eww.nix

# get the all-cabal-files .git directory
let
  url =  "https://github.com/commercialhaskell/all-cabal-files";
  displayrev = "e1017e420cf649cb6850d0b499cae591d888a9dd"; # rev of the 'display' branch commit
  # 1vnc..x4 = echo -n ${url} | nix-hash --flat --base32 --type sha256
  path = "${builtins.getEnv "HOME"}/.cache/nix/gitv2/1vncd1k9gq9imn78zxzp0kf2bphlyph471vsr2wk3sk65xi9w1x4";
in
  builtins.deepSeq (builtins.deepSeq
    (builtins.fetchGit { inherit url; rev = displayrev; ref = "display"; }) # first: make display branch checkout work
    (builtins.fetchGit { inherit url; rev = displayrev; ref = "hackage"; }) # then fetch hackage branch
  ) path