The things that I dislike about this setup are:
1. `xref-find-definitions` takes me to `/nix/store`, which is a read-only
version of the source code, so I cannot edit it, which doesn't feel lispy.
2. I need to rebuild the derivation when I change something, which also doesn't
feel lispy.
There are ways to circumvent both of these drawbacks, but for now, I'm checking
this in only to later revert it.
069ca63082