Fix rb_define_variable

Author: sue445

_tools/ruby_h_to_go/lib/ruby_h_to_go/argument_definition.rb

@@ -49,6 +49,8 @@ def cast_to_cgo
         return go_name if type == "void" && length == 2
 
         return "(#{"*" * length}#{cast_to_cgo_type(type)})(unsafe.Pointer(#{go_name}))"
+      when :in_ref
+        return "(*#{cast_to_cgo_type(type)})(#{go_name})"
       end
 
       "#{cast_to_cgo_type(type)}(#{go_name})"

_tools/ruby_h_to_go/spec/ruby_h_to_go/function_definition_spec.rb

@@ -469,6 +469,39 @@
 
       it { should eq go_content }
     end
+
+    context "rb_define_variable" do
+      let(:definition) do
+        RubyHeaderParser::FunctionDefinition.new(
+          name:       "rb_define_variable",
+          definition: "void rb_define_variable(const char *name, VALUE *var)",
+          typeref:    typedef(type: "void"),
+          args:       [
+            argument(type: "char", name: "name", pointer: :ref),
+            argument(type: "VALUE", name: "var", pointer: :in_ref),
+          ],
+        )
+      end
+
+      let(:go_content) do
+        <<~GO
+          // RbDefineVariable calls `rb_define_variable` in C
+          //
+          // Original definition is following
+          //
+          //	void rb_define_variable(const char *name, VALUE *var)
+          func RbDefineVariable(name string, v *VALUE)  {
+          char, clean := string2Char(name)
+          defer clean()
+
+          C.rb_define_variable(char, (*C.VALUE)(v))
+          }
+
+        GO
+      end
+
+      it { should eq go_content }
+    end
   end
 
   describe "#go_function_name" do