From 2cb6454b1f8739e27708a29c5a97610afa2c554e Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Sat, 8 Jun 2024 20:15:37 +0300
Subject: [PATCH] fix corner case in `merge_vars` (#5830)

fixes #5829
---
 lib/compress.js          |  4 +++-
 test/compress/nullish.js | 40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/lib/compress.js b/lib/compress.js
index 664be40da2b..d0babad62b5 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -6719,9 +6719,11 @@ Compressor.prototype.compress = function(node) {
                     segments.consequent = scan_branches(level + 1, condition.left, condition.right).consequent;
                     break;
                   case "||":
-                  case "??":
                     segments.alternative = scan_branches(level + 1, condition.left, null, condition.right).alternative;
                     break;
+                  case "??":
+                    segments.alternative = scan_branches(level + 1, condition.left, condition.right, condition.right).alternative;
+                    break;
                   default:
                     condition.walk(tw);
                     break;
diff --git a/test/compress/nullish.js b/test/compress/nullish.js
index 2f438d45aea..2ef46bcece3 100644
--- a/test/compress/nullish.js
+++ b/test/compress/nullish.js
@@ -344,3 +344,43 @@ issue_5266: {
     ]
     node_version: ">=14"
 }
+
+issue_5829_1: {
+    options = {
+        merge_vars: true,
+    }
+    input: {
+        (function f(a) {
+            var b;
+            (!a ?? (b = 0)) || console.log(b || "PASS");
+        })("FAIL");
+    }
+    expect: {
+        (function f(a) {
+            var b;
+            (!a ?? (b = 0)) || console.log(b || "PASS");
+        })("FAIL");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=14"
+}
+
+issue_5829_2: {
+    options = {
+        merge_vars: true,
+    }
+    input: {
+        (function f(a) {
+            var b;
+            (a ?? (b = 0)) && console.log(b || "PASS");
+        })("FAIL");
+    }
+    expect: {
+        (function f(a) {
+            var b;
+            (a ?? (b = 0)) && console.log(b || "PASS");
+        })("FAIL");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=14"
+}