fix(es/utils): Fix detection of hoisting (#6738)

crates/swc_ecma_minifier/tests/terser/compress/dead_code/dead_code_2_should_warn/output.js

@@ -1,5 +1,5 @@
 function f() {
-    var x, g, q, y;
+    var x, g;
     g();
     x = 10;
     throw Error("foo");

crates/swc_ecma_minifier/tests/terser/compress/dead_code/dead_code_2_should_warn_strict/output.js

@@ -1,6 +1,6 @@
 "use strict";
 function f() {
-    var x, g, q, y;
+    var x, g;
     g();
     x = 10;
     throw Error("foo");

crates/swc_ecma_transforms_optimization/src/simplify/branch/tests.rs

@@ -1815,3 +1815,33 @@ fn issue_1825() {
 fn issue_1851_1() {
     test("x ?? (x = 'abc');", "x ?? (x = 'abc');");
 }
+
+#[test]
+fn issue_6732_1() {
+    test(
+        "
+    if (false) {
+        foo(function () {
+            var module = {};
+            return module;
+        });
+    }
+    ",
+        "",
+    );
+}
+
+#[test]
+fn issue_6732_2() {
+    test(
+        "
+    if (false) {
+        function foo() {
+            var module = {};
+            return module;
+        };
+    }
+    ",
+        "var foo;",
+    );
+}

crates/swc_ecma_utils/src/lib.rs

@@ -494,8 +494,6 @@ impl Visit for Hoister {
 
     fn visit_fn_decl(&mut self, f: &FnDecl) {
         self.vars.push(f.ident.clone());
-
-        f.visit_children_with(self)
     }
 
     fn visit_pat(&mut self, p: &Pat) {
@@ -513,6 +511,8 @@ impl Visit for Hoister {
 
         v.visit_children_with(self)
     }
+
+    fn visit_fn_expr(&mut self, _n: &FnExpr) {}
 }
 
 #[derive(Debug, Clone)]