I’m creating a NIF, and having some issues around packaging.

• I started with an empty Elixir app, added the NIF source in its own directory, the appropriate task to mix.exs to build shared library into priv, and the wrapper module with @on_load of :erlang.load_nif('priv/foo.so', nil)

• That worked: I could iex -S mix run --no-halt then exercise the NIF using Foo.func(...); also foo’s tests worked.

• I want to package this as a library that can just be pulled in as a normal dependency. It’s just simple functions, no need for its own application or any processes. So I deleted lib/foo_app.ex and lib/foo_app/application.ex, and in mix.exs removed the mod: entry from the application. mix compile and mix test both work.

• Now for the problems: using it. I create a new empty application, add the dependency {:foo, path: "../foo", app: false}. Compile works, but when I try to run (or test), the load of the NIF fails, because it’s not in priv relative to the executing project location, but rather in _build/dev/lib/local_dependency

• It seems that maybe to load the NIF I should use Application.app_dir(:foo, "priv") but that gives an error about unknown application, while :code.priv_dir(:foo) gives :bad_name. Also, I note that mix release does not copy the NIF lib at all, not even if I add Mix.Project.build_structure to the end of the compile mix task after priv/foo.so is created.

• So maybe I have to have an empty dummy application in the lib project, just to make all the build parts happy? And indeed, adding back a dummy app, setting the mod: to point to it, etc, makes things work. But of course the dummy app needs a start/2 with a return of the right form, so:

defmodule Foo.App do
  use Application
  def start(_, _) do
    Supervisor.start_link([], [strategy: :one_for_one])
  end
end

It seems silly to have to implement a do-nothing supervisor in order for the NIF lib to be copied and able to be located. Isn’t there a better way to structure and pull in this lib???