From 6b603e1a62efe324af67ed6627b50565aed9599c Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Mon, 7 Dec 2020 05:23:53 +0000
Subject: [PATCH] fix corner case in `unused` (#4338)

fixes #4337
---
 lib/compress.js        |  1 +
 test/compress/async.js | 23 +++++++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/lib/compress.js b/lib/compress.js
index 005768b7..09b27635 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -6269,6 +6269,7 @@ merge(Compressor.prototype, {
             }
             return this;
         });
+        def(AST_AsyncFunction, return_null);
         def(AST_Binary, function(compressor, first_in_statement) {
             if (this.operator == "in" && !is_object(this.right)) {
                 var left = this.left.drop_side_effect_free(compressor, first_in_statement);
diff --git a/test/compress/async.js b/test/compress/async.js
index 8da545bd..0f997332 100644
--- a/test/compress/async.js
+++ b/test/compress/async.js
@@ -264,3 +264,26 @@ issue_4335_2: {
     expect_stdout: "PASS"
     node_version: ">=8"
 }
+
+issue_4337: {
+    options = {
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        (function(a) {
+            a();
+        })(async function() {
+            console.log("PASS");
+        });
+    }
+    expect: {
+        (function(a) {
+            (async function() {
+                console.log("PASS");
+            })();
+        })();
+    }
+    expect_stdout: "PASS"
+    node_version: ">=8"
+}
-- 
2.34.1