From b46c7944c6c840c004eacb06cd4eeab4ac2d8a74 Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Sun, 23 Jan 2022 00:45:11 +0800
Subject: [PATCH] fix corner case in `collapse_vars` (#5310)

fixes #5309
---
 lib/compress.js                |  3 ++-
 test/compress/collapse_vars.js | 35 ++++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/lib/compress.js b/lib/compress.js
index 239bd48e..8db8b6bf 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -2119,7 +2119,8 @@ Compressor.prototype.compress = function(node) {
                         var parent = multi_replacer.parent();
                         if (parent instanceof AST_Sequence && parent.tail_node() !== node) {
                             value_def.replaced++;
-                            return List.skip;
+                            if (rvalue === rhs_value) return List.skip;
+                            return make_sequence(rhs_value, rhs_value.expressions.slice(0, -1));
                         }
                         return rvalue;
                       case 1:
diff --git a/test/compress/collapse_vars.js b/test/compress/collapse_vars.js
index 2c547274..126d4cf8 100644
--- a/test/compress/collapse_vars.js
+++ b/test/compress/collapse_vars.js
@@ -9810,3 +9810,38 @@ issue_5277: {
     }
     expect_stdout: "undefined"
 }
+
+issue_5309_1: {
+    options = {
+        collapse_vars: true,
+        conditionals: true,
+        toplevel: true,
+    }
+    input: {
+        if (console)
+            var a = (console.log("PASS"), b), b = a;
+        else
+            console.log("FAIL");
+    }
+    expect: {
+        var a, b;
+        console ? (console.log("PASS"), b = b) : console.log("FAIL");
+    }
+    expect_stdout: "PASS"
+}
+
+issue_5309_2: {
+    options = {
+        collapse_vars: true,
+        toplevel: true,
+    }
+    input: {
+        var a, b;
+        console ? (a = (console.log("PASS"), b), b = a) : console.log("FAIL");
+    }
+    expect: {
+        var a, b;
+        console ? (console.log("PASS"), b = b) : console.log("FAIL");
+    }
+    expect_stdout: "PASS"
+}