From 4d6771b9b1d89f0b49625795a92267d6e59dd064 Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Tue, 7 Jan 2020 19:34:16 +0800
Subject: fix corner case in `collapse_vars` (#3672)

fixes #3671
---
 lib/compress.js                |  2 +-
 test/compress/collapse_vars.js | 27 +++++++++++++++++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/lib/compress.js b/lib/compress.js
index 7e55da5a..03587359 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -1367,7 +1367,7 @@ merge(Compressor.prototype, {
                 if (replace_all) return false;
                 return node instanceof AST_SymbolRef
                     && !node.is_declared(compressor)
-                    && !(parent instanceof AST_Assign && parent.left === node);
+                    && !(parent instanceof AST_Assign && parent.operator == "=" && parent.left === node);
             }
 
             function in_conditional(node, parent) {
diff --git a/test/compress/collapse_vars.js b/test/compress/collapse_vars.js
index a5975279..c3832d43 100644
--- a/test/compress/collapse_vars.js
+++ b/test/compress/collapse_vars.js
@@ -7464,3 +7464,30 @@ issue_3651: {
     }
     expect_stdout: "PASS"
 }
+
+issue_3671: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var a = 0;
+        try {
+            a++;
+            A += 0;
+            a = 1 + a;
+        } catch (e) {
+            console.log(a);
+        }
+    }
+    expect: {
+        var a = 0;
+        try {
+            a++;
+            A += 0;
+            a = 1 + a;
+        } catch (e) {
+            console.log(a);
+        }
+    }
+    expect_stdout: "1"
+}
-- 
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