fix corner case in `dead_code` (#4378)

fixes #4377

1 files changed, 25 insertions, 0 deletions

diff --git a/test/compress/async.js b/test/compress/async.js
index 71df2449..8b7f596e 100644
--- a/test/compress/async.js
+++ b/test/compress/async.js
@@ -471,3 +471,28 @@ issue_4359: {
     expect_stdout: "PASS"
     node_version: ">=8"
 }
+
+issue_4377: {
+    options = {
+        dead_code: true,
+        inline: true,
+        side_effects: true,
+    }
+    input: {
+        console.log(typeof function() {
+            return function() {
+                f;
+                async function f() {}
+                return f();
+            }();
+        }().then);
+    }
+    expect: {
+        console.log(typeof function() {
+            return f();
+            async function f() {}
+        }().then);
+    }
+    expect_stdout: "function"
+    node_version: ">=8"
+}