redirect_stderr = redirect_stderr;
-                input = eval_call(engine_state, stack, &call, input)?;
+                input = eval_call::<D>(engine_state, stack, &call, input)?;
             } else {
-                input = eval_call(engine_state, stack, call, input)?;
+                input = eval_call::<D>(engine_state, stack, call, input)?;
             }
         }
         Expression {
@@ -352,7 +354,7 @@ pub fn eval_expression_with_input(
             let block = engine_state.get_block(*block_id);
 
             // FIXME: protect this collect with ctrl-c
-            input = eval_subexpression(engine_state, stack, block, input)?;
+            input = eval_subexpression::<D>(engine_state, stack, block, input)?;
         }
 
         elem @ Expression {
@@ -367,19 +369,19 @@ pub fn eval_expression_with_input(
                 let block = engine_state.get_block(*block_id);
 
                 // FIXME: protect this collect with ctrl-c
-                input = eval_subexpression(engine_state, stack, block, input)?;
+                input = eval_subexpression::<D>(engine_state, stack, block, input)?;
                 let value = input.into_value(*span);
                 input = value
                     .follow_cell_path(&full_cell_path.tail, false)?
                     .into_pipeline_data()
             }
             _ => {
-                input = eval_expression(engine_state, stack, elem)?.into_pipeline_data();
+                input = eval_expression::<D>(engine_state, stack, elem)?.into_pipeline_data();
             }
         },
 
         elem => {
-            input = eval_expression(engine_state, stack, elem)?.into_pipeline_data();
+            input = eval_expression::<D>(engine_state, stack, elem)?.into_pipeline_data();
         }
     };
 
@@ -406,7 +408,7 @@ fn might_consume_external_result(input: PipelineData) -> (PipelineData, bool) {
 }
 
 #[allow(clippy::too_many_arguments)]
-fn eval_element_with_input(
+fn eval_element_with_input<D: DebugContext>(
     engine_state: &EngineState,
     stack: &mut Stack,
     element: &PipelineElement,
@@ -416,7 +418,9 @@ fn eval_element_with_input(
     redirect_combine: bool,
     stderr_writer_jobs: &mut Vec<DataSaveJob>,
 ) -> Result<(PipelineData, bool), ShellError> {
-    match element {
+    D::enter_element(engine_state, element);
+
+    let result = match element {
         PipelineElement::Expression(pipe_span, expr)
         | PipelineElement::OutErrPipedExpression(pipe_span, expr) => {
             if matches!(element, PipelineElement::OutErrPipedExpression(..))
@@ -446,7 +450,7 @@ fn eval_element_with_input(
                     )?;
                     Ok(might_consume_external_result(result))
                 }
-                _ => eval_expression_with_input(
+                _ => eval_expression_with_input::<D>(
                     engine_state,
                     stack,
                     expr,
@@ -483,7 +487,7 @@ fn eval_element_with_input(
                     })
                 }
             };
-            eval_expression_with_input(
+            eval_expression_with_input::<D>(
                 engine_state,
                 stack,
                 expr,
@@ -514,7 +518,7 @@ fn eval_element_with_input(
                         );
                         match result_out_stream {
                             None => {
-                                eval_call(engine_state, stack, &save_call, input).map(|_| {
+                                eval_call::<D>(engine_state, stack, &save_call, input).map(|_| {
                                     // save is internal command, normally it exists with non-ExternalStream
                                     // but here in redirection context, we make it returns ExternalStream
                                     // So nu handles exit_code correctly
@@ -602,7 +606,7 @@ fn eval_element_with_input(
                         Some((*err_span, err_expr.clone(), *err_append_mode)),
                     );
 
-                    eval_call(engine_state, stack, &save_call, input).map(|_| {
+                    eval_call::<D>(engine_state, stack, &save_call, input).map(|_| {
                         // save is internal command, normally it exists with non-ExternalStream
                         // but here in redirection context, we make it returns ExternalStream
                         // So nu handles exit_code correctly
@@ -648,7 +652,7 @@ fn eval_element_with_input(
                 }
                 _ => {
                     // we need to redirect output, so the result can be saved and pass to `save` command.
-                    eval_element_with_input(
+                    eval_element_with_input::<D>(
                         engine_state,
                         stack,
                         &PipelineElement::Expression(*cmd_span, cmd_exp.clone()),
@@ -661,7 +665,7 @@ fn eval_element_with_input(
                     .map(|x| x.0)?
                 }
             };
-            eval_element_with_input(
+            eval_element_with_input::<D>(
                 engine_state,
                 stack,
                 &PipelineElement::Redirection(
@@ -677,7 +681,7 @@ fn eval_element_with_input(
                 stderr_writer_jobs,
             )
         }
-        PipelineElement::And(_, expr) => eval_expression_with_input(
+        PipelineElement::And(_, expr) => eval_expression_with_input::<D>(
             engine_state,
             stack,
             expr,
@@ -685,7 +689,7 @@ fn eval_element_with_input(
             redirect_stdout,
             redirect_stderr,
         ),
-        PipelineElement::Or(_, expr) => eval_expression_with_input(
+        PipelineElement::Or(_, expr) => eval_expression_with_input::<D>(
             engine_state,
             stack,
             expr,
@@ -693,7 +697,11 @@ fn eval_element_with_input(
             redirect_stdout,
             redirect_stderr,
         ),
-    }
+    };
+
+    D::leave_element(engine_state, element, &result);
+
+    result
 }
 
 // In redirection context, if nushell gets an ExternalStream
@@ -836,7 +844,7 @@ fn is_redirect_combine_required(elements: &[PipelineElement], idx: usize) -> boo
         )
 }
 
-pub fn eval_block_with_early_return(
+pub fn eval_block_with_early_return<D: DebugContext>(
     engine_state: &EngineState,
     stack: &mut Stack,
     block: &Block,
@@ -844,7 +852,7 @@ pub fn eval_block_with_early_return(
     redirect_stdout: bool,
     redirect_stderr: bool,
 ) -> Result<PipelineData, ShellError> {
-    match eval_block(
+    match eval_block::<D>(
         engine_state,
         stack,
         block,
@@ -857,7 +865,7 @@ pub fn eval_block_with_early_return(
     }
 }
 
-pub fn eval_block(
+pub fn eval_block<D: DebugContext>(
     engine_state: &EngineState,
     stack: &mut Stack,
     block: &Block,
@@ -865,6 +873,8 @@ pub fn eval_block(
     redirect_stdout: bool,
     redirect_stderr: bool,
 ) -> Result<PipelineData, ShellError> {
+    D::enter_block(engine_state, block);
+
     let num_pipelines = block.len();
 
     for (pipeline_idx, pipeline) in block.pipelines.iter().enumerate() {
@@ -891,7 +901,7 @@ pub fn eval_block(
             let redirect_combine = is_redirect_combine_required(elements, idx);
 
             // if eval internal command failed, it can just make early return with `Err(ShellError)`.
-            let eval_result = eval_element_with_input(
+            let eval_result = eval_element_with_input::<D>(
                 engine_state,
                 stack,
                 element,
@@ -962,16 +972,18 @@ pub fn eval_block(
         }
     }
 
