Raise FrozenError for frozen objects when trying to write to a

non-database-backed attribute.

Writing to database-backed attributes after freezing an object would
raise FrozenError, but wouldn't raise FrozenError for user-defined
attributes.

Fixes #37208

activemodel/CHANGELOG.md

@@ -1,3 +1,14 @@
+*   Raise FrozenError when trying to write attributes that aren't backed by the database on an object that is frozen:
+
+        class Animal
+          include ActiveModel::Attributes  
+          attribute :age 
+        end
+        
+        animal = Animal.new
+        animal.freeze 
+        animal.age = 25 # => FrozenError, "can't modify a frozen Animal"
+          
 *   Add *_previously_was attribute methods when dirty tracking. Example:
 
         pirate.update(catchphrase: "Ahoy!")

activemodel/lib/active_model/attributes.rb

@@ -48,6 +48,7 @@ module ActiveModel
           ) do |temp_method_name, attr_name_expr|
             generated_attribute_methods.module_eval <<-RUBY, __FILE__, __LINE__ + 1
               def #{temp_method_name}(value)
+                raise FrozenError, "can't modify frozen #{self.class.name}" if frozen?
                 name = #{attr_name_expr}
                 write_attribute(name, value)
               end

activemodel/test/cases/attributes_test.rb

@@ -107,5 +107,12 @@ module ActiveModel
 
       assert_equal attributes, new_attributes
     end
+
+    test "can't modify attributes if frozen" do
+      data = ModelForAttributesTest.new
+      data.freeze
+      assert data.frozen?
+      assert_raise(FrozenError) { data.integer_field = 1 }
+    end
   end
 end