What does these compile time warning means?

Question

I am newbie to erlang chicagoboss. I have just created a small project in erlang, and now wanted to update CB. Since I am updating only ChicagoBoss to its latest version i.e. 0.8.14. But While compiling/ running ./rebar get-deps getting following warnings.

I'm not getting what does it mean?

WARN:  Expected /home/user/workspace/ChicagoBoss/deps/mimetypes to be an app dir (containing ebin/*.app), but no .app found.
WARN:  Expected /home/user/workspace/ChicagoBoss/deps/cowlib to be an app dir (containing ebin/*.app), but no .app found.
WARN:  Expected /home/user/workspace/ChicagoBoss/deps/ranch to be an app dir (containing ebin/*.app), but no .app found.
WARN:  Expected /home/user/workspace/ChicagoBoss/deps/cowlib to be an app dir (containing ebin/*.app), but no .app found.
WARN:  Expected /home/user/workspace/ChicagoBoss/deps/ranch to be an app dir (containing ebin/*.app), but no .app found.

There're many warnings like these one. What I have understand some file .app not found. Since my questions are :

• What does .app do, does it save any configurations?
• Would it cause any issues?
• I am not updating erlang, my current version of erlang is R16B01. Does those warnings have anything to do with the erlang version?

Answer 1

As you guess it, all the listed directory should contain a directory ebin containing a file with the extension .app. These files are use by the erlang vm to start applications. In your case, they are all the applications on which chicagoboss depends. The build command should have done everything for you. Obviously something went wrong, maybe you can reload the dependencies:

remove downloaded dependencies
./rebar delete-deps
reload dependencies
./rebar get-deps 

Answer 2

There's nothing wrong here; rather, these are just warnings that the rebar build tool issues when it starts to build a system but hasn't yet retrieved and built the project dependencies. The warnings won't occur again once rebar downloads and builds them.