+    D::leave_block(engine_state, block);
+
     Ok(input)
 }
 
-pub fn eval_subexpression(
+pub fn eval_subexpression<D: DebugContext>(
     engine_state: &EngineState,
     stack: &mut Stack,
     block: &Block,
     input: PipelineData,
 ) -> Result<PipelineData, ShellError> {
-    eval_block(engine_state, stack, block, input, true, false)
+    eval_block::<D>(engine_state, stack, block, input, true, false)
 }
 
 pub fn eval_variable(
@@ -1096,7 +1108,8 @@ impl DataSaveJob {
             inner: thread::Builder::new()
                 .name("stderr saver".to_string())
                 .spawn(move || {
-                    let result = eval_call(&engine_state, &mut stack, &save_call, input);
+                    let result =
+                        eval_call::<WithoutDebug>(&engine_state, &mut stack, &save_call, input);
                     if let Err(err) = result {
                         eprintln!("WARNING: error occurred when redirect to stderr: {:?}", err);
                     }
@@ -1166,14 +1179,14 @@ impl Eval for EvalRuntime {
         eval_variable(engine_state, stack, var_id, span)
     }
 
-    fn eval_call(
+    fn eval_call<D: DebugContext>(
         engine_state: &EngineState,
         stack: &mut Stack,
         call: &Call,
         _: Span,
     ) -> Result<Value, ShellError> {
         // FIXME: protect this collect with ctrl-c
-        Ok(eval_call(engine_state, stack, call, PipelineData::empty())?.into_value(call.head))
+        Ok(eval_call::<D>(engine_state, stack, call, PipelineData::empty())?.into_value(call.head))
     }
 
     fn eval_external_call(
@@ -1198,7 +1211,7 @@ impl Eval for EvalRuntime {
         .into_value(span))
     }
 
-    fn eval_subexpression(
+    fn eval_subexpression<D: DebugContext>(
         engine_state: &EngineState,
         stack: &mut Stack,
         block_id: usize,
@@ -1207,7 +1220,10 @@ impl Eval for EvalRuntime {
         let block = engine_state.get_block(block_id);
 
         // FIXME: protect this collect with ctrl-c
-        Ok(eval_subexpression(engine_state, stack, block, PipelineData::empty())?.into_value(span))
+        Ok(
+            eval_subexpression::<D>(engine_state, stack, block, PipelineData::empty())?
+                .into_value(span),
+        )
     }
 
     fn regex_match(
@@ -1221,7 +1237,7 @@ impl Eval for EvalRuntime {
         lhs.regex_match(engine_state, op_span, rhs, invert, expr_span)
     }
 
-    fn eval_assignment(
+    fn eval_assignment<D: DebugContext>(
         engine_state: &EngineState,
         stack: &mut Stack,
         lhs: &Expression,
@@ -1230,28 +1246,28 @@ impl Eval for EvalRuntime {
         op_span: Span,
         _expr_span: Span,
     ) -> Result<Value, ShellError> {
-        let rhs = eval_expression(engine_state, stack, rhs)?;
+        let rhs = eval_expression::<D>(engine_state, stack, rhs)?;
 
         let rhs = match assignment {
             Assignment::Assign => rhs,
             Assignment::PlusAssign => {
-                let lhs = eval_expression(engine_state, stack, lhs)?;
+                let lhs = eval_expression::<D>(engine_state, stack, lhs)?;
                 lhs.add(op_span, &rhs, op_span)?
             }
             Assignment::MinusAssign => {
-                let lhs = eval_expression(engine_state, stack, lhs)?;
+                let lhs = eval_expression::<D>(engine_state, stack, lhs)?;
                 lhs.sub(op_span, &rhs, op_span)?
             }
             Assignment::MultiplyAssign => {
-                let lhs = eval_expression(engine_state, stack, lhs)?;
+                let lhs = eval_expression::<D>(engine_state, stack, lhs)?;
                 lhs.mul(op_span, &rhs, op_span)?
             }
             Assignment::DivideAssign => {
-                let lhs = eval_expression(engine_state, stack, lhs)?;
+                let lhs = eval_expression::<D>(engine_state, stack, lhs)?;
                 lhs.div(op_span, &rhs, op_span)?
             }
             Assignment::AppendAssign => {
-                let lhs = eval_expression(engine_state, stack, lhs)?;
+                let lhs = eval_expression::<D>(engine_state, stack, lhs)?;
                 lhs.append(op_span, &rhs, op_span)?
             }
         };
@@ -1273,7 +1289,8 @@ impl Eval for EvalRuntime {
                         // As such, give it special treatment here.
                         let is_env = var_id == &ENV_VARIABLE_ID;
                         if is_env || engine_state.get_var(*var_id).mutable {
-                            let mut lhs = eval_expression(engine_state, stack, &cell_path.head)?;
+                            let mut lhs =
+                                eval_expression::<D>(engine_state, stack, &cell_path.head)?;
 
                             lhs.upsert_data_at_cell_path(&cell_path.tail, rhs)?;
                             if is_env {

crates/nu-engine/src/eval_helpers.rs

@@ -0,0 +1,95 @@
+use crate::{
+    eval_block, eval_block_with_early_return, eval_expression, eval_expression_with_input,
+    eval_subexpression,
+};
+use nu_protocol::ast::{Block, Expression};
+use nu_protocol::debugger::{WithDebug, WithoutDebug};
+use nu_protocol::engine::{EngineState, Stack};
+use nu_protocol::{PipelineData, ShellError, Value};
+
+/// Type of eval_block() function
+pub type EvalBlockFn = fn(
+    &EngineState,
+    &mut Stack,
+    &Block,
+    PipelineData,
+    bool,
+    bool,
+) -> Result<PipelineData, ShellError>;
+
+/// Type of eval_block_with_early_return() function
+pub type EvalBlockWithEarlyReturnFn = fn(
+    &EngineState,
+    &mut Stack,
+    &Block,
+    PipelineData,
+    bool,
+    bool,
+) -> Result<PipelineData, ShellError>;
+
+/// Type of eval_expression() function
+pub type EvalExpressionFn = fn(&EngineState, &mut Stack, &Expression) -> Result<Value, ShellError>;
+
+/// Type of eval_expression_with_input() function
+pub type EvalExpressionWithInputFn = fn(
+    &EngineState,
+    &mut Stack,
+    &Expression,
+    PipelineData,
+    bool,
+    bool,
+) -> Result<(PipelineData, bool), ShellError>;
+
+/// Type of eval_subexpression() function
+pub type EvalSubexpressionFn =
+    fn(&EngineState, &mut Stack, &Block, PipelineData) -> Result<PipelineData, ShellError>;
+
+/// Helper function to fetch `eval_block()` with the correct type parameter based on whether
+/// engine_state is configured with or without a debugger.
+pub fn get_eval_block(engine_state: &EngineState) -> EvalBlockFn {
+    if engine_state.is_debugging() {
+        eval_block::<WithDebug>
+    } else {
+        eval_block::<WithoutDebug>
+    }
+}
+
+/// Helper function to fetch `eval_block_with_early_return()` with the correct type parameter based
+/// on whether engine_state is configured with or without a debugger.
+pub fn get_eval_block_with_early_return(engine_state: &EngineState) -> EvalBlockWithEarlyReturnFn {
+    if engine_state.is_debugging() {
+        eval_block_with_early_return::<WithDebug>
+    } else {
+        eval_block_with_early_return::<WithoutDebug>
+    }
+}
+
+/// Helper function to fetch `eval_expression()` with the correct type parameter based on whether
+/// engine_state is configured with or without a debugger.
+pub fn get_eval_expression(engine_state: &EngineState) -> EvalExpressionFn {
+    if engine_state.is_debugging() {
+        eval_expression::<WithDebug>
+    } else {
+        eval_expression::<WithoutDebug>
+    }
+}
+
+/// Helper function to fetch `eval_expression_with_input()` with the correct type parameter based
+/// on whether engine_state is configured with or without a debugger.
+pub fn get_eval_expression_with_input(engine_state: &EngineState) -> EvalExpressionWithInputFn {
+    if engine_state.is_debugging() {
+        eval_expression_with_input::<WithDebug>
+    } else {
+        eval_expression_with_input::<WithoutDebug>
+    }
+}
+
+/// Helper function to fetch `eval_subexpression()` with the correct type parameter based on whether
+/// engine_state is configured with or without a debugger.
+pub fn get_eval_subexpression(engine_state: &EngineState) -> EvalSubexpressionFn {
+    if engine_state.is_debugging() {
+        eval_subexpression::<WithDebug>
+    } else {
+        eval_subexpression::<WithoutDebug>
+    }
+}

