fix corner case with parentheses (#4409)

fixes #4408

1 files changed, 3 insertions, 5 deletions

diff --git a/lib/output.js b/lib/output.js
index 7bb27d9b..3d8d74c9 100644
--- a/lib/output.js
+++ b/lib/output.js
@@ -1198,11 +1198,9 @@ function OutputStream(options) {
         // need to take some precautions here:
         //    https://github.com/mishoo/UglifyJS/issues/60
         if (noin) node.walk(new TreeWalker(function(node) {
-            if (parens || node instanceof AST_Scope) return true;
-            if (node instanceof AST_Binary && node.operator == "in") {
-                parens = true;
-                return true;
-            }
+            if (parens) return true;
+            if (node instanceof AST_Binary && node.operator == "in") return parens = true;
+            if (node instanceof AST_Scope && !(node instanceof AST_Arrow && node.value)) return true;
         }));
         node.print(output, parens);
     }