nix develop fails when lockfile is ignored

[viraptor]

Describe the bug

When I work with a repo where the flake lockfile is ignored, I get:

$ nix develop --show-trace          
warning: Git tree '/some/path' is dirty
warning: updating lock file '/some/path/flake.lock':
• Added input 'flake-utils':
...
evaluating derivation 'git+file:///some/path#devShells.aarch64-darwin.default'The following paths are ignored by one of your .gitignore files:
flake.lock
error:
       … while updating the lock file of flake 'git+file:///some/path'

       error: program 'git' failed with exit code 1

Steps To Reproduce

Use flake with flake.lock in gitignore file.

Expected behavior

Either:

• nix develop doesn't try to commit the changes for ignored files, or
• there's an option for "write updates, but don't commit"

nix-env --version output

nix-env (Nix) 2.13.3

Priorities

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[viraptor]

Actually, I just realised it's a weird one, because I'm not specifying --commit-lock-file, so I'm not sure why git is called in the first place...

[thufschmitt]

Regardless of --commit-lock-file, Nix will stage the flake.lock (as it would be ignored otherwise because Nix doesn't take into account the files that git doesn't know about when working in Git repos).

Possibly, Nix could ignore the .gitignore for that (which would be OK-ish since it only stages an empty file iirc, not the actual flake.lock). Or alternatively you can use nix develop path://$PWD to bypass the Git integration altogether (but that can be costly as it will copy the entire directory content to the store)

[9999years]

Ran into this today! You can kinda work around it with --no-write-lock-file.

--reference-lock-file flake.lock and --output-lock-file flake.lock work on a80fb9f but not on Nix 2.17. (Too lazy to find the exact commit, that's the latest one where CI passes on macOS right now.)

[9999years]

From @edolstra on #9284:

This is intended behaviour. We used to pass --force but we removed that in #6917 due to #5810.

I'm not sure how to fix this...