class RuboCop::Cop::Packaging::RequireHardcodingLib

def on_new_investigation

Processing of the AST happens here.

https://github.com/rubocop-hq/rubocop/blob/343f62e4555be0470326f47af219689e21c61a37/lib/rubocop/cop/base.rb
More about the `#on_new_investigation` method can be found here:
Extended from the Base class. 
def on_new_investigation
  @file_path = processed_source.file_path
  @file_directory = File.dirname(@file_path)
end