❯ cd $(mktemp -d)
❯ git init
Initialized empty Git repository in /tmp/tmp.4OVTSSw0qw/.git/
❯ echo $RANDOM > file
❯ git add file
❯ git commit --allow-empty-message --message ""
[main (root-commit) e6cc350] 
 1 file changed, 1 insertion(+)
 create mode 100644 file
❯ nix-instantiate --eval -E 'builtins.fetchGit ./.'
error:
       … while calling the 'fetchGit' builtin
         at «string»:1:1:
            1| builtins.fetchGit ./.
             | ^

       error: path '/nix/store/2mph3l2j090y9nvjxb17fdw5wkdvh6z9-source' is not valid

❯ nix-instantiate --eval -E 'builtins.fetchGit ./.'
{ lastModified = 1708369413; lastModifiedDate = "20240219190333"; narHash = "sha256-cXK7rwPAHhUlmfVWbfldKqwMORil5JJRwGfyNRUPwIc="; outPath = "/nix/store/2mph3l2j090y9nvjxb17fdw5wkdvh6z9-source"; rev = "e6cc3500a0bc2bbc3d13937d752a8cad5f5a35bf"; revCount = 1; shortRev = "e6cc350"; submodules = false; }