crates/nu-engine/src/lib.rs

@@ -3,6 +3,7 @@ pub mod column;
 pub mod documentation;
 pub mod env;
 mod eval;
+mod eval_helpers;
 mod glob_from;
 pub mod scope;
 
@@ -14,4 +15,5 @@ pub use eval::{
     eval_block, eval_block_with_early_return, eval_call, eval_expression,
     eval_expression_with_input, eval_subexpression, eval_variable, redirect_env,
 };
+pub use eval_helpers::*;
 pub use glob_from::glob_from;

crates/nu-explore/src/nu_common/command.rs

@@ -1,5 +1,6 @@
 use nu_engine::eval_block;
 use nu_parser::parse;
+use nu_protocol::debugger::WithoutDebug;
 use nu_protocol::{
     engine::{EngineState, Stack, StateWorkingSet},
     PipelineData, ShellError, Value,
@@ -90,5 +91,5 @@ fn eval_source2(
         block.pipelines.drain(..block.pipelines.len() - 1);
     }
 
-    eval_block(engine_state, stack, &block, input, true, true)
+    eval_block::<WithoutDebug>(engine_state, stack, &block, input, true, true)
 }

crates/nu-plugin/src/plugin/declaration.rs

@@ -3,7 +3,8 @@ use crate::protocol::{CallInfo, EvaluatedCall};
 use std::path::{Path, PathBuf};
 use std::sync::Arc;
 
-use nu_engine::eval_block;
+use nu_engine::{get_eval_block, get_eval_expression};
+
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::{ast::Call, PluginSignature, Signature};
 use nu_protocol::{Example, PipelineData, ShellError, Value};
@@ -71,9 +72,13 @@ impl Command for PluginDeclaration {
         call: &Call,
         input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
+        let eval_block = get_eval_block(engine_state);
+        let eval_expression = get_eval_expression(engine_state);
+
         // Create the EvaluatedCall to send to the plugin first - it's best for this to fail early,
         // before we actually try to run the plugin command
-        let evaluated_call = EvaluatedCall::try_from_call(call, engine_state, stack)?;
+        let evaluated_call =
+            EvaluatedCall::try_from_call(call, engine_state, stack, eval_expression)?;
 
         // Fetch the configuration for a plugin
         //

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

@@ -1,4 +1,5 @@
-use nu_engine::eval_expression;
+use nu_protocol::ast::Expression;
+
 use nu_protocol::{
     ast::Call,
     engine::{EngineState, Stack},
@@ -32,15 +33,16 @@ impl EvaluatedCall {
         call: &Call,
         engine_state: &EngineState,
         stack: &mut Stack,
+        eval_expression_fn: fn(&EngineState, &mut Stack, &Expression) -> Result<Value, ShellError>,
     ) -> Result<Self, ShellError> {
         let positional =
-            call.rest_iter_flattened(0, |expr| eval_expression(engine_state, stack, expr))?;
+            call.rest_iter_flattened(0, |expr| eval_expression_fn(engine_state, stack, expr))?;
 
         let mut named = Vec::with_capacity(call.named_len());
         for (string, _, expr) in call.named_iter() {
             let value = match expr {
                 None => None,
-                Some(expr) => Some(eval_expression(engine_state, stack, expr)?),
+                Some(expr) => Some(eval_expression_fn(engine_state, stack, expr)?),
             };
 
             named.push((string.clone(), value))

