From 2cfc6dc21abae8926cc92a48c27499c9cfff2921 Mon Sep 17 00:00:00 2001
From: alexlamsl <alexlamsl@gmail.com>
Date: Thu, 8 Apr 2021 16:08:04 +0800
Subject: [PATCH] fix corner case in `collapse_vars`

fixes #4852
---
 lib/compress.js                |  2 +-
 test/compress/collapse_vars.js | 35 ++++++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/lib/compress.js b/lib/compress.js
index 21eec7c3..911cf554 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -1866,7 +1866,7 @@ merge(Compressor.prototype, {
                             return null;
                         }
                       default:
-                        return;
+                        return handle_custom_scan_order(node, multi_replacer);
                     }
                 }
                 // Replace variable when found
diff --git a/test/compress/collapse_vars.js b/test/compress/collapse_vars.js
index eaff0127..fcc47391 100644
--- a/test/compress/collapse_vars.js
+++ b/test/compress/collapse_vars.js
@@ -8897,3 +8897,38 @@ issue_4806: {
     }
     expect_stdout: "PASS"
 }
+
+issue_4852: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var a = "PASS";
+        (function(b) {
+            switch (b = a) {
+              case 42:
+                try {
+                    console;
+                } catch (b) {
+                    b.p;
+                }
+              case console.log(b):
+            }
+        })("FAIL");
+    }
+    expect: {
+        var a = "PASS";
+        (function(b) {
+            switch (a) {
+              case 42:
+                try {
+                    console;
+                } catch (b) {
+                    b.p;
+                }
+              case console.log(a):
+            }
+        })("FAIL");
+    }
+    expect_stdout: "PASS"
+}