Dynamically alias modules at compile time in Elixir with mox

dynamic_alias.ex

defmodule DynamicAlias do
  @moduledoc """
  Helper macro to call the alias dynamically. This will allow developers to
  stub the testing environment with a mock or use different modules with
  different configuration without the need to use a runtime impl function.

  Please note that this only works in compile time. Do not provide any runtime
  specific configuration here.
  """

  defmacro __using__(_env) do
    mod = __MODULE__

    quote do
      require unquote(mod)
      import unquote(mod)
    end
  end

  @doc """
  Aliases a function dynamically in a module.

  ## Parameters
  - module: The dynamic function which will get you the module name.
  (Don't use module attributes) as they are not available in here.
  - options: All options accepted by `alias/2` like `:as` 

  ## Examples

  ```elixir
  defmodule MyModule do
    use DynamicAlias

    dynamic_alias :my_app, :calendar_impl, Calendar.ISO, as: Calendar

    def utc_now do
      DateTime.utc_now(Calendar)
    end
  end
  ```
  """
  defmacro dynamic_alias(app, key_or_path, default, opts \\ []) do
    module = Application.get_env(app, key_or_path, default)

    quote do
      alias unquote(module), unquote(opts)
    end
  end
end