According to NixOS Wiki, for flakes in git repos, only files in the working tree will be copied to the store. Given that we are migrating our repos from using shell.nix to use flake.nix, this issue might be redundant.

No, we still need to ignore more files then what is left in the working tree.

So it may be that we don't have to ignore .git, but we still have to ignore all other files. For example:

  src = nix-gitignore.gitignoreSource [
    # The `.git` itself should be ignored
    ".git"
    # Non-build files
    "/nodemon.json"
    # Hidden files
    "/.*"
    # Nix files
    "/*.nix"
    # Benchmarks
    "/benches"
    # Docs
    "/docs"
    # Tests
    "/tests"
    "/jest.config.js"
  ] ./.;

So this issue isn't redundant.