module Bundler::Plugin::API::Source

def app_cache_path(custom_path = nil)

Note: Do not override if you don't know what you are doing.

installed latter.
The full path where the plugin should cache the gem so that it can be 
def app_cache_path(custom_path = nil)
  @app_cache_path ||= Bundler.app_cache(custom_path).join(app_cache_dirname)
end