preserve variable capture spans in blocks (#15334)

Closes #15160

# User-Facing Changes

Certain "variable not found" errors no longer highlight the surrounding
block.

Before:

```nushell
do {
  match foo {
    _ => $in
  }
}

Error: nu:🐚:variable_not_found

  × Variable not found
   ╭─[entry #1:1:1]
 1 │ ╭─▶ do {
 2 │ │     match foo {
 3 │ │       _ => $in
 4 │ │     }
 5 │ ├─▶ }
   · ╰──── variable not found
```

After:

```nushell
Error: nu:🐚:variable_not_found

  × Variable not found
   ╭─[entry #1:3:10]
 2 │   match foo {
 3 │     _ => $in
   ·          ─┬─
   ·           ╰── variable not found
```

crates/nu-engine/src/eval.rs

@@ -642,17 +642,17 @@ impl Eval for EvalRuntime {
             .get_block(block_id)
             .captures
             .iter()
-            .map(|&id| {
+            .map(|(id, span)| {
                 stack
-                    .get_var(id, span)
+                    .get_var(*id, *span)
                     .or_else(|_| {
                         engine_state
-                            .get_var(id)
+                            .get_var(*id)
                             .const_val
                             .clone()
-                            .ok_or(ShellError::VariableNotFoundAtRuntime { span })
+                            .ok_or(ShellError::VariableNotFoundAtRuntime { span: *span })
                     })
-                    .map(|var| (id, var))
+                    .map(|var| (*id, var))
             })
             .collect::<Result<_, _>>()?;
 

crates/nu-engine/src/eval_ir.rs

@@ -857,7 +857,7 @@ fn literal_value(
             let captures = block
                 .captures
                 .iter()
-                .map(|var_id| get_var(ctx, *var_id, span).map(|val| (*var_id, val)))
+                .map(|(var_id, span)| get_var(ctx, *var_id, *span).map(|val| (*var_id, val)))
                 .collect::<Result<Vec<_>, ShellError>>()?;
             Value::closure(
                 Closure {

crates/nu-parser/src/parser.rs

@@ -6589,9 +6589,9 @@ pub fn discover_captures_in_expr(
                     None => {
                         let block = working_set.get_block(block_id);
                         if !block.captures.is_empty() {
-                            for capture in &block.captures {
+                            for (capture, span) in &block.captures {
                                 if !seen.contains(capture) {
-                                    output.push((*capture, call.head));
+                                    output.push((*capture, *span));
                                 }
                             }
                         } else {
@@ -6905,8 +6905,7 @@ pub fn parse(
         &mut captures,
     ) {
         Ok(_) => {
-            Arc::make_mut(&mut output).captures =
+            Arc::make_mut(&mut output).captures = captures;
-                captures.into_iter().map(|(var_id, _)| var_id).collect();
         }
         Err(err) => working_set.error(err),
     }
@@ -6961,7 +6960,7 @@ pub fn parse(
             && block_id.get() >= working_set.permanent_state.num_blocks()
         {
             let block = working_set.get_block_mut(block_id);
-            block.captures = captures.into_iter().map(|(var_id, _)| var_id).collect();
+            block.captures = captures;
         }
     }
 

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

@@ -6,7 +6,7 @@ use serde::{Deserialize, Serialize};
 pub struct Block {
     pub signature: Box<Signature>,
     pub pipelines: Vec<Pipeline>,
-    pub captures: Vec<VarId>,
+    pub captures: Vec<(VarId, Span)>,
     pub redirect_env: bool,
     /// The block compiled to IR instructions. Not available for subexpressions.
     pub ir_block: Option<IrBlock>,

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

@@ -111,7 +111,10 @@ impl Expression {
             Expr::UnaryNot(expr) => expr.has_in_variable(working_set),
             Expr::Block(block_id) | Expr::Closure(block_id) => {
                 let block = working_set.get_block(*block_id);
-                block.captures.contains(&IN_VARIABLE_ID)
+                block
+                    .captures
+                    .iter()
+                    .any(|(var_id, _)| var_id == &IN_VARIABLE_ID)
                     || block
                         .pipelines
                         .iter()

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

@@ -322,12 +322,12 @@ impl Stack {
         }
     }
 
-    pub fn gather_captures(&self, engine_state: &EngineState, captures: &[VarId]) -> Stack {
+    pub fn gather_captures(&self, engine_state: &EngineState, captures: &[(VarId, Span)]) -> Stack {
         let mut vars = Vec::with_capacity(captures.len());
 
         let fake_span = Span::new(0, 0);
 
-        for capture in captures {
+        for (capture, _) in captures {
             // Note: this assumes we have calculated captures correctly and that commands
             // that take in a var decl will manually set this into scope when running the blocks
             if let Ok(value) = self.get_var(*capture, fake_span) {