Sounds like you want to define some shared behaviour that can be applied across a set of controllers? Phoenix doesn't have "nested" controllers like you describe, but you might be able to do what you want using a plug. Something like:
# lib/your_app_web/controllers/user_sidebar.ex
defmodule YourAppWeb.UserSidebar do
def load_sidebar(conn, _params) do
data = SomeModule.whatever_loads_your_sidebar_data()
assign(conn, :sidebar, data)
end
end
# then in router.ex:
import YourAppWeb.UserSidebar
pipeline :users do
plug :load_sidebar
end
scope "/users", YourAppWeb do
pipe_through [:browsers, :user]
get "settings/privacy", SettingsController, :privacy
# and all other routes that need this sidebar
# …
end
Then in your controller action `SettingsController.privacy/2`, the incoming `conn` will already have `sidebar` assigned because it's been passed through `load_sidebar`.
Remember that an HTTP request/response cycle in Phoenix is fundamentally just a list of transformations that are applied to a `%Plug.Conn{}`. If you want the same behaviour to apply to multiple controller actions, you can just define that behaviour in a plug function (i.e. a two-arity function that takes and returns a conn), then pass your conn through that plug before it reaches your controller actions.