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

@@ -0,0 +1,149 @@
+//! Traits related to debugging
+//!
+//! The purpose of DebugContext is achieving static dispatch on `eval_xxx()` calls.
+//! The main Debugger trait is intended to be used as a trait object.
+//!
+//! The debugging information is stored in `EngineState` as the `debugger` field storing a `Debugger`
+//! trait object behind `Arc` and `Mutex`. To evaluate something (e.g., a block), first create a
+//! `Debugger` trait object (such as the `Profiler`). Then, add it to engine state via
+//! `engine_state.activate_debugger()`. This sets the internal state of EngineState to the debugging
+//! mode and calls `Debugger::activate()`. Now, you can call `eval_xxx::<WithDebug>()`. When you're
+//! done, call `engine_state.deactivate_debugger()` which calls `Debugger::deactivate()`, sets the
+//! EngineState into non-debugging mode, and returns the original mutated `Debugger` trait object.
+//! (`NoopDebugger` is placed in its place inside `EngineState`.) After deactivating, you can call
+//! `Debugger::report()` to get some output from the debugger, if necessary.
+
+use crate::ast::{Block, PipelineElement};
+use crate::engine::EngineState;
+use crate::{PipelineData, ShellError, Span, Value};
+use std::fmt::Debug;
+use std::ops::DerefMut;
+
+/// Trait used for static dispatch of `eval_xxx()` evaluator calls
+///
+/// DebugContext implements the same interface as Debugger (except activate() and deactivate(). It
+/// is intended to be implemented only by two structs
+/// * WithDebug which calls down to the Debugger methods
+/// * WithoutDebug with default implementation, i.e., empty calls to be optimized away
+pub trait DebugContext: Clone + Copy + Debug {
+    /// Called when the evaluator enters a block
+    #[allow(unused_variables)]
+    fn enter_block(engine_state: &EngineState, block: &Block) {}
+
+    /// Called when the evaluator leaves a block
+    #[allow(unused_variables)]
+    fn leave_block(engine_state: &EngineState, block: &Block) {}
+
+    /// Called when the evaluator enters a pipeline element
+    #[allow(unused_variables)]
+    fn enter_element(engine_state: &EngineState, element: &PipelineElement) {}
+
+    /// Called when the evaluator leaves a pipeline element
+    #[allow(unused_variables)]
+    fn leave_element(
+        engine_state: &EngineState,
+        element: &PipelineElement,
+        result: &Result<(PipelineData, bool), ShellError>,
+    ) {
+    }
+}
+
+/// Marker struct signalizing that evaluation should use a Debugger
+///
+/// Trait methods call to Debugger trait object inside the supplied EngineState.
+#[derive(Clone, Copy, Debug)]
+pub struct WithDebug;
+
+impl DebugContext for WithDebug {
+    fn enter_block(engine_state: &EngineState, block: &Block) {
+        if let Ok(mut debugger) = engine_state.debugger.lock() {
+            debugger.deref_mut().enter_block(engine_state, block);
+        }
+    }
+
+    fn leave_block(engine_state: &EngineState, block: &Block) {
+        if let Ok(mut debugger) = engine_state.debugger.lock() {
+            debugger.deref_mut().leave_block(engine_state, block);
+        }
+    }
+
+    fn enter_element(engine_state: &EngineState, element: &PipelineElement) {
+        if let Ok(mut debugger) = engine_state.debugger.lock() {
+            debugger.deref_mut().enter_element(engine_state, element);
+        }
+    }
+
+    fn leave_element(
+        engine_state: &EngineState,
+        element: &PipelineElement,
+        result: &Result<(PipelineData, bool), ShellError>,
+    ) {
+        if let Ok(mut debugger) = engine_state.debugger.lock() {
+            debugger
+                .deref_mut()
+                .leave_element(engine_state, element, result);
+        }
+    }
+}
+
+/// Marker struct signalizing that evaluation should NOT use a Debugger
+///
+/// Trait methods are empty calls to be optimized away.
+#[derive(Clone, Copy, Debug)]
+pub struct WithoutDebug;
+
+impl DebugContext for WithoutDebug {}
+
+/// Debugger trait that every debugger needs to implement.
+///
+/// By default, its methods are empty. Not every Debugger needs to implement all of them.
+pub trait Debugger: Send + Debug {
+    /// Called by EngineState::activate_debugger().
+    ///
+    /// Intended for initializing the debugger.
+    fn activate(&mut self) {}
+
+    /// Called by EngineState::deactivate_debugger().
+    ///
+    /// Intended for wrapping up the debugger after a debugging session before returning back to
+    /// normal evaluation without debugging.
+    fn deactivate(&mut self) {}
+
+    /// Called when the evaluator enters a block
+    #[allow(unused_variables)]
+    fn enter_block(&mut self, engine_state: &EngineState, block: &Block) {}
+
+    /// Called when the evaluator leaves a block
+    #[allow(unused_variables)]
+    fn leave_block(&mut self, engine_state: &EngineState, block: &Block) {}
+
+    /// Called when the evaluator enters a pipeline element
+    #[allow(unused_variables)]
+    fn enter_element(&mut self, engine_state: &EngineState, pipeline_element: &PipelineElement) {}
+
+    /// Called when the evaluator leaves a pipeline element
+    #[allow(unused_variables)]
+    fn leave_element(
+        &mut self,
+        engine_state: &EngineState,
+        element: &PipelineElement,
+        result: &Result<(PipelineData, bool), ShellError>,
+    ) {
+    }
+
+    /// Create a final report as a Value
+    ///
+    /// Intended to be called after deactivate()
+    #[allow(unused_variables)]
+    fn report(&self, engine_state: &EngineState, debugger_span: Span) -> Result<Value, ShellError> {
+        Ok(Value::nothing(debugger_span))
+    }
+}
+
+/// A debugger that does nothing
+///
+/// Used as a placeholder debugger when not debugging.
+#[derive(Debug)]
+pub struct NoopDebugger;
+
+impl Debugger for NoopDebugger {}

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

@@ -0,0 +1,5 @@
+pub mod debugger_trait;
+pub mod profiler;
+
+pub use debugger_trait::*;
+pub use profiler::*;

