resolving external highlight should take current PATH into account (#11618)

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# Description

When resolving external commands, the current `PATH` was not taken into
account.

# User-Facing Changes
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helps us keep track of breaking changes. -->

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

@@ -28,7 +28,7 @@ impl Command for NuHighlight {
     fn run(
         &self,
         engine_state: &EngineState,
-        _stack: &mut Stack,
+        stack: &mut Stack,
         call: &Call,
         input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
@@ -40,6 +40,7 @@ impl Command for NuHighlight {
 
         let highlighter = crate::NuHighlighter {
             engine_state,
+            stack: std::sync::Arc::new(stack.clone()),
             config,
         };
 

crates/nu-cli/src/repl.rs

@@ -236,6 +236,7 @@ pub fn evaluate_repl(
             .use_bracketed_paste(cfg!(not(target_os = "windows")) && config.bracketed_paste)
             .with_highlighter(Box::new(NuHighlighter {
                 engine_state: engine_reference.clone(),
+                stack: std::sync::Arc::new(stack.clone()),
                 config: config.clone(),
             }))
             .with_validator(Box::new(NuValidator {

crates/nu-cli/src/syntax_highlight.rs

@@ -1,15 +1,17 @@
 use log::trace;
 use nu_ansi_term::Style;
 use nu_color_config::{get_matching_brackets_style, get_shape_color};
+use nu_engine::env;
 use nu_parser::{flatten_block, parse, FlatShape};
 use nu_protocol::ast::{Argument, Block, Expr, Expression, PipelineElement, RecordItem};
-use nu_protocol::engine::{EngineState, StateWorkingSet};
+use nu_protocol::engine::{EngineState, Stack, StateWorkingSet};
 use nu_protocol::{Config, Span};
 use reedline::{Highlighter, StyledText};
 use std::sync::Arc;
 
 pub struct NuHighlighter {
     pub engine_state: Arc<EngineState>,
+    pub stack: Arc<Stack>,
     pub config: Config,
 }
 
@@ -32,7 +34,17 @@ impl Highlighter for NuHighlighter {
                             working_set.get_span_contents(Span::new(span.start, span.end));
 
                         let str_word = String::from_utf8_lossy(str_contents).to_string();
-                        if which::which(str_word).ok().is_some() {
+                        let paths = env::path_str(&self.engine_state, &self.stack, *span).ok();
+                        let res = if let Ok(cwd) =
+                            env::current_dir_str(&self.engine_state, &self.stack)
+                        {
+                            which::which_in(str_word, paths.as_ref(), cwd).ok()
+                        } else {
+                            which::which_in_global(str_word, paths.as_ref())
+                                .ok()
+                                .and_then(|mut i| i.next())
+                        };
+                        if res.is_some() {
                             *shape = FlatShape::ExternalResolved;
                         }
                     }