fix corner cases with `arguments` (#4481)

fixes #4480

1 files changed, 14 insertions, 4 deletions

diff --git a/lib/scope.js b/lib/scope.js
index 0c35b0dd..4660c787 100644
--- a/lib/scope.js
+++ b/lib/scope.js
@@ -265,10 +265,7 @@ AST_Toplevel.DEFMETHOD("figure_out_scope", function(options) {
             }
             if (!sym) {
                 sym = self.def_global(node);
-            } else if (name == "arguments"
-                && sym.orig[0] instanceof AST_SymbolFunarg
-                && !(sym.orig[1] instanceof AST_SymbolFunarg)
-                && !(sym.scope instanceof AST_Arrow)) {
+            } else if (name == "arguments" && is_arguments(sym)) {
                 var parent = tw.parent();
                 if (parent instanceof AST_Assign && parent.left === node
                     || parent instanceof AST_Unary && unary_side_effects[parent.operator]) {
@@ -297,6 +294,13 @@ AST_Toplevel.DEFMETHOD("figure_out_scope", function(options) {
             node.reference(options);
             return true;
         }
+        if (node instanceof AST_VarDef) {
+            if (node.value && node.name.name == "arguments") {
+                var sym = node.name.scope.resolve().find_variable("arguments");
+                if (sym && is_arguments(sym)) sym.scope.uses_arguments = 3;
+            }
+            return;
+        }
     });
     self.walk(tw);
 
@@ -322,6 +326,12 @@ AST_Toplevel.DEFMETHOD("figure_out_scope", function(options) {
         }
     }));
 
+    function is_arguments(sym) {
+        return sym.orig[0] instanceof AST_SymbolFunarg
+            && !(sym.orig[1] instanceof AST_SymbolFunarg || sym.orig[2] instanceof AST_SymbolFunarg)
+            && !(sym.scope instanceof AST_Arrow);
+    }
+
     function redefine(node, scope) {
         var name = node.name;
         var old_def = node.thedef;