[Nix-dev] change in HEAD can render a system unbootable

[Michael Alan Dorman]

Since this is something of a hair-on-fire issue, I wanted to bring it up
on-list as well as in the bug tracker to make sure it gets some
exposure.

As reported in https://github.com/NixOS/nixpkgs/issues/12949, there's a
recent change in HEAD that requires some significant effort to recover
from.  It would be good to get the guilty change either reverted or
amended so it won't break things.

Mike.