shut_up_dialyzer.ex

defmodule ShutUpDialyzer do
  defmacro __using__(_opts) do
    quote do
      @on_definition unquote(__MODULE__)
      @before_compile unquote(__MODULE__)
      Module.register_attribute(__MODULE__, :funs, accumulate: true)
    end
  end

  def __on_definition__(%{module: module}, :def, name, args, _guards, _body) do
    fun = Keyword.new([{name, length(args)}])
    Module.put_attribute(module, :funs, fun)
  end

  defmacro __before_compile__(%{module: module}) do
    funs = Module.delete_attribute(module, :funs) |> List.flatten()
    Module.put_attribute(module, :dialyzer, {:nowarn_function, funs})
  end
end

some_module.ex

defmodule SomeModule do
  use ShutUpDialyzer

  def do_something do
    nil
  end
end