a new version of glib is in all-packages.nix:
glib_2_28 = callPackage ../development/libraries/glib/2.28.x.nix {}
but the corresponding 2.28.x.nix is missing ... nix-env reports
error: getting status of
`/etc/nixos/nixpkgs/pkgs/development/libraries/glib/2.28.x.nix': No such file
or directory