fix corner case in `unused` (#4405)

fixes #4404

1 files changed, 9 insertions, 1 deletions

diff --git a/lib/compress.js b/lib/compress.js
index a3842bed..1249e620 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -5860,7 +5860,15 @@ merge(Compressor.prototype, {
                 if (def.scope === self) assignments.add(def.id, node);
             }
             var node_def, props = [], sym = assign_as_unused(node, props);
-            if (sym && self.variables.get(sym.name) === (node_def = sym.definition())) {
+            if (sym && self.variables.get(sym.name) === (node_def = sym.definition())
+                && !(is_arguments(node_def) && !all(self.argnames, function(argname) {
+                    return !argname.match_symbol(function(node) {
+                        if (node instanceof AST_SymbolFunarg) {
+                            var def = node.definition();
+                            return def.references.length > def.replaced;
+                        }
+                    }, true);
+                }))) {
                 props.forEach(function(prop) {
                     prop.walk(tw);
                 });