Feature request: add system key metadata to components about component HOT 1 CLOSED

Hi, and thanks for your interest in Component!

One of the goals of the original design is that any individual component should not be aware of any details about the surrounding system, including where it is located in the system map. To add that information, even as metadata, opens up the potential for system details to leak into the component.

On most of the applications I have worked on, I have found that logging components' start/stop does not provide much useful information. If the application starts successfully, then I know that all the components started successfully. If any one component fails, then the application will not start. Either way, it is sufficient to log that the entire system started successfully or not.

That said, it is possible to add the system key to every component without modifying the behavior of update-system. Something like this, called after constructing the system but before start, should work:

(defn add-system-keys-metadata [system]
  (reduce-kv (fn [sys k _]
               (update sys k vary-meta assoc ::system-key k))
             system
             system))

from component.