It took me a bit to figure out what was wrong here, and I don't think it is documented
anywhere. Here are a couple issues I ran into:

1. If custom colors are defined in ~/.ripgreprc, eg. --colors=path:fg:cyan etc. then
   font-locking and other functions in the rg-results buffer don't work.

2. Using xterm-color-filter also breaks rg's compilation (from xterm-color library)
   I usually use xterm-color-filter in my compilation-start-hook to interpret shell escapes,
   however, since rg (like ag.el) relies on shell escapes for parsing, font-lock/other functions
   also break in the rg-results buffer.

Quick fix is to remove xterm-color support around rg-run

(define-advice rg-run (:around (orig-fn &rest args) "no-xterm-color")
  (let ((compilation-start-hook
         (remove 'my-compilation-start-hook compilation-start-hook))
        compilation-environment)
    (apply orig-fn args)))

It looks like it would probably be out-of-the question to add support to rg-results that
didn't rely on escape codes, but it might be helpful to mention incompatibilities somewhere.