Fix alias_attribute to ignore methods defined in parent classes

Fix: rails#52144

When defining regular attributes, inherited methods aren't overriden,
however when defining aliased attributes, inherited methods aren't
considered.

This behavior could be debatted, but that was the behavior prior
to rails#52118, so I'm restoring it.

Author: byroot

activemodel/lib/active_model/attribute_methods.rb

@@ -312,26 +312,33 @@ def define_attribute_method(attr_name, _owner: generated_attribute_methods, as:
         end
       end
 
-      def define_attribute_method_pattern(pattern, attr_name, owner:, as:) # :nodoc:
+      def define_attribute_method_pattern(pattern, attr_name, owner:, as:, override: false) # :nodoc:
         canonical_method_name = pattern.method_name(attr_name)
         public_method_name = pattern.method_name(as)
 
-        unless instance_method_already_implemented?(public_method_name)
-          generate_method = "define_method_#{pattern.proxy_target}"
+        # If defining a regular attribute method, we don't override methods that are explictly
+        # defined in parrent classes.
+        if instance_method_already_implemented?(public_method_name)
+          # However, for `alias_attribute`, we always define the method.
+          # We check for override second because `instance_method_already_implemented?`
+          # also check for dangerous methods.
+          return unless override
+        end
 
-          if respond_to?(generate_method, true)
-            send(generate_method, attr_name.to_s, owner: owner, as: as)
-          else
-            define_proxy_call(
-              owner,
-              canonical_method_name,
-              pattern.proxy_target,
-              pattern.parameters,
-              attr_name.to_s,
-              namespace: :active_model_proxy,
-              as: public_method_name
-            )
-          end
+        generate_method = "define_method_#{pattern.proxy_target}"
+
+        if respond_to?(generate_method, true)
+          send(generate_method, attr_name.to_s, owner: owner, as: as)
+        else
+          define_proxy_call(
+            owner,
+            canonical_method_name,
+            pattern.proxy_target,
+            pattern.parameters,
+            attr_name.to_s,
+            namespace: :active_model_proxy,
+            as: public_method_name
+          )
         end
       end
 

activerecord/lib/active_record/attribute_methods.rb

@@ -91,7 +91,7 @@ def alias_attribute_method_definition(code_generator, pattern, new_name, old_nam
           raise ArgumentError, "#{self.name} model aliases `#{old_name}`, but `#{old_name}` is not an attribute. " \
             "Use `alias_method :#{new_name}, :#{old_name}` or define the method manually."
         else
-          define_attribute_method_pattern(pattern, old_name, owner: code_generator, as: new_name)
+          define_attribute_method_pattern(pattern, old_name, owner: code_generator, as: new_name, override: true)
         end
       end
 

activerecord/test/cases/attribute_methods_test.rb

@@ -1217,6 +1217,25 @@ def some_method_that_is_not_on_super
     alias_attribute :subject, :title
   end
 
+  test "#alias_attribute override methods defined in parent models" do
+    parent_model = Class.new(ActiveRecord::Base) do
+      self.abstract_class = true
+
+      def subject
+        "Abstract Subject"
+      end
+    end
+
+    subclass = Class.new(parent_model) do
+      self.table_name = "topics"
+      alias_attribute :subject, :title
+    end
+
+    obj = subclass.new
+    obj.title = "hey"
+    assert_equal("hey", obj.subject)
+  end
+
   test "aliases to the same attribute name do not conflict with each other" do
     first_model_object = ToBeLoadedFirst.new(author_name: "author 1")
     assert_equal("author 1", first_model_object.subject)