Compile an Elixir dependency as you change it

In an Elixir project, the dependencies are one-time compiles. That makes sense when you know the dependency is not going to change. It stops making sense, however, when you need to explore how a dependency works by adding debug statements like IO.puts. Or when you find something in a dependency you want to change and need to test that change in an application.

In those cases Elixir provides the facility to compile a dependency each time it has a change in one of the component files just like how compilation in your mix app works. You can enable this by providing a path to the location of the dependency in the mix.exs file:

defp deps do
  [
    ...
    {:wallaby, '~> 0.16.1', path: 'deps/wallaby'}
    ...
  ]
end

In this case the path is set to the local deps dir, where the dependency already exists, but you can also set it to a working directory for that library.