Use a Nix Flake without Adding it to Git

When I work in my own repositories these days, I always add a Nix flake to the repo so that I can spin up a working development environment on any system with a single command.

What do I do when I’m working in someone else’s repo and they don’t want to adopt Nix flakes?

Normally, I’d just add the file to my copy of the repo and gitignore it locally so I don’t commit my personally-specific files with the rest of my changes.

The problem with Nix flakes is that they don’t work unless you git add flake.nix to your repo. So, I searched for a way to have my own flake.nix file without committing it to Git.

Option 1: Create a wrapper parent directory

Commenter @kesor offered the simplest solution I’ve seen so far: create a parent directory.

If you were working on a repo called examplerepo, you’d structure your directory tree like this:

.
├── examplerepo/ << The actual git repo
├── flake.lock
└── flake.nix

That way, flake.nix and flake.lock sit outside of a git repo.

Then, you run nix develop from the parent directory and do your work in the ./examplerepo folder.

The parent directory doesn’t have to be a git repo, but it can be if you want.

Option 2: Hide changes from git

Silvan Mosberger offered this solution:

git add --intent-to-add flake.nix flake.lock && \
  git update-index --assume-unchanged flake.nix flake.lock

It doesn’t work perfectly, as commands like git reset will undo it, but it effectively hides the flake files from the changeset.

Option 3: Tell Nix to ignore git

Serhii Khoma also showed a workaround where you can tell Nix to ignore the git repository:

nix develop path:.

This seems to be a little slower than the standard git-based version.

And then you can ignore the flake files locally with this command:

echo "flake.nix" >> .git/info/exclude && \
  echo "flake.lock" >> .git/info/exclude

This solution is more robust than the hide changes workaround, though you have to remember to use a different nix develop command than you might be used to.