{ lib, ... }:
let
  duplicateUids =
    entries:
    lib.filterAttrs (_uid: entryNames: builtins.length entryNames > 1) (entryNamesByUid entries);

  entryNamesByUid =
    entries:
    lib.mapAttrs (_uid: uidEntries: lib.unique (map (entry: entry.entry) uidEntries)) (
      lib.groupBy (entry: toString entry.value) entries
    );

in
{
  # Next stable UID: 20005

  type = lib.types.ints.positive;

  checks = [
    {
      assertion = entries: duplicateUids entries == { };
      message = "Multiple entries use the same stable UID.";
    }
  ];
}