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

@@ -0,0 +1,360 @@
+//! Nushell Profiler
+//!
+//! Profiler implements the Debugger trait and can be used via the `debug profile` command for
+//! profiling Nushell code.
+
+use crate::ast::{Block, Expr, PipelineElement};
+use crate::debugger::Debugger;
+use crate::engine::EngineState;
+use crate::record;
+use crate::{PipelineData, ShellError, Span, Value};
+use std::time::Instant;
+
+#[derive(Debug, Clone, Copy)]
+struct ElementId(usize);
+
+/// Stores profiling information about one pipeline element
+#[derive(Debug, Clone)]
+struct ElementInfo {
+    start: Instant,
+    duration_sec: f64,
+    depth: i64,
+    element_span: Span,
+    element_output: Option<Value>,
+    expr: Option<String>,
+    children: Vec<ElementId>,
+}
+
+impl ElementInfo {
+    pub fn new(depth: i64, element_span: Span) -> Self {
+        ElementInfo {
+            start: Instant::now(),
+            duration_sec: 0.0,
+            depth,
+            element_span,
+            element_output: None,
+            expr: None,
+            children: vec![],
+        }
+    }
+}
+
+/// Basic profiler, used in `debug profile`
+#[derive(Debug, Clone)]
+pub struct Profiler {
+    depth: i64,
+    max_depth: i64,
+    collect_spans: bool,
+    collect_source: bool,
+    collect_expanded_source: bool,
+    collect_values: bool,
+    collect_exprs: bool,
+    elements: Vec<ElementInfo>,
+    element_stack: Vec<ElementId>,
+}
+
+impl Profiler {
+    pub fn new(
+        max_depth: i64,
+        collect_spans: bool,
+        collect_source: bool,
+        collect_expanded_source: bool,
+        collect_values: bool,
+        collect_exprs: bool,
+        span: Span,
+    ) -> Self {
+        let first = ElementInfo {
+            start: Instant::now(),
+            duration_sec: 0.0,
+            depth: 0,
+            element_span: span,
+            element_output: if collect_values {
+                Some(Value::nothing(span))
+            } else {
+                None
+            },
+            expr: if collect_exprs {
+                Some("call".to_string())
+            } else {
+                None
+            },
+            children: vec![],
+        };
+
+        Profiler {
+            depth: 0,
+            max_depth,
+            collect_spans,
+            collect_source,
+            collect_expanded_source,
+            collect_values,
+            collect_exprs,
+            elements: vec![first],
+            element_stack: vec![ElementId(0)],
+        }
+    }
+
+    fn last_element_id(&self) -> Option<ElementId> {
+        self.element_stack.last().copied()
+    }
+
+    fn last_element_mut(&mut self) -> Option<&mut ElementInfo> {
+        self.last_element_id()
+            .and_then(|id| self.elements.get_mut(id.0))
+    }
+}
+
+impl Debugger for Profiler {
+    fn activate(&mut self) {
+        let Some(root_element) = self.last_element_mut() else {
+            eprintln!("Profiler Error: Missing root element.");
+            return;
+        };
+
+        root_element.start = Instant::now();
+    }
+
+    fn deactivate(&mut self) {
+        let Some(root_element) = self.last_element_mut() else {
+            eprintln!("Profiler Error: Missing root element.");
+            return;
+        };
+
+        root_element.duration_sec = root_element.start.elapsed().as_secs_f64();
+    }
+
+    fn enter_block(&mut self, _engine_state: &EngineState, _block: &Block) {
+        self.depth += 1;
+    }
+
+    fn leave_block(&mut self, _engine_state: &EngineState, _block: &Block) {
+        self.depth -= 1;
+    }
+
+    fn enter_element(&mut self, engine_state: &EngineState, element: &PipelineElement) {
+        if self.depth > self.max_depth {
+            return;
+        }
+
+        let Some(parent_id) = self.last_element_id() else {
+            eprintln!("Profiler Error: Missing parent element ID.");
+            return;
+        };
+
+        let expr_opt = if self.collect_exprs {
+            Some(match element {
+                PipelineElement::Expression(_, expression) => {
+                    expr_to_string(engine_state, &expression.expr)
+                }
+                _ => "other".to_string(),
+            })
+        } else {
+            None
+        };
+
+        let new_id = ElementId(self.elements.len());
+
+        let mut new_element = ElementInfo::new(self.depth, element.span());
+        new_element.expr = expr_opt;
+
+        self.elements.push(new_element);
+
+        let Some(parent) = self.elements.get_mut(parent_id.0) else {
+            eprintln!("Profiler Error: Missing parent element.");
+            return;
+        };
+
+        parent.children.push(new_id);
+        self.element_stack.push(new_id);
+    }
+
+    fn leave_element(
+        &mut self,
+        _engine_state: &EngineState,
+        element: &PipelineElement,
+        result: &Result<(PipelineData, bool), ShellError>,
+    ) {
+        if self.depth > self.max_depth {
+            return;
+        }
+
+        let element_span = element.span();
+
+        let out_opt = if self.collect_values {
+            Some(match result {
+                Ok((pipeline_data, _not_sure_what_this_is)) => match pipeline_data {
+                    PipelineData::Value(val, ..) => val.clone(),
+                    PipelineData::ListStream(..) => Value::string("list stream", element_span),
+                    PipelineData::ExternalStream { .. } => {
+                        Value::string("external stream", element_span)
+                    }
+                    _ => Value::nothing(element_span),
+                },
+                Err(e) => Value::error(e.clone(), element_span),
+            })
+        } else {
+            None
+        };
+
+        let Some(last_element) = self.last_element_mut() else {
+            eprintln!("Profiler Error: Missing last element.");
+            return;
+        };
+
+        last_element.duration_sec = last_element.start.elapsed().as_secs_f64();
+        last_element.element_output = out_opt;
+
+        self.element_stack.pop();
+    }
+
+    fn report(&self, engine_state: &EngineState, profiler_span: Span) -> Result<Value, ShellError> {
+        Ok(Value::list(
+            collect_data(
+                engine_state,
+                self,
+                ElementId(0),
+                ElementId(0),
+                profiler_span,
+            )?,
+            profiler_span,
+        ))
+    }
+}
+
+fn profiler_error(msg: impl Into<String>, span: Span) -> ShellError {
+    ShellError::GenericError {
+        error: "Profiler Error".to_string(),
+        msg: msg.into(),
+        span: Some(span),
+        help: None,
+        inner: vec![],
+    }
+}
+
+fn expr_to_string(engine_state: &EngineState, expr: &Expr) -> String {
+    match expr {
+        Expr::Binary(_) => "binary".to_string(),
+        Expr::BinaryOp(_, _, _) => "binary operation".to_string(),
+        Expr::Block(_) => "block".to_string(),
+        Expr::Bool(_) => "bool".to_string(),
+        Expr::Call(call) => {
+            let decl = engine_state.get_decl(call.decl_id);
+            if decl.name() == "collect" && call.head == Span::new(0, 0) {
+                "call (implicit collect)"
+            } else {
+                "call"
+            }
+            .to_string()
+        }
+        Expr::CellPath(_) => "cell path".to_string(),
+        Expr::Closure(_) => "closure".to_string(),
+        Expr::DateTime(_) => "datetime".to_string(),
+        Expr::Directory(_, _) => "directory".to_string(),
+        Expr::ExternalCall(_, _, _) => "external call".to_string(),
+        Expr::Filepath(_, _) => "filepath".to_string(),
+        Expr::Float(_) => "float".to_string(),
+        Expr::FullCellPath(full_cell_path) => {
+            let head = expr_to_string(engine_state, &full_cell_path.head.expr);
+            format!("full cell path ({head})")
+        }
+        Expr::Garbage => "garbage".to_string(),
+        Expr::GlobPattern(_, _) => "glob pattern".to_string(),
+        Expr::ImportPattern(_) => "import pattern".to_string(),
+        Expr::Int(_) => "int".to_string(),
+        Expr::Keyword(_, _, _) => "keyword".to_string(),
+        Expr::List(_) => "list".to_string(),
+        Expr::MatchBlock(_) => "match block".to_string(),
+        Expr::Nothing => "nothing".to_string(),
+        Expr::Operator(_) => "operator".to_string(),
+        Expr::Overlay(_) => "overlay".to_string(),
+        Expr::Range(_, _, _, _) => "range".to_string(),
+        Expr::Record(_) => "record".to_string(),
+        Expr::RowCondition(_) => "row condition".to_string(),
+        Expr::Signature(_) => "signature".to_string(),
+        Expr::Spread(_) => "spread".to_string(),
+        Expr::String(_) => "string".to_string(),
+        Expr::StringInterpolation(_) => "string interpolation".to_string(),
+        Expr::Subexpression(_) => "subexpression".to_string(),
+        Expr::Table(_, _) => "table".to_string(),
+        Expr::UnaryNot(_) => "unary not".to_string(),
+        Expr::ValueWithUnit(_, _) => "value with unit".to_string(),
+        Expr::Var(_) => "var".to_string(),
+        Expr::VarDecl(_) => "var decl".to_string(),
+    }
+}
+
+fn collect_data(
+    engine_state: &EngineState,
+    profiler: &Profiler,
+    element_id: ElementId,
+    parent_id: ElementId,
+    profiler_span: Span,
+) -> Result<Vec<Value>, ShellError> {
+    let element = &profiler.elements[element_id.0];
+
+    let mut row = record! {
+        "depth" => Value::int(element.depth, profiler_span),
+        "id" => Value::int(element_id.0 as i64, profiler_span),
+        "parent_id" => Value::int(parent_id.0 as i64, profiler_span),
+    };
+
+    if profiler.collect_spans {
+        let span_start = i64::try_from(element.element_span.start)
+            .map_err(|_| profiler_error("error converting span start to i64", profiler_span))?;
+        let span_end = i64::try_from(element.element_span.end)
+            .map_err(|_| profiler_error("error converting span end to i64", profiler_span))?;
+
+        row.push(
+            "span",
+            Value::record(
+                record! {
+                    "start" => Value::int(span_start, profiler_span),
+                    "end" => Value::int(span_end, profiler_span),
+                },
+                profiler_span,
+            ),
+        );
+    }
+
+    if profiler.collect_source {
+        let val = String::from_utf8_lossy(engine_state.get_span_contents(element.element_span));
+        let val = val.trim();
+        let nlines = val.lines().count();
+
+        let fragment = if profiler.collect_expanded_source {
+            val.to_string()
+        } else {
+            let mut first_line = val.lines().next().unwrap_or("").to_string();
+
+            if nlines > 1 {
+                first_line.push_str(" ...");
+            }
+
+            first_line
+        };
+
+        row.push("source", Value::string(fragment, profiler_span));
+    }
+
+    if let Some(expr_string) = &element.expr {
+        row.push("expr", Value::string(expr_string.clone(), profiler_span));
+    }
+
+    if let Some(val) = &element.element_output {
+        row.push("output", val.clone());
+    }
+
+    row.push(
+        "duration_ms",
+        Value::float(element.duration_sec * 1e3, profiler_span),
+    );
+
+    let mut rows = vec![Value::record(row, profiler_span)];
+
+    for child in &element.children {
+        let child_rows = collect_data(engine_state, profiler, *child, element_id, profiler_span)?;
+        rows.extend(child_rows);
+    }
+
+    Ok(rows)
+}

