Bash completions in buildFHSUserEnv

When entering a shell with nix-shell -p bazel, I can get tab-completions for Bazel.

However, some bazel rules require buildFHSUserEnv, and if I use a shell.nix as described in the NixOS Wiki:

 { pkgs ? import <nixpkgs> {} }:
 (pkgs.buildFHSUserEnv {
   name = "bazel-userenv-example";
   targetPkgs = pkgs: [

When I enter that shell, I do not get bash completions. Is there a way to enable completions for buildFHSUserEnv as well?