fix(es/compat): Consider only the variables used in the closure (#9151)

**Description:**

The original code separately records the usage of variables and checks if there is a closure. Changed to only record variables used in a closure.

**Related issue:**

 - Closes #8010

crates/swc/tests/fixture/issues-3xxx/3417/1/output/index.ts

@@ -6,36 +6,36 @@ export function selectRooms(building) {
     }
     var _iteratorNormalCompletion = true, _didIteratorError = false, _iteratorError = undefined;
     try {
-        var _loop = function() {
+        for(var _iterator = levels[Symbol.iterator](), _step; !(_iteratorNormalCompletion = (_step = _iterator.next()).done); _iteratorNormalCompletion = true){
             var level = _step.value;
             var levelId = level.id;
             var levelRooms = roomsOnLevel(levelId, rooms, roomsByLevel);
             var sortedRooms = [];
-            var _iteratorNormalCompletion = true, _didIteratorError = false, _iteratorError = undefined;
+            var _iteratorNormalCompletion1 = true, _didIteratorError1 = false, _iteratorError1 = undefined;
             try {
-                for(var _iterator = levelRooms[Symbol.iterator](), _step1; !(_iteratorNormalCompletion = (_step1 = _iterator.next()).done); _iteratorNormalCompletion = true){
+                for(var _iterator1 = levelRooms[Symbol.iterator](), _step1; !(_iteratorNormalCompletion1 = (_step1 = _iterator1.next()).done); _iteratorNormalCompletion1 = true){
                     var room = _step1.value;
                     sortedRooms.push(room);
                 }
             } catch (err) {
-                _didIteratorError = true;
-                _iteratorError = err;
+                _didIteratorError1 = true;
+                _iteratorError1 = err;
             } finally{
                 try {
-                    if (!_iteratorNormalCompletion && _iterator.return != null) {
-                        _iterator.return();
+                    if (!_iteratorNormalCompletion1 && _iterator1.return != null) {
+                        _iterator1.return();
                     }
                 } finally{
-                    if (_didIteratorError) {
-                        throw _iteratorError;
+                    if (_didIteratorError1) {
+                        throw _iteratorError1;
                     }
                 }
             }
             sortedRooms.sort(function(a, b) {
                 return a + b;
             });
             var visitedRooms = {};
-            var _iteratorNormalCompletion1 = true, _didIteratorError1 = false, _iteratorError1 = undefined;
+            var _iteratorNormalCompletion2 = true, _didIteratorError2 = false, _iteratorError2 = undefined;
             try {
                 var _loop = function() {
                     var room = _step2.value;
@@ -79,23 +79,22 @@ export function selectRooms(building) {
                         FLOOR_MAPPING[levelId]
                     ];
                 };
-                for(var _iterator1 = sortedRooms[Symbol.iterator](), _step2; !(_iteratorNormalCompletion1 = (_step2 = _iterator1.next()).done); _iteratorNormalCompletion1 = true)_loop();
+                for(var _iterator2 = sortedRooms[Symbol.iterator](), _step2; !(_iteratorNormalCompletion2 = (_step2 = _iterator2.next()).done); _iteratorNormalCompletion2 = true)_loop();
             } catch (err) {
-                _didIteratorError1 = true;
-                _iteratorError1 = err;
+                _didIteratorError2 = true;
+                _iteratorError2 = err;
             } finally{
                 try {
-                    if (!_iteratorNormalCompletion1 && _iterator1.return != null) {
-                        _iterator1.return();
+                    if (!_iteratorNormalCompletion2 && _iterator2.return != null) {
+                        _iterator2.return();
                     }
                 } finally{
-                    if (_didIteratorError1) {
-                        throw _iteratorError1;
+                    if (_didIteratorError2) {
+                        throw _iteratorError2;
                     }
                 }
             }
-        };
-        for(var _iterator = levels[Symbol.iterator](), _step; !(_iteratorNormalCompletion = (_step = _iterator.next()).done); _iteratorNormalCompletion = true)_loop();
+        }
     } catch (err) {
         _didIteratorError = true;
         _iteratorError = err;

