Plugin formulae should be declared as keg only

[Deleted user]

Plugins that have a bin/ directory end up having these files automatically symlinked by Homebrew into /usr/local/bin. As Athena plugins are not meant to be executed directly, and as that directory does not contain any scripts that should be made globally available, the plugins formulae should be declared as keg_only in order to prevent the symlinking.

This behaviour causes two Athena plugins to have a conflict during installation if they both declare shell scripts with the name name inside bin/, which is a very likely case as Athena plugins are based on filename conventions.