nix <cmd> --update-input ... fails in detached git worktrees

[spacefrogg]

Describe the bug

nix <cmd> --update-input ... fails when the following conditions come together:

1. when called in a git worktree, i.e. when .git is a file (pointing to the real repository) instead of a directory.
2. when the worktree is clean

It reports the worktree as a shallow clone and that it needs a deep clone to update the inputs.

error: '/path/to/repo' is a shallow Git repository, but a non-shallow repository is needed

       … while fetching the input 'git+file:///path/to/repo'

Steps To Reproduce

1. Enter a git repo with a flake that has inputs.
2. Create a worktree with git worktree add ../workree branch
3. cd ../worktree
4. nix flake lock --update-input <input> or any other command that accepts the --update-input option

Expected behavior

Updates the input.

nix-env --version output

2.4

Workaround

1. Run nix <cmd> --update-input <input> path:., which forces nix to interpret the flake URL as a path and avoids the git+file:// codepath.
2. Modify any tracked file (not necessarily flake.lock) to make the tree dirty, also solves the issue.

[spacefrogg]

Update

It is even worse, I am unable to do anything inside a clean ckeckout as described above. Even a simple nix build .#<package> errors.

[rollf]

This is still valid and doesn't work as of 2.13.6:

[I] rollf@nixos /tmp/
❯ nix-env --version
nix-env (Nix) 2.13.6

# Shallow copy:
[I] rollf@nixos /tmp
❯ git clone --depth 1 https://github.com/NixOS/nixpkgs.git
...
[I] rollf@nixos /tmp
❯ cd nixpkgs/

# "shallow=1" is provided by default:
[I] rollf@nixos /tmp/nixpkgs (master)
❯ nix build -L --show-trace --keep-failed .#hellow
error: flake 'git+file:///tmp/nixpkgs?shallow=1' does not provide attribute 'packages.x86_64-linux.hellow', 'legacyPackages.x86_64-linux.hellow' or 'hellow'
       Did you mean one of hello, below, halloy or jello?

# Works fine in the repo itself:
[N] rollf@nixos /tmp/nixpkgs (master) [1]
❯ nix build -L --show-trace --keep-failed .#hello
[I] rollf@nixos /tmp/nixpkgs (master)
❯ ./result/bin/hello
Hello, world!

# Doesn't work in a worktree:
[I] rollf@nixos /tmp/nixpkgs (master)
❯ git worktree add ../feature-x
...
[I] rollf@nixos /tmp/nixpkgs (master)
❯ cd ../feature-x/
[N] rollf@nixos /tmp/feature-x (feature-x)
❯ nix build -L --show-trace --keep-failed .#hello
error:
       … while fetching the input 'git+file:///tmp/feature-x'

       error: '/tmp/feature-x' is a shallow Git repository, but shallow repositories are only allowed when `shallow = true;` is specified.

# Works fine with the workaround mentioned in ths PR:
[I] rollf@nixos /tmp/feature-x (feature-x) [1]
❯ nix build -L --show-trace --keep-failed path:.#hello
[I] rollf@nixos /tmp/nixpkgs (master)
❯ ./result/bin/hello
Hello, world!

Relevant issue is #3756 which seems to have fixed in with shallow copies per se, but not in worktrees

[wolfgangwalther]

Worktrees are still broken today, tested on nix 2.24.14, 2.28.3 and 2.30pre20250521_76a4d4c2.

The error is slightly different, because it doesn't complain about shallow = true anymore, instead it does this:

error: getting parent of Git commit 'ab8e5cefd63027b2527b8a5a9e8e4cab21ce8dfc': object not found - no match for id (9beb192ef839fb6e2733ce09b0753725ddde72e2)

Note: Lix works very well with worktrees.

[Mic92]

I cannot reproduce this bug:

$ git worktree add /tmp/nix master
$ cd /tmp/nix
$ nix flake lock --update-input nixpkgs
warning: '--update-input' is a deprecated alias for 'flake update' and will be removed in a future version.
warning: updating lock file "/tmp/nix/flake.lock":
• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/f40efe1ce90f9cd692c8d56d9305fa6b9c07f211?narHash=sha256-pHO%2BNWd8wJGDuVJjyyxdgtcmiGhNNKbIIXLMLBPxJTI%3D' (2024-11-30)
  → 'github:NixOS/nixpkgs/fe51d34885f7b5e3e7b59572796e1bcb427eccb1?narHash=sha256-qmmFCrfBwSHoWw7cVK4Aj%2Bfns%2Bc54EBP8cGqp/yK410%3D' (2025-05-22)
$ nix --version
nix (Nix) 2.30.0pre20250521_2a66cef

[Mic92]

Also works with 2.28.3

[Mic92]

Ah. I have to clone the repository as a shallow clone first? No this also works with and without worktree here.

[wolfgangwalther]

Ah. I have to clone the repository as a shallow clone first?

That's how I first reproduced it, but then I got the same errors in my regular worktree, which is not shallow, so I left that part out.

It might be different commands that fail today, for example the following fails for me:

• nix repl .
• nix flake check --all-systems --no-build

[wolfgangwalther]

Here's more details:

nixpkgs3 is a worktree, nixpkgs contains the .git directory.

Works in the main worktree:

~/repos/github/nixpkgs (git)-[...] % nix repl .
Nix 2.28.3
Type :? for help.
Loading installable 'git+file:///[...]/repos/github/nixpkgs?shallow=1#'...
Added 7 variables.
nix-repl>

But not in the detached worktree:

~/repos/github/nixpkgs3 (git)-[master] % nix repl .
Nix 2.28.3
Type :? for help.
error:
       … while fetching the input 'git+file:///[...]/repos/github/nixpkgs3'

       error: getting parent of Git commit 'ab8e5cefd63027b2527b8a5a9e8e4cab21ce8dfc': object not found - no match for id (9beb192ef839fb6e2733ce09b0753725ddde72e2)

I also saw this when using lib.fileset.gitTracked, the stacktrace for that suggested the problem is in builtins.fetchGit, IIRC.

[Mic92]

Also this works for me:

/tmp/nixpkgs-shallow master
% nix repl .
Nix 2.30.0pre20250521_2a66cef
Type :? for help.
Loading installable 'git+file:///tmp/nixpkgs-shallow?shallow=1#'...
Added 7 variables.
nix-repl>
cd /tmp/feature-x
% nix repl .
Nix 2.30.0pre20250521_2a66cef
Type :? for help.
Loading installable 'git+file:///tmp/feature-x#'...
Added 7 variables.
nix-repl>

[Mic92]

Can you provide maybe with a full script that reproduces the issue (maybe also pins nixpkgs)?

[wolfgangwalther]

Ah, I remember, I think the detached worktree needs to be on a different commit than the main worktree. If they are on the same commit, then it doesn't break.

I will put together a reproducer in any case.