fix mrb_mod_cv_set and add test for Module#class_variable_set

src/variable.c

@@ -698,6 +698,8 @@ mrb_cv_get(mrb_state *mrb, mrb_value mod, mrb_sym sym)
 void
 mrb_mod_cv_set(mrb_state *mrb, struct RClass * c, mrb_sym sym, mrb_value v)
 {
+  struct RClass * cls = c;
+
   while (c) {
     if (c->iv) {
       iv_tbl *t = c->iv;
@@ -710,11 +712,11 @@ mrb_mod_cv_set(mrb_state *mrb, struct RClass * c, mrb_sym sym, mrb_value v)
     c = c->super;
   }
 
-  if (!c->iv) {
-    c->iv = iv_new(mrb);
+  if (!cls->iv) {
+    cls->iv = iv_new(mrb);
   }
 
-  iv_put(mrb, c->iv, sym, v);
+  iv_put(mrb, cls->iv, sym, v);
 }
 
 void

test/t/module.rb

@@ -54,6 +54,21 @@ assert('Module#class_variable_get', '15.2.2.4.17') do
   Test4ClassVariableGet.class_variable_get(:@@cv) == 99
 end
 
+assert('Module#class_variable_set', '15.2.2.4.18') do
+  class Test4ClassVariableSet
+    @@foo = 100
+    def foo
+      @@foo
+    end
+  end
+
+  Test4ClassVariableSet.class_variable_set(:@@cv, 99)
+  Test4ClassVariableSet.class_variable_set(:@@foo, 101)
+
+  Test4ClassVariableSet.class_variables.include? :@@cv and
+  Test4ClassVariableSet.class_variable_get(:@@cv) == 99 and
+  Test4ClassVariableSet.new.foo == 101
+end
 
 assert('Module#class_variables', '15.2.2.4.19') do
   class Test4ClassVariables1