crates/nu-protocol/src/engine/engine_state.rs

@@ -4,6 +4,7 @@ use lru::LruCache;
 use super::{usage::build_usage, usage::Usage, StateDelta};
 use super::{Command, EnvVars, OverlayFrame, ScopeFrame, Stack, Visibility, DEFAULT_OVERLAY_NAME};
 use crate::ast::Block;
+use crate::debugger::{Debugger, NoopDebugger};
 use crate::{
     BlockId, Config, DeclId, Example, FileId, HistoryConfig, Module, ModuleId, OverlayId,
     ShellError, Signature, Span, Type, VarId, Variable, VirtualPathId,
@@ -14,11 +15,14 @@ use std::collections::HashMap;
 use std::num::NonZeroUsize;
 use std::path::Path;
 use std::path::PathBuf;
+use std::sync::atomic::Ordering;
 use std::sync::{
     atomic::{AtomicBool, AtomicU32},
-    Arc, Mutex,
+    Arc, Mutex, MutexGuard, PoisonError,
 };
 
+type PoisonDebuggerError<'a> = PoisonError<MutexGuard<'a, Box<dyn Debugger>>>;
+
 pub static PWD_ENV: &str = "PWD";
 
 #[derive(Clone, Debug)]
@@ -33,6 +37,20 @@ pub struct ReplState {
     pub cursor_pos: usize,
 }
 
+pub struct IsDebugging(AtomicBool);
+
+impl IsDebugging {
+    pub fn new(val: bool) -> Self {
+        IsDebugging(AtomicBool::new(val))
+    }
+}
+
+impl Clone for IsDebugging {
+    fn clone(&self) -> Self {
+        IsDebugging(AtomicBool::new(self.0.load(Ordering::Relaxed)))
+    }
+}
+
 /// The core global engine state. This includes all global definitions as well as any global state that
 /// will persist for the whole session.
 ///
@@ -104,6 +122,8 @@ pub struct EngineState {
     pub is_interactive: bool,
     pub is_login: bool,
     startup_time: i64,
+    is_debugging: IsDebugging,
+    pub debugger: Arc<Mutex<Box<dyn Debugger>>>,
 }
 
 // The max number of compiled regexes to keep around in a LRU cache, arbitrarily chosen
@@ -161,6 +181,8 @@ impl EngineState {
             is_interactive: false,
             is_login: false,
             startup_time: -1,
+            is_debugging: IsDebugging::new(false),
+            debugger: Arc::new(Mutex::new(Box::new(NoopDebugger))),
         }
     }
 
@@ -916,6 +938,29 @@ impl EngineState {
         self.startup_time = startup_time;
     }
 
+    pub fn activate_debugger(
+        &self,
+        debugger: Box<dyn Debugger>,
+    ) -> Result<(), PoisonDebuggerError> {
+        let mut locked_debugger = self.debugger.lock()?;
+        *locked_debugger = debugger;
+        locked_debugger.activate();
+        self.is_debugging.0.store(true, Ordering::Relaxed);
+        Ok(())
+    }
+
+    pub fn deactivate_debugger(&self) -> Result<Box<dyn Debugger>, PoisonDebuggerError> {
+        let mut locked_debugger = self.debugger.lock()?;
+        locked_debugger.deactivate();
+        let ret = std::mem::replace(&mut *locked_debugger, Box::new(NoopDebugger));
+        self.is_debugging.0.store(false, Ordering::Relaxed);
+        Ok(ret)
+    }
+
+    pub fn is_debugging(&self) -> bool {
+        self.is_debugging.0.load(Ordering::Relaxed)
+    }
+
     pub fn recover_from_panic(&mut self) {
         if Mutex::is_poisoned(&self.repl_state) {
             self.repl_state = Arc::new(Mutex::new(ReplState {

crates/nu-protocol/src/eval_base.rs

@@ -1,3 +1,4 @@
+use crate::debugger::DebugContext;
 use crate::{
     ast::{
         eval_operator, Assignment, Bits, Boolean, Call, Comparison, Expr, Expression,
@@ -5,6 +6,7 @@ use crate::{
     },
     Config, IntoInterruptiblePipelineData, Range, Record, ShellError, Span, Value, VarId,
 };
+
 use std::{borrow::Cow, collections::HashMap};
 
 /// To share implementations for regular eval and const eval
@@ -17,7 +19,7 @@ pub trait Eval {
     /// This is the stack for regular eval, and unused by const eval
     type MutState;
 
-    fn eval(
+    fn eval<D: DebugContext>(
         state: Self::State<'_>,
         mut_state: &mut Self::MutState,
         expr: &Expression,
@@ -34,7 +36,7 @@ pub trait Eval {
             Expr::Var(var_id) => Self::eval_var(state, mut_state, *var_id, expr.span),
             Expr::CellPath(cell_path) => Ok(Value::cell_path(cell_path.clone(), expr.span)),
             Expr::FullCellPath(cell_path) => {
-                let value = Self::eval(state, mut_state, &cell_path.head)?;
+                let value = Self::eval::<D>(state, mut_state, &cell_path.head)?;
 
