patch up #1543 for harmony

fixes #1537

lib/compress.js

@@ -549,6 +549,7 @@ merge(Compressor.prototype, {
                     if (var_decl.value.is_constant()) {
                         var ctt = new TreeTransformer(function(node) {
                             if (node === ref
+                                && !ctt.find_parent(AST_Destructuring)
                                 && !ctt.find_parent(AST_ForIn)) {
                                 return replace_var(node, ctt.parent(), true);
                             }
@@ -581,6 +582,7 @@ merge(Compressor.prototype, {
                             if (unwind) return node;
                             var parent = tt.parent();
                             if (node instanceof AST_Lambda
+                                || node instanceof AST_Destructuring
                                 || node instanceof AST_Try
                                 || node instanceof AST_With
                                 || node instanceof AST_Case

test/compress/collapse_vars.js

@@ -1343,3 +1343,81 @@ issue_1537_for_of: {
         for (k of {prop: 'val'});
     }
 }
+
+issue_1537_destructuring_1: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var x = 1, y = 2;
+        [x] = [y];
+    }
+    expect: {
+        var x = 1;
+        [x] = [2];
+    }
+}
+
+issue_1537_destructuring_2: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var x = foo();
+        [x] = [1];
+    }
+    expect: {
+        var x = foo();
+        [x] = [1];
+    }
+}
+
+issue_1537_destructuring_3: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var x = Math.random();
+        ({p: x = 9} = {v: 1});
+    }
+    expect: {
+        var x = Math.random();
+        ({p: x = 9} = {v: 1});
+    }
+}
+
+issue_1537_destructuring_for_in: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var x = 1, y = 2;
+        (function() {
+            for ([[x], y] in a);
+        })();
+    }
+    expect: {
+        var x = 1, y = 2;
+        (function() {
+            for ([[x], y] in a);
+        })();
+    }
+}
+
+issue_1537_destructuring_for_of: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var x = 1, y = 2;
+        (function() {
+            for ([[x], y] of a);
+        })();
+    }
+    expect: {
+        var x = 1, y = 2;
+        (function() {
+            for ([[x], y] of a);
+        })();
+    }
+}