crates/swc_ecma_compat_es2015/src/block_scoping/mod.rs

@@ -16,8 +16,7 @@ use swc_ecma_utils::{
     ExprFactory, StmtLike,
 };
 use swc_ecma_visit::{
-    as_folder, noop_visit_mut_type, noop_visit_type, visit_mut_obj_and_computed, Fold, Visit,
-    VisitMut, VisitMutWith, VisitWith,
+    as_folder, noop_visit_mut_type, visit_mut_obj_and_computed, Fold, VisitMut, VisitMutWith,
 };
 use swc_trace_macro::swc_trace;
 
@@ -100,17 +99,19 @@ impl BlockScoping {
     }
 
     fn mark_as_used(&mut self, i: Id) {
-        for (idx, scope) in self.scope.iter_mut().rev().enumerate() {
+        // Only consider the variable used in a non-ScopeKind::Loop, which means it is
+        // captured in a closure
+        for scope in self
+            .scope
+            .iter_mut()
+            .rev()
+            .skip_while(|scope| matches!(scope, ScopeKind::Loop { .. }))
+        {
             if let ScopeKind::Loop {
                 lexical_var, used, ..
             } = scope
             {
-                //
                 if lexical_var.contains(&i) {
-                    if idx == 0 {
-                        return;
-                    }
-
                     used.push(i);
                     return;
                 }
@@ -128,16 +129,6 @@ impl BlockScoping {
     fn handle_capture_of_vars(&mut self, body: &mut Box<Stmt>) {
         let body_stmt = &mut **body;
 
-        {
-            let mut v = FunctionFinder { found: false };
-            body_stmt.visit_with(&mut v);
-            if !v.found {
-                self.scope.pop();
-                return;
-            }
-        }
-
-        //
         if let Some(ScopeKind::Loop {
             args,
             used,
@@ -935,45 +926,3 @@ impl VisitMut for MutationHandler<'_> {
         n.arg = Some(Box::new(self.make_reassignment(val)))
     }
 }
-
-#[derive(Debug)]
-struct FunctionFinder {
-    found: bool,
-}
-
-impl Visit for FunctionFinder {
-    noop_visit_type!();
-
-    fn visit_arrow_expr(&mut self, _: &ArrowExpr) {
-        self.found = true;
-    }
-
-    /// Do not recurse into nested loop.
-    ///
-    /// https://github.com/swc-project/swc/issues/2622
-    fn visit_do_while_stmt(&mut self, _: &DoWhileStmt) {}
-
-    /// Do not recurse into nested loop.
-    ///
-    /// https://github.com/swc-project/swc/issues/2622
-    fn visit_for_in_stmt(&mut self, _: &ForInStmt) {}
-
-    /// Do not recurse into nested loop.
-    ///
-    /// https://github.com/swc-project/swc/issues/2622
-    fn visit_for_of_stmt(&mut self, _: &ForOfStmt) {}
-
-    /// Do not recurse into nested loop.
-    ///
-    /// https://github.com/swc-project/swc/issues/2622
-    fn visit_for_stmt(&mut self, _: &ForStmt) {}
-
-    fn visit_function(&mut self, _: &Function) {
-        self.found = true
-    }
-
-    /// Do not recurse into nested loop.
-    ///
-    /// https://github.com/swc-project/swc/issues/2622
-    fn visit_while_stmt(&mut self, _: &WhileStmt) {}
-}

crates/swc_ecma_transforms_compat/tests/for-of/issue-8010/1/exec.js

@@ -0,0 +1,5 @@
+for (const x of [0, 1, 2]) {
+    for (let i = 0; i < 1; i++) {
+        setTimeout(() => console.log(x));
+    }
+}