cc @kalbasit since he was doing some vim work recently

@jonringer @kalbasit Can this PR get reviewed ?

this seems to be a long standing issue, and it seems like you did your due diligence on investigating a solution. Thanks!

coc-nvim put in configure.packages.plugins.start fails to load for me with this change applied, whereas it works fine with configure.plug.plugins.

Just tested this with a simple config :

neovim.override {
    configure = {
      customRC = ''
        set shiftwidth=2
        set softtabstop=2
        set expandtab
      '';
      packages.myVimPackage = with vimPlugins; {
        start = [
          coc-nvim
        ];
        opt = [ ];
      };
    };
  };

and coc-nvim is loading correctly.
@rvolosatovs Maybe you some custom config in your ~/.config/nvim that is depending on the old broken behavior ?

My main concern is that people have already developed hacks around the pre-existing design, and they might be incompatible with this fix.

that being said, I would rather have "normal path" work fine, than people having to search through issues and PRs to get their vim workflow going. The individuals who have already developed hacks likely have context to what they did and why it might be wrong.

@timokau might have some insights. Otherwise it looks good.

I'll give this PR a try in my vim config and report back.

@megheaiulian I can reproduce the issue with such minimal shell.nix:

with import (builtins.fetchTarball https://github.com/NixOS/nixpkgs/archive/5d2ea07f02ba60aa7af2388381f14dd62a0978dc.tar.gz) {};
stdenv.mkDerivation {
  name = "env";
  buildInputs = [
    (neovim.override {
      configure = {
        customRC = ''
          set shiftwidth=2
          set softtabstop=2
          set expandtab

          call coc#config('coc', {
          \ 'preferences': {
          \   'codeLens.enable': "true",
          \   'colorSupport': "true",
          \   'extensionUpdateCheck': "never",
          \   'formatOnSaveFiletypes': [ "go" ],
          \ },
          \ 'suggest': {
          \   'acceptSuggestionOnCommitCharacter': "true",
          \   'enablePreview': "true",
          \   'timeout': 2000,
          \   'triggerAfterInsertEnter': "true",
          \ },
          \})
        '';
        packages.myVimPackage = with vimPlugins; {
          start = [
            coc-nvim
          ];
          opt = [ ];
        };
        # Works fine with:
        #plug.plugins = with vimPlugins; [
        #  coc-nvim
        #];
      };
    })
  ];
}

I'm getting this error with package system:

Error detected while processing /nix/store/0jgkc9zhi5h40xqkkd27wa343mshzx3l-vimrc:
line   30:
E117: Unknown function: coc#config

While with plug implementation it just works.

EDIT: Replaced <nixpkgs> by link to 5d2ea07 tarball

It's been so long I forgot what was breaking on my end.
But I removed my workaround and various plugins seem to work still.
Success?
Happy to test specific things.

@rvolosatovs After further investigating this I think your expectations are wrong.
This works exactly like placing that customRC in your .config/nvim/init.vim and having coc-nvim in ./config/nvim/pack/myVimPackage/start/coc-nvim. The vimrc loads first and even if the plugin is in start you can't call functions from it there as it is not yet loaded. You can use a AutoCmd to configure the plugin or let g:coc_user_config = ....

Please note the goal of this PR is not to have packages.packageName work like plug.plugins. The goal is to have packs work like they do when loaded from defaults dotfiles paths.

Thank you for investigating, my bad then - I assumed all plugins would be loaded already. https://github.com/neoclide/coc.nvim/wiki/Install-coc.nvim#using-vim8s-native-package-manager also does not mention anything about it 🤔

@rvolosatovs you could ask upstream about it and maybe fix their documentation than.

I think we should backport this one also to at least 20.03, but let's wait for a bit until it hits the unstable channel.

I wish this would be fixed upstream, seems like a bug to me. But at least we finally have a fix for nix, thanks @megheaiulian!