As I am starting out with Erlang I've just added dependencies to the end of my Rebar config and everything just kind of worked. I added each dependency one-by-one and didn't have a problem until I cleaned out the deps folder and tried to recompile. Then I ran into this error:

src/ranch_protocol.erl:none: undefined parse transform 'lager_transform'

I knew that it was working before and that the parse transform wasn't an issue. Turns out the dependency ordering matters! Shouldn't be too big a surprise but Rebar uses the list of dependencies as the ordering for compilation, not any kind of introspection. I just had to put the Lager dependency above Ranch and everything worked out.