Current behavior:

• builtins.fetchTarball currently names the derivation after the url (words after last slash in the url)
• builtins.fetchgit currently always names the derivation git-export
• Hydra nix-prefetch-git currently names the derivation git-export (and has an old standing bug in that script of stripping anything that prefixes on .git instead of just .git folder, so .gitignore would also be deleted
• nixpkgs nix-prefetch-git currently names the derivation after url and rev name

All in all, this leads to a lot of frustration since hashes of those derivations will differ. I'll try to fix the Hydra part (and look into since when nix-prefetch-git is crazy).

Mainly, I would hope that fetchTarball and fetchgit can be used interchangeably and it's currently not possible due to different hardcoded names.

cc @ocharles as he mentioned this recently on IRC
cc @edolstra