marshal.c: shallow freeze user objects

When `freeze: true` argument is passed.

[Bug #19427]

marshal.c

@@ -2155,7 +2155,12 @@ r_object_for(struct load_arg *arg, bool partial, int *ivp, VALUE extmod, int typ
                 marshal_compat_t *compat = (marshal_compat_t*)d;
                 v = compat->loader(klass, v);
             }
-            if (!partial) v = r_post_proc(v, arg);
+            if (!partial) {
+                if (arg->freeze) {
+                    OBJ_FREEZE(v);
+                }
+                v = r_post_proc(v, arg);
+            }
         }
         break;
 
@@ -2180,6 +2185,9 @@ r_object_for(struct load_arg *arg, bool partial, int *ivp, VALUE extmod, int typ
             load_funcall(arg, v, s_mload, 1, &data);
             v = r_fixup_compat(v, arg);
             v = r_copy_ivar(v, data);
+            if (arg->freeze) {
+                OBJ_FREEZE(v);
+            }
             v = r_post_proc(v, arg);
             if (!NIL_P(extmod)) {
                 if (oldclass) append_extmod(v, extmod);

spec/ruby/core/marshal/shared/load.rb

@@ -141,16 +141,14 @@ describe :marshal_load, shared: true do
       end
 
       ruby_bug "#19427", "3.1"..."3.3" do
-        ruby_bug "#19427", "3.1"..."3.4" do # https://bugs.ruby-lang.org/issues/19427#note-15
-          it "returns frozen object having #_dump method" do
-            object = Marshal.send(@method, Marshal.dump(UserDefined.new), freeze: true)
-            object.should.frozen?
-          end
+        it "returns frozen object having #_dump method" do
+          object = Marshal.send(@method, Marshal.dump(UserDefined.new), freeze: true)
+          object.should.frozen?
+        end
 
-          it "returns frozen object responding to #marshal_dump and #marshal_load" do
-            object = Marshal.send(@method, Marshal.dump(UserMarshal.new), freeze: true)
-            object.should.frozen?
-          end
+        it "returns frozen object responding to #marshal_dump and #marshal_load" do
+          object = Marshal.send(@method, Marshal.dump(UserMarshal.new), freeze: true)
+          object.should.frozen?
         end
 
         it "returns frozen object extended by a module" do