From 475f551f2f91d4a1244a1cd47d11887128e01e1e Mon Sep 17 00:00:00 2001
From: alexlamsl <alexlamsl@gmail.com>
Date: Tue, 2 May 2017 23:55:36 +0800
Subject: [PATCH] fix corner case with top-level singular reference

---
 lib/compress.js                |  7 +++----
 test/compress/collapse_vars.js | 18 ++++++++++++++++++
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/lib/compress.js b/lib/compress.js
index bb8a3c1f..884c2007 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -711,7 +711,8 @@ merge(Compressor.prototype, {
                                 return make_node(AST_UnaryPrefix, candidate, candidate);
                             }
                             if (candidate instanceof AST_VarDef) {
-                                if (candidate.name.definition().references.length == 1) {
+                                var def = candidate.name.definition();
+                                if (def.references.length == 1 && (!def.global || compressor.toplevel(def))) {
                                     return maintain_this_binding(parent, node, candidate.value);
                                 }
                                 return make_node(AST_Assign, candidate, {
@@ -779,9 +780,7 @@ merge(Compressor.prototype, {
                     expr.expressions.forEach(extract_candidates);
                 } else if (expr instanceof AST_Definitions) {
                     expr.definitions.forEach(function(var_def) {
-                        if (var_def.value) {
-                            candidates.push(var_def);
-                        }
+                        if (var_def.value) candidates.push(var_def);
                     });
                 } else if (expr instanceof AST_SimpleStatement) {
                     extract_candidates(expr.body);
diff --git a/test/compress/collapse_vars.js b/test/compress/collapse_vars.js
index 75c65147..ef5c19ce 100644
--- a/test/compress/collapse_vars.js
+++ b/test/compress/collapse_vars.js
@@ -2059,3 +2059,21 @@ double_def: {
         (a = a && y)();
     }
 }
+
+toplevel_single_reference: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var a;
+        for (var b in x) {
+            var a = b;
+            b(a);
+        }
+    }
+    expect: {
+        var a;
+        for (var b in x)
+            b(a = b);
+    }
+}