Updating local git repo flake input takes a long time

[legendofmiracles]

Describe the bug

When you have an input with the protocol: git+file and then run nix flake update it'll take a long time, if the repo actually changed. In my case almost 2 minutes. I'm also passing a branch name with ?ref.

Steps To Reproduce

1. make a flake with a git repo as an input, and specify an arbitrary branch
2. run nix flake update
3. It takes quite some time to get the latest commit

Expected behavior

Should be near instant, as there's no network roundtrip nor a lot of data that has to be read from the disk.

nix-env --version output

$ nix-env --version
nix-env (Nix) 2.4pre20210908_3c56f62

Additional context
The input in my example is the nixpkgs repo, maybe it has something to do with that the repo is huge... haven't tried smaller ones yet

[erictapen]

Let's close this in favor of #5280?

[legendofmiracles]

Doesn't seem to be happening anymore for me with this version:

$ nix --version
nix (Nix) 2.5pre20211007_844dd90