From 7d6269e3b826524e340edf274a5e42b2a0ea058a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Donny/=EA=B0=95=EB=8F=99=EC=9C=A4?= <kdy1997.dev@gmail.com>
Date: Wed, 28 Aug 2024 13:32:45 +0900
Subject: [PATCH] fix(es/minifier): Track if a var is used with `in` (#9508)

**Related issue:**

 - Closes https://github.com/swc-project/swc/issues/9499
---
 .changeset/sour-pumpkins-rescue.md                 |  6 ++++++
 crates/swc_ecma_minifier/tests/exec.rs             | 13 +++++++++++++
 crates/swc_ecma_usage_analyzer/src/analyzer/mod.rs |  1 +
 3 files changed, 20 insertions(+)
 create mode 100644 .changeset/sour-pumpkins-rescue.md

diff --git a/.changeset/sour-pumpkins-rescue.md b/.changeset/sour-pumpkins-rescue.md
new file mode 100644
index 00000000000..f576fd24dc2
--- /dev/null
+++ b/.changeset/sour-pumpkins-rescue.md
@@ -0,0 +1,6 @@
+---
+swc_ecma_usage_analyzer: patch
+swc_core: patch
+---
+
+fix(es/minifier): Track if a var is used with `in`
diff --git a/crates/swc_ecma_minifier/tests/exec.rs b/crates/swc_ecma_minifier/tests/exec.rs
index 1ec5f9cc016..4d4acb59c1e 100644
--- a/crates/swc_ecma_minifier/tests/exec.rs
+++ b/crates/swc_ecma_minifier/tests/exec.rs
@@ -11347,6 +11347,19 @@ fn issue_9184_2() {
     );
 }
 
+#[test]
+fn issue_9499() {
+    run_default_exec_test(
+        "
+        const o = {'a': 1, 'b': 2};
+        function fn() {
+            return 'a' in o;
+        }
+        console.log(fn());
+",
+    )
+}
+
 #[test]
 fn issue_9356() {
     run_default_exec_test("console.log((function ({ } = 42) { }).length)");
diff --git a/crates/swc_ecma_usage_analyzer/src/analyzer/mod.rs b/crates/swc_ecma_usage_analyzer/src/analyzer/mod.rs
index c901df71a48..785226e3b81 100644
--- a/crates/swc_ecma_usage_analyzer/src/analyzer/mod.rs
+++ b/crates/swc_ecma_usage_analyzer/src/analyzer/mod.rs
@@ -340,6 +340,7 @@ where
             if e.op == op!("in") {
                 for_each_id_ref_in_expr(&e.right, &mut |obj| {
                     let var = self.data.var_or_default(obj.to_id());
+                    var.mark_used_as_ref();
 
                     match &*e.left {
                         Expr::Lit(Lit::Str(prop)) if prop.value.parse::<f64>().is_err() => {