cashd

Troubleshooting Nix problems

Common issues encountered when using the Nix development shell, and how to resolve them.

Git worktrees

If nix develop fails with an error like:

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

       error: opening Git repository "/path/to/cashd": unsupported extension name extensions.relativeworktrees (libgit2 error code = 6)

then your Nix is linked against a libgit2 older than 1.9.4. Git 2.48+ writes the extensions.relativeWorktrees config entry when a worktree is created with relative paths (git worktree add --relative-paths, or with worktree.useRelativePaths=true), and older libgit2 versions refuse to open a repository that uses it. Nix uses libgit2 to read the flake, so evaluation fails.

[!IMPORTANT] This entry is written to the shared repository config, so once any relative worktree exists, nix develop fails in the main checkout too — not just inside the worktree.

Workarounds

These work today, with any Nix version:

bypass libgit2 with a path: flakeref: nix develop "path:$PWD" (note: this copies the working tree to the store and ignores .gitignore); or
create worktrees with absolute paths (omit --relative-paths); or
clear the extension if you don’t need relative worktrees: git config --unset extensions.relativeWorktrees.

Permanent fix

The fix is in libgit2 1.9.4, so the real solution is a Nix that links against libgit2 1.9.4 or newer. Check which version yours links against:

nix-store -qR "$(readlink -f "$(command -v nix)")" | grep libgit2

[!WARNING] nix upgrade-nix does not help yet. It installs the build from the official nix-fallback-paths, which is still linked against libgit2 1.9.2 — there is no new upstream Nix release with the fix. (On some systems that build is even the exact store path you already have, making the upgrade a no-op.)

nixpkgs has already rebuilt Nix against the fixed libgit2 (e.g. nix-2.34.7+1), so the cleanest path is to reinstall Nix using your usual installation method once it picks up that rebuild, then re-run the grep libgit2 check above to confirm it reports 1.9.4 or newer.

Until then, prefer the workarounds above.

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