I encountered this interesting thing while trying to add more info to Logger messages.

I can get the version of an app by running something like this:

:myapp
        |> Application.spec()
        |> Keyword.get(:vsn)
        |> List.to_string()

However, I thought this calculation maybe is expensive, so I tried to save this at compile time by putting it into a module attribute:

@app_ver :myapp
        |> Application.spec()
        |> Keyword.get(:vsn)
        |> List.to_string()

However I have noticed that Application.spec/1 returns nil at compile time. Is there a way to read and store an application version at compile time? Or is the version only known AFTER compilation?