                 value.follow_cell_path(&cell_path.tail, false)
             }
@@ -43,11 +45,11 @@ pub trait Eval {
                 let mut output = vec![];
                 for expr in x {
                     match &expr.expr {
-                        Expr::Spread(expr) => match Self::eval(state, mut_state, expr)? {
+                        Expr::Spread(expr) => match Self::eval::<D>(state, mut_state, expr)? {
                             Value::List { mut vals, .. } => output.append(&mut vals),
                             _ => return Err(ShellError::CannotSpreadAsList { span: expr.span }),
                         },
-                        _ => output.push(Self::eval(state, mut_state, expr)?),
+                        _ => output.push(Self::eval::<D>(state, mut_state, expr)?),
                     }
                 }
                 Ok(Value::list(output, expr.span))
@@ -59,7 +61,7 @@ pub trait Eval {
                     match item {
                         RecordItem::Pair(col, val) => {
                             // avoid duplicate cols
-                            let col_name = Self::eval(state, mut_state, col)?.coerce_into_string()?;
+                            let col_name = Self::eval::<D>(state, mut_state, col)?.coerce_into_string()?;
                             if let Some(orig_span) = col_names.get(&col_name) {
                                 return Err(ShellError::ColumnDefinedTwice {
                                     col_name,
@@ -68,11 +70,11 @@ pub trait Eval {
                                 });
                             } else {
                                 col_names.insert(col_name.clone(), col.span);
-                                record.push(col_name, Self::eval(state, mut_state, val)?);
+                                record.push(col_name, Self::eval::<D>(state, mut_state, val)?);
                             }
                         }
                         RecordItem::Spread(_, inner) => {
-                            match Self::eval(state, mut_state, inner)? {
+                            match Self::eval::<D>(state, mut_state, inner)? {
                                 Value::Record { val: inner_val, .. } => {
                                     for (col_name, val) in inner_val {
                                         if let Some(orig_span) = col_names.get(&col_name) {
@@ -102,7 +104,7 @@ pub trait Eval {
             Expr::Table(headers, vals) => {
                 let mut output_headers = vec![];
                 for expr in headers {
-                    let header = Self::eval(state, mut_state, expr)?.coerce_into_string()?;
+                    let header = Self::eval::<D>(state, mut_state, expr)?.coerce_into_string()?;
                     if let Some(idx) = output_headers
                         .iter()
                         .position(|existing| existing == &header)
@@ -120,7 +122,7 @@ pub trait Eval {
                 let mut output_rows = vec![];
                 for val in vals {
                     let record = output_headers.iter().zip(val).map(|(col, expr)| {
-                        Self::eval(state, mut_state, expr).map(|val| (col.clone(), val))
+                        Self::eval::<D>(state, mut_state, expr).map(|val| (col.clone(), val))
                     }).collect::<Result<_,_>>()?;
 
                     output_rows.push(Value::record(
@@ -130,10 +132,10 @@ pub trait Eval {
                 }
                 Ok(Value::list(output_rows, expr.span))
             }
-            Expr::Keyword(_, _, expr) => Self::eval(state, mut_state, expr),
+            Expr::Keyword(_, _, expr) => Self::eval::<D>(state, mut_state, expr),
             Expr::String(s) => Ok(Value::string(s.clone(), expr.span)),
             Expr::Nothing => Ok(Value::nothing(expr.span)),
-            Expr::ValueWithUnit(e, unit) => match Self::eval(state, mut_state, e)? {
+            Expr::ValueWithUnit(e, unit) => match Self::eval::<D>(state, mut_state, e)? {
                 Value::Int { val, .. } => unit.item.to_value(val, unit.span),
                 x => Err(ShellError::CantConvert {
                     to_type: "unit value".into(),
@@ -142,28 +144,28 @@ pub trait Eval {
                     help: None,
                 }),
             },
-            Expr::Call(call) => Self::eval_call(state, mut_state, call, expr.span),
+            Expr::Call(call) => Self::eval_call::<D>(state, mut_state, call, expr.span),
             Expr::ExternalCall(head, args, is_subexpression) => {
                 Self::eval_external_call(state, mut_state, head, args, *is_subexpression, expr.span)
             }
             Expr::Subexpression(block_id) => {
-                Self::eval_subexpression(state, mut_state, *block_id, expr.span)
+                Self::eval_subexpression::<D>(state, mut_state, *block_id, expr.span)
             }
             Expr::Range(from, next, to, operator) => {
                 let from = if let Some(f) = from {
-                    Self::eval(state, mut_state, f)?
+                    Self::eval::<D>(state, mut_state, f)?
                 } else {
                     Value::nothing(expr.span)
                 };
 
                 let next = if let Some(s) = next {
-                    Self::eval(state, mut_state, s)?
+                    Self::eval::<D>(state, mut_state, s)?
                 } else {
                     Value::nothing(expr.span)
                 };
 
                 let to = if let Some(t) = to {
-                    Self::eval(state, mut_state, t)?
+                    Self::eval::<D>(state, mut_state, t)?
                 } else {
                     Value::nothing(expr.span)
                 };
@@ -173,7 +175,7 @@ pub trait Eval {
                 ))
             }
             Expr::UnaryNot(expr) => {
-                let lhs = Self::eval(state, mut_state, expr)?;
+                let lhs = Self::eval::<D>(state, mut_state, expr)?;
                 match lhs {
                     Value::Bool { val, .. } => Ok(Value::bool(!val, expr.span)),
                     other => Err(ShellError::TypeMismatch {
@@ -188,13 +190,13 @@ pub trait Eval {
 
                 match op {
                     Operator::Boolean(boolean) => {
-                        let lhs = Self::eval(state, mut_state, lhs)?;
+                        let lhs = Self::eval::<D>(state, mut_state, lhs)?;
                         match boolean {
                             Boolean::And => {
                                 if lhs.is_false() {
                                     Ok(Value::bool(false, expr.span))
                                 } else {
-                                    let rhs = Self::eval(state, mut_state, rhs)?;
+                                    let rhs = Self::eval::<D>(state, mut_state, rhs)?;
                                     lhs.and(op_span, &rhs, expr.span)
                                 }
                             }
@@ -202,19 +204,19 @@ pub trait Eval {
                                 if lhs.is_true() {
                                     Ok(Value::bool(true, expr.span))
                                 } else {
-                                    let rhs = Self::eval(state, mut_state, rhs)?;
+                                    let rhs = Self::eval::<D>(state, mut_state, rhs)?;
                                     lhs.or(op_span, &rhs, expr.span)
                                 }
                             }
                             Boolean::Xor => {
-                                let rhs = Self::eval(state, mut_state, rhs)?;
+                                let rhs = Self::eval::<D>(state, mut_state, rhs)?;
                                 lhs.xor(op_span, &rhs, expr.span)
                             }
                         }
                     }
                     Operator::Math(math) => {
-                        let lhs = Self::eval(state, mut_state, lhs)?;
-                        let rhs = Self::eval(state, mut_state, rhs)?;
+                        let lhs = Self::eval::<D>(state, mut_state, lhs)?;
+                        let rhs = Self::eval::<D>(state, mut_state, rhs)?;
 
