From 63f16e4616099752fdf6e16aa25dfb2b9dcea3d0 Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Tue, 17 May 2022 19:41:05 +0100
Subject: [PATCH] fix corner case in `merge_vars` (#5452)

fixes #5451
---
 lib/compress.js             |  7 +++++--
 test/compress/const.js      |  6 +++---
 test/compress/let.js        |  6 +++---
 test/compress/merge_vars.js | 22 ++++++++++++++++++++++
 4 files changed, 33 insertions(+), 8 deletions(-)

diff --git a/lib/compress.js b/lib/compress.js
index 4235617d..55c8f854 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -6183,8 +6183,11 @@ Compressor.prototype.compress = function(node) {
                 return true;
             }
             if (node instanceof AST_Scope) {
-                var parent = tw.parent();
-                var in_iife = parent && parent.TYPE == "Call" && parent.expression === node;
+                var in_iife = false;
+                if (node instanceof AST_LambdaExpression && !node.name) {
+                    var parent = tw.parent();
+                    in_iife = parent && parent.TYPE == "Call" && parent.expression === node;
+                }
                 if (!in_iife) {
                     push();
                     segment.block = node;
diff --git a/test/compress/const.js b/test/compress/const.js
index 9601c588..8178747d 100644
--- a/test/compress/const.js
+++ b/test/compress/const.js
@@ -184,12 +184,12 @@ merge_vars_2: {
     expect: {
         var a = 0;
         1 && --a,
-        a = function f() {
+        b = function f() {
             const c = a && f;
             c.var += 0;
         }(),
-        void console.log(a);
-        var a;
+        void console.log(b);
+        var b;
     }
     expect_stdout: "undefined"
 }
diff --git a/test/compress/let.js b/test/compress/let.js
index 34308ab8..d0261fc4 100644
--- a/test/compress/let.js
+++ b/test/compress/let.js
@@ -237,12 +237,12 @@ merge_vars_2: {
         "use strict";
         var a = 0;
         1 && --a,
-        a = function f() {
+        b = function f() {
             let c = a && f;
             c.var += 0;
         }(),
-        void console.log(a);
-        var a;
+        void console.log(b);
+        var b;
     }
     expect_stdout: "undefined"
     node_version: ">=4"
diff --git a/test/compress/merge_vars.js b/test/compress/merge_vars.js
index 67635436..d6e95dec 100644
--- a/test/compress/merge_vars.js
+++ b/test/compress/merge_vars.js
@@ -3732,3 +3732,25 @@ issue_5420: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5451: {
+    options = {
+        merge_vars: true,
+        toplevel: true,
+    }
+    input: {
+        A = 1;
+        var a = 1, b;
+        console.log(function f() {
+            return a-- && f(b = A, b);
+        }());
+    }
+    expect: {
+        A = 1;
+        var a = 1, b;
+        console.log(function f() {
+            return a-- && f(b = A, b);
+        }());
+    }
+    expect_stdout: "0"
+}