Motivation for this change

I've got some extra vim plugins in my nixpkgs fork (that I haven't upstreamed for different reasons, not fixed, personal etc). When rebasing it often generates conflicts, so I end up using upstream generated.nix and at the end of the rebase call ./pkgs/misc/vim-plugins/update.py .
It can be boring to do so I would like to move this kind of personal list to an overlay.
I modified ./pkgs/misc/vim-plugins/update.py to accept optional input list and output file.
For instance
./pkgs/misc/vim-plugins/update.py -i ~/dotfiles/config/nixpkgs/overlays/vim-plugins-names -o toto.nix

One issue is that I am not sure how to import these in my overlay. It would be nice if generated.nix could be implemented as an overlay so that the same update.py can generate code for nixpkgs and user overlays.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

Notify maintainers

cc @