Fix capture logic for inner closures (#9754)

# Description

This fixes the variable capture logic for closures in two cases:

* Closures inside of closures did not properly register the closures (or
lack thereof) in the outer closure
* Closures which called their inner closures before definition did not
properly calculate the closures of the outer closure

Example of the first case:
```
do { let b = 3; def c [] { $b }; c }
```

Example of the second case (notice `c` is called before it is defined):
```
do { let b = 3; c; def c [] { $b }; c }
```

# User-Facing Changes
This should strictly allow closures to work more correctly.

# Tests + Formatting
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crates/nu-parser/src/parser.rs

@@ -5894,25 +5894,44 @@ pub fn discover_captures_in_expr(
             if let Some(block_id) = decl.get_block_id() {
                 match seen_blocks.get(&block_id) {
                     Some(capture_list) => {
-                        output.extend(capture_list);
+                        // Push captures onto the outer closure that aren't created by that outer closure
+                        for capture in capture_list {
+                            if !seen.contains(&capture.0) {
+                                output.push(*capture);
+                            }
+                        }
                     }
                     None => {
                         let block = working_set.get_block(block_id);
                         if !block.captures.is_empty() {
-                            output.extend(block.captures.iter().map(|var_id| (*var_id, call.head)));
+                            for capture in &block.captures {
+                                if !seen.contains(capture) {
+                                    output.push((*capture, call.head));
+                                }
+                            }
                         } else {
-                            let mut seen = vec![];
-                            seen_blocks.insert(block_id, output.clone());
-
-                            let mut result = vec![];
-                            discover_captures_in_closure(
-                                working_set,
-                                block,
-                                &mut seen,
-                                seen_blocks,
-                                &mut result,
-                            )?;
-                            output.extend(&result);
+                            let result = {
+                                let mut seen = vec![];
+                                seen_blocks.insert(block_id, output.clone());
+
+                                let mut result = vec![];
+                                discover_captures_in_closure(
+                                    working_set,
+                                    block,
+                                    &mut seen,
+                                    seen_blocks,
+                                    &mut result,
+                                )?;
+
+                                result
+                            };
+                            // Push captures onto the outer closure that aren't created by that outer closure
+                            for capture in &result {
+                                if !seen.contains(&capture.0) {
+                                    output.push(*capture);
+                                }
+                            }
+
                             seen_blocks.insert(block_id, result);
                         }
                     }

src/tests/test_parser.rs

@@ -655,3 +655,13 @@ fn def_with_in_var_mut_2() -> TestResult {
         "3",
     )
 }
+
+#[test]
+fn properly_nest_captures() -> TestResult {
+    run_test(r#"do { let b = 3; def c [] { $b }; c }"#, "3")
+}
+
+#[test]
+fn properly_nest_captures_call_first() -> TestResult {
+    run_test(r#"do { let b = 3; c; def c [] { $b }; c }"#, "3")
+}