Trying a theme on a git branch in NixOS: an out-of-store-symlinked nvim config switches before its plugins do

If home-manager links your Neovim config with config.lib.file.mkOutOfStoreSymlink pointing at a working tree, git checkout changes the Lua config right away. The plugins (built through wrapNeovimUnstable / vimPlugins in the system closure) only change on the next nixos-rebuild. Switching branches between, say, a gruvbox and a catppuccin setup therefore leaves nvim broken in between: the Lua calls require("gruvbox") while only catppuccin-nvim is installed, or the other way round.

Rebuild right after checkout, or switch both together, for example with a git worktree for the trial branch or by keeping both colorscheme plugins installed.

Related: a rebuild wrapper that exits on "no staged changes" won't roll the system back after you check out the original branch. Run sudo nixos-rebuild switch --flake .#host directly, or nixos-rebuild switch --rollback if the generation before the trial is still the previous one.