structuredAttrs is enabled

trying https://github.com/mbbill/undotree/archive/6fa6b57cda8459e1e4b2ca34df702f55242f4e4d.tar.gz
  % Total    % Received % Xferd  Average Speed  Time    Time    Time   Current
                                 Dload  Upload  Total   Spent   Left   Speed
  0      0   0      0   0      0      0      0                              0
100 161.4k   0 161.4k   0      0 358.6k      0                              0
unpacking source archive /nix/var/nix/builds/nix-56809-1416921721/download.tar.gz