Fix modiying class variable to frozen class/module

mrbgems/mruby-metaprog/test/metaprog.rb

@@ -171,7 +171,6 @@ assert('Module#class_variable_set', '15.2.2.4.18') do
       @@foo
     end
   end
-
   assert_equal 99, Test4ClassVariableSet.class_variable_set(:@@cv, 99)
   assert_equal 101, Test4ClassVariableSet.class_variable_set(:@@foo, 101)
   assert_true Test4ClassVariableSet.class_variables.include? :@@cv
@@ -180,6 +179,13 @@ assert('Module#class_variable_set', '15.2.2.4.18') do
   %w[@@ @@1 @@x= @x @ x 1].each do |n|
     assert_raise(NameError) { Test4ClassVariableSet.class_variable_set(n, 1) }
   end
+
+  m = Module.new.freeze
+  assert_raise(FrozenError) { m.class_variable_set(:@@cv, 1) }
+
+  parent = Class.new{ class_variable_set(:@@a, nil) }.freeze
+  child = Class.new(parent)
+  assert_raise(FrozenError) { child.class_variable_set(:@@a, 1) }
 end
 
 assert('Module#class_variables', '15.2.2.4.19') do

src/variable.c

@@ -671,6 +671,7 @@ mrb_mod_cv_set(mrb_state *mrb, struct RClass *c, mrb_sym sym, mrb_value v)
     iv_tbl *t = c->iv;
 
     if (iv_get(mrb, t, sym, NULL)) {
+      mrb_check_frozen(mrb, c);
       iv_put(mrb, t, sym, v);
       mrb_write_barrier(mrb, (struct RBasic*)c);
       return;
@@ -698,6 +699,7 @@ mrb_mod_cv_set(mrb_state *mrb, struct RClass *c, mrb_sym sym, mrb_value v)
     c = cls;
   }
 
+  mrb_check_frozen(mrb, c);
   if (!c->iv) {
     c->iv = iv_new(mrb);
   }

test/t/class.rb

@@ -433,6 +433,25 @@ assert('overriding class variable with a module (#3235)') do
   end
 end
 
+assert('class variable for frozen class/module') do
+  module CVarForFrozenModule
+    freeze
+    assert_raise(FrozenError) { @@cv = 1 }
+  end
+
+  class CVarForFrozenClassA
+    @@a = nil
+    freeze
+  end
+  class CVarForFrozenClassB < CVarForFrozenClassA
+    def a=(v)
+      @@a = v
+    end
+  end
+  b = CVarForFrozenClassB.new
+  assert_raise(FrozenError) { b.a = 1 }
+end
+
 assert('class with non-class/module outer raises TypeError') do
   assert_raise(TypeError) { class 0::C1; end }
   assert_raise(TypeError) { class []::C2; end }