                         match math {
                             Math::Plus => lhs.add(op_span, &rhs, expr.span),
@@ -228,8 +230,8 @@ pub trait Eval {
                         }
                     }
                     Operator::Comparison(comparison) => {
-                        let lhs = Self::eval(state, mut_state, lhs)?;
-                        let rhs = Self::eval(state, mut_state, rhs)?;
+                        let lhs = Self::eval::<D>(state, mut_state, lhs)?;
+                        let rhs = Self::eval::<D>(state, mut_state, rhs)?;
                         match comparison {
                             Comparison::LessThan => lhs.lt(op_span, &rhs, expr.span),
                             Comparison::LessThanOrEqual => lhs.lte(op_span, &rhs, expr.span),
@@ -250,8 +252,8 @@ pub trait Eval {
                         }
                     }
                     Operator::Bits(bits) => {
-                        let lhs = Self::eval(state, mut_state, lhs)?;
-                        let rhs = Self::eval(state, mut_state, rhs)?;
+                        let lhs = Self::eval::<D>(state, mut_state, lhs)?;
+                        let rhs = Self::eval::<D>(state, mut_state, rhs)?;
                         match bits {
                             Bits::BitAnd => lhs.bit_and(op_span, &rhs, expr.span),
                             Bits::BitOr => lhs.bit_or(op_span, &rhs, expr.span),
@@ -260,8 +262,8 @@ pub trait Eval {
                             Bits::ShiftRight => lhs.bit_shr(op_span, &rhs, expr.span),
                         }
                     }
-                    Operator::Assignment(assignment) => Self::eval_assignment(
-                        state, mut_state, lhs, rhs, assignment, op_span, expr.span,
+                    Operator::Assignment(assignment) => Self::eval_assignment::<D>(
+                        state, mut_state, lhs, rhs, assignment, op_span, expr.span
                     ),
                 }
             }
@@ -272,7 +274,7 @@ pub trait Eval {
             Expr::StringInterpolation(exprs) => {
                 let mut parts = vec![];
                 for expr in exprs {
-                    parts.push(Self::eval(state, mut_state, expr)?);
+                    parts.push(Self::eval::<D>(state, mut_state, expr)?);
                 }
 
                 let config = Self::get_config(state, mut_state);
@@ -324,7 +326,7 @@ pub trait Eval {
         span: Span,
     ) -> Result<Value, ShellError>;
 
-    fn eval_call(
+    fn eval_call<D: DebugContext>(
         state: Self::State<'_>,
         mut_state: &mut Self::MutState,
         call: &Call,
@@ -340,7 +342,7 @@ pub trait Eval {
         span: Span,
     ) -> Result<Value, ShellError>;
 
-    fn eval_subexpression(
+    fn eval_subexpression<D: DebugContext>(
         state: Self::State<'_>,
         mut_state: &mut Self::MutState,
         block_id: usize,
@@ -356,7 +358,8 @@ pub trait Eval {
         expr_span: Span,
     ) -> Result<Value, ShellError>;
 
-    fn eval_assignment(
+    #[allow(clippy::too_many_arguments)]
+    fn eval_assignment<D: DebugContext>(
         state: Self::State<'_>,
         mut_state: &mut Self::MutState,
         lhs: &Expression,

crates/nu-protocol/src/eval_const.rs

@@ -1,3 +1,4 @@
+use crate::debugger::{DebugContext, WithoutDebug};
 use crate::{
     ast::{Assignment, Block, Call, Expr, Expression, ExternalArgument, PipelineElement},
     engine::{EngineState, StateWorkingSet},
@@ -5,10 +6,8 @@ use crate::{
     record, Config, HistoryFileFormat, PipelineData, Record, ShellError, Span, Value, VarId,
 };
 use nu_system::os_info::{get_kernel_version, get_os_arch, get_os_family, get_os_name};
-use std::{
-    borrow::Cow,
-    path::{Path, PathBuf},
-};
+use std::borrow::Cow;
+use std::path::{Path, PathBuf};
 
 pub fn create_nu_constant(engine_state: &EngineState, span: Span) -> Result<Value, ShellError> {
     fn canonicalize_path(engine_state: &EngineState, path: &Path) -> PathBuf {
@@ -257,7 +256,8 @@ pub fn eval_constant(
     working_set: &StateWorkingSet,
     expr: &Expression,
 ) -> Result<Value, ShellError> {
-    <EvalConst as Eval>::eval(working_set, &mut (), expr)
+    // TODO: Allow debugging const eval
+    <EvalConst as Eval>::eval::<WithoutDebug>(working_set, &mut (), expr)
 }
 
 struct EvalConst;
@@ -303,12 +303,13 @@ impl Eval for EvalConst {
         }
     }
 
-    fn eval_call(
+    fn eval_call<D: DebugContext>(
         working_set: &StateWorkingSet,
         _: &mut (),
         call: &Call,
         span: Span,
     ) -> Result<Value, ShellError> {
+        // TODO: Allow debugging const eval
         // TODO: eval.rs uses call.head for the span rather than expr.span
         Ok(eval_const_call(working_set, call, PipelineData::empty())?.into_value(span))
     }
@@ -325,12 +326,13 @@ impl Eval for EvalConst {
         Err(ShellError::NotAConstant { span })
     }
 
-    fn eval_subexpression(
+    fn eval_subexpression<D: DebugContext>(
         working_set: &StateWorkingSet,
         _: &mut (),
         block_id: usize,
         span: Span,
     ) -> Result<Value, ShellError> {
+        // TODO: Allow debugging const eval
         let block = working_set.get_block(block_id);
         Ok(
             eval_const_subexpression(working_set, block, PipelineData::empty(), span)?
@@ -349,7 +351,7 @@ impl Eval for EvalConst {
         Err(ShellError::NotAConstant { span: expr_span })
     }
 
-    fn eval_assignment(
+    fn eval_assignment<D: DebugContext>(
         _: &StateWorkingSet,
         _: &mut (),
         _: &Expression,
@@ -358,6 +360,7 @@ impl Eval for EvalConst {
         _op_span: Span,
         expr_span: Span,
     ) -> Result<Value, ShellError> {
+        // TODO: Allow debugging const eval
         Err(ShellError::NotAConstant { span: expr_span })
     }
 

crates/nu-protocol/src/lib.rs

@@ -2,6 +2,7 @@ mod alias;
 pub mod ast;
 pub mod cli_error;
 pub mod config;
+pub mod debugger;
 mod did_you_mean;
 pub mod engine;
 pub mod eval_base;

crates/nu-std/src/lib.rs

@@ -2,6 +2,7 @@ use std::path::PathBuf;
 
 use nu_engine::{env::current_dir, eval_block};
 use nu_parser::parse;
+use nu_protocol::debugger::WithoutDebug;
 use nu_protocol::engine::{Stack, StateWorkingSet, VirtualPath};
 use nu_protocol::{report_error, PipelineData};
 
@@ -92,7 +93,8 @@ use std pwd
     // We need to evaluate the module in order to run the `export-env` blocks.
     let mut stack = Stack::new();
     let pipeline_data = PipelineData::Empty;
-    eval_block(
+
+    eval_block::<WithoutDebug>(
         engine_state,
         &mut stack,
         &block,

src/test_bins.rs

@@ -1,6 +1,7 @@
 use nu_cmd_base::hook::{eval_env_change_hook, eval_hook};
 use nu_engine::eval_block;
 use nu_parser::parse;
+use nu_protocol::debugger::WithoutDebug;
 use nu_protocol::engine::{EngineState, Stack, StateWorkingSet};
 use nu_protocol::{CliError, PipelineData, Value};
 use nu_std::load_standard_library;
@@ -320,7 +321,7 @@ pub fn nu_repl() {
         let input = PipelineData::empty();
         let config = engine_state.get_config();
 
-        match eval_block(&engine_state, &mut stack, &block, input, false, false) {
+        match eval_block::<WithoutDebug>(&engine_state, &mut stack, &block, input, false, false) {
             Ok(pipeline_data) => match pipeline_data.collect_string("", config) {
                 Ok(s) => last_output = s,
                 Err(err) => outcome_err(&engine_state, &err),