Support global variable target in for loop

lib/natalie/compiler/args.rb

@@ -50,6 +50,8 @@ def transform_arg(arg)
           transform_instance_variable_arg(arg)
         when ::Prism::ClassVariableTargetNode
           transform_class_variable_arg(arg)
+        when ::Prism::GlobalVariableTargetNode
+          transform_global_variable_arg(arg)
         when ::Prism::ConstantTargetNode
           transform_constant_arg(arg)
         when ::Prism::RequiredParameterNode
@@ -174,6 +176,11 @@ def transform_class_variable_arg(arg)
         @instructions << ClassVariableSetInstruction.new(arg.name)
       end
 
+      def transform_global_variable_arg(arg)
+        @instructions << ArrayShiftInstruction.new
+        @instructions << GlobalVariableSetInstruction.new(arg.name)
+      end
+
       def transform_constant_arg(arg)
         @instructions << ArrayShiftInstruction.new
         @instructions << PushSelfInstruction.new

lib/natalie/compiler/pass1.rb

@@ -2671,6 +2671,7 @@ def maximum_arg_count(args)
           %i[
             class_variable_target_node
             constant_target_node
+            global_variable_target_node
             instance_variable_target_node
             local_variable_target_node
             multi_target_node

spec/language/for_spec.rb

@@ -104,6 +104,18 @@ class OFor
     end
   end
 
+  it "allows a global variable as an iterator name" do
+    old_global_var = $var
+    m = [1,2,3]
+    n = 0
+    for $var in m
+      n += 1
+    end
+    $var.should == 3
+    n.should == 3
+    $var = old_global_var
+  end
+
   # 1.9 behaviour verified by nobu in
   # http://redmine.ruby-lang.org/issues/show/2053
   it "yields only as many values as there are arguments" do