More Dependencies

Most people think that Erlang has just runtime dependencies. For
the most part this is true. However, Erlang also has two types of
compile time dependencies. The first is the ".hrl" files that are
included into a module. The second type is ".erl" files that
implement a parse transform. Both of these types of files
represent compile time dependencies. For the most part its simple
enough to make sure the include and code path information is
set. However, its much more difficult to make sure that if one of
these types of files change all of its dependencies are changed
as well. I think that the easiest way to handle this would be to
simply look at the ast of a compiled file during the compilation
process and extract the includes and the parse transform
information from that ast. Unfortunately, it means knowing much
more about a dependent OTP application then the build system
currently knows. It would definitely need to happen after the high
level runtime dependency mapping takes place. I think, for now, I
will stick with just handling the runtime dependencies and making
sure that the build time dependencies have the right path
information available. Once the system gets out in the wild and I
start getting feedback I may modify it to be a little smarter
about the compile time dependencies.