You could try out exsync for your code reloading:

It will recompile path dependencies for you when you make the changes.

As this is a top result on Google when searching for auto recompiling dependencies, I just wanted to leave a solution that doesn’t require a third party library (not sure if this was possible when the question was originally asked). This is for Phoenix apps running live_reload, if not, then exsync is still a good option.

You’ve got two projects my_app and my_dep. In my_app/mix.exs you’ve got:

    defp deps do
      {:my_dep, path: "../my_dep"}
      ..
    end

In your config/dev.exs:

    config :my_app, MyApp.Endpoint,
      live_reload: [
        patterns: [
          # make sure you have patterns that work for either app, they should be relative 
          # to the root of a project, the same pattern can match both apps. 
          # So don't do '~r"../core_dep/priv"', that'll be ignored, do: '~r"priv"'
        ]
      reloadable_apps: [:my_dep, :my_app]

and

    parent_path =
      __ENV__.file
      |> Path.dirname()
      |> Path.join("../..")
      |> Path.expand()

    config :phoenix_live_reload, :dirs, [
      Path.join([parent_path, "my_dep"]),
      Path.join([parent_path, "my_app"])
    ]

Now your webpage update with changes made to either app.

Recompile does only ever recompile modules of the current application/project.

In my opinion, you should not rely on anything to recompile your dependencies, except for mix deps.compile --force.