fix ActionText::Attachable#as_json to allow options

actiontext/lib/action_text/attachable.rb

@@ -98,11 +98,6 @@ def previewable_attachable?
       false
     end
 
-    # Returns the attachable as JSON with the +attachable_sgid+ included.
-    def as_json(*)
-      super.merge("attachable_sgid" => persisted? ? attachable_sgid : nil)
-    end
-
     # Returns the path to the partial that is used for rendering the attachable
     # in Trix. Defaults to +to_partial_path+.
     #
@@ -142,5 +137,18 @@ def to_rich_text_attributes(attributes = {})
         attrs[:height] = attachable_metadata[:height]
       end.compact
     end
+
+    private
+      def attribute_names_for_serialization
+        super + ["attachable_sgid"]
+      end
+
+      def read_attribute_for_serialization(key)
+        if key == "attachable_sgid"
+          persisted? ? super : nil
+        else
+          super
+        end
+      end
   end
 end

actiontext/test/unit/attachable_test.rb

@@ -40,4 +40,13 @@ class ActionText::AttachableTest < ActiveSupport::TestCase
 
     assert_equal attributes, attachable.as_json
   end
+
+  test "attachable_sgid is included in as_json when only option is nil or includes attachable_sgid" do
+    attachable = ActiveStorage::Blob.create_after_unfurling!(io: StringIO.new("test"), filename: "test.txt", key: 123)
+
+    assert_equal({ "id" => attachable.id }, attachable.as_json(only: :id))
+    assert_equal({ "id" => attachable.id }, attachable.as_json(only: [:id]))
+    assert_equal(attachable.as_json.except("attachable_sgid"), attachable.as_json(except: :attachable_sgid))
+    assert_equal(attachable.as_json.except("attachable_sgid"), attachable.as_json(except: [:attachable_sgid]))
+  end
 end