This option manages what happens to formulae installed by Homebrew, that aren't present in the Brewfile generated by this module, during nix-darwin system activation.
When set to "none" (the default), formulae not present in the generated Brewfile are left installed.
When set to "uninstall", nix-darwin invokes brew bundle [install] with the --cleanup flag. This uninstalls all formulae not listed in generated Brewfile, i.e., brew uninstall is run for those formulae.
When set to "zap", nix-darwin invokes brew bundle [install] with the --cleanup --zap flags. This uninstalls all formulae not listed in the generated Brewfile, and if the formula is a cask, removes all files associated with that cask. In other words, brew uninstall --zap is run for all those formulae.
If you plan on exclusively using nix-darwin to manage formulae installed by Homebrew, you probably want to set this option to "uninstall" or "zap".
one of "none", "uninstall", "zap""none""uninstall"