From c8b0f685ee62fe4920b2b4bdaa0d6c17c8a4e18f Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Mon, 4 Oct 2021 17:42:46 +0100
Subject: [PATCH] fix corner case in `merge_vars` (#5143)

fixes #5142
---
 lib/compress.js          |  2 +-
 test/compress/classes.js | 31 +++++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/lib/compress.js b/lib/compress.js
index 3c0bf537..0f567f57 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -5694,7 +5694,7 @@ merge(Compressor.prototype, {
             if (node instanceof AST_Call) {
                 var exp = node.expression;
                 var tail = exp.tail_node();
-                if (!(tail instanceof AST_LambdaExpression)) {
+                if (!is_lambda(tail)) {
                     descend();
                     return mark_expression(exp);
                 }
diff --git a/test/compress/classes.js b/test/compress/classes.js
index 5ed30024..2ac97b02 100644
--- a/test/compress/classes.js
+++ b/test/compress/classes.js
@@ -2066,3 +2066,34 @@ issue_5082_2: {
     expect_stdout: "PASS"
     node_version: ">=12"
 }
+
+issue_5142: {
+    options = {
+        evaluate: true,
+        merge_vars: true,
+        reduce_vars: true,
+        toplevel: true,
+    }
+    input: {
+        var a = 0, b;
+        if (++a)
+            new class {
+                p = b = null;
+                constructor(c) {
+                    console.log(c ? "FAIL" : "PASS");
+                }
+            }(b, a);
+    }
+    expect: {
+        var a = 0, b;
+        if (++a)
+            new class {
+                p = b = null;
+                constructor(c) {
+                    console.log(c ? "FAIL" : "PASS");
+                }
+            }(b, 1);
+    }
+    expect_stdout: "PASS"
+    node_version: ">=12"
+}