neovim: support different configuration languages (#2637)

Plugins now accept a "type" element describing the language (viml, lua
, teal, fennel, ...) in which
they are configured.

The configuration of the different plugins is aggregated per language
and made available as a key in the attribute set `programs.neovim.generatedConfigs`

For instance if you want to configure a lua package:

```
programs.neovim.plugins = [
{
plugin = packer-nvim;
type = "lua";
config = ''
    require('packer').init({
    luarocks = {
	python_cmd = 'python' -- Set the python command to use for running hererocks
    },
    })
'';
}
]
```
and you can save the generated lua config to a file via

```
  xdg.configFile = {
    "nvim/init.generated.lua".text = config.programs.neovim.generatedConfigs.lua;
  };
```

modules/programs/neovim.nix

@@ -20,10 +20,19 @@ let
     options = {
       config = mkOption {
         type = types.lines;
-        description = "vimscript for this plugin to be placed in init.vim";
+        description =
+          "Script to configure this plugin. The scripting language should match type.";
         default = "";
       };
 
+      type = mkOption {
+        type =
+          types.either (types.enum [ "lua" "viml" "teal" "fennel" ]) types.str;
+        description =
+          "Language used in config. Configurations are aggregated per-language.";
+        default = "viml";
+      };
+
       optional = mkEnableOption "optional" // {
         description = "Don't load by default (load with :packadd)";
       };
@@ -141,6 +150,28 @@ in {
         '';
       };
 
+      generatedConfigs = mkOption {
+        type = types.attrsOf types.lines;
+        visible = true;
+        readOnly = true;
+        example = literalExpression ''
+          {
+            viml = '''
+              " Generated by home-manager
+              set packpath^=/nix/store/cn8vvv4ymxjf8cfzg7db15b2838nqqib-vim-pack-dir
+              set runtimepath^=/nix/store/cn8vvv4ymxjf8cfzg7db15b2838nqqib-vim-pack-dir
+            ''';
+
+            lua = '''
+              -- Generated by home-manager
+              vim.opt.background = "dark"
+            ''';
+          }'';
+        description = ''
+          Generated configurations with as key their language (set via type).
+        '';
+      };
+
       package = mkOption {
         type = types.package;
         default = pkgs.neovim-unwrapped;
@@ -270,12 +301,25 @@ in {
   };
 
   config = let
+    # transform all plugins into an attrset
+    pluginsNormalized = map (x:
+      if (x ? plugin) then
+        x
+      else {
+        type = x.type or "viml";
+        plugin = x;
+        config = "";
+        optional = false;
+      }) cfg.plugins;
+    suppressNotVimlConfig = p:
+      if p.type != "viml" then p // { config = ""; } else p;
+
     neovimConfig = pkgs.neovimUtils.makeNeovimConfig {
       inherit (cfg)
         extraPython3Packages withPython3 withNodeJs withRuby viAlias vimAlias;
       configure = cfg.configure // moduleConfigure;
-      plugins = cfg.plugins
-        ++ optionals cfg.coc.enable [ pkgs.vimPlugins.coc-nvim ];
+      plugins = (map suppressNotVimlConfig pluginsNormalized)
+        ++ optionals cfg.coc.enable [{ plugin = pkgs.vimPlugins.coc-nvim; }];
       customRC = cfg.extraConfig;
     };
 
@@ -291,6 +335,12 @@ in {
 
     programs.neovim.generatedConfigViml = neovimConfig.neovimRcContent;
 
+    programs.neovim.generatedConfigs = let
+      grouped = lib.lists.groupBy (x: x.type) pluginsNormalized;
+      concatConfigs =
+        lib.concatMapStrings (p: builtins.trace p.plugin.name p.config);
+    in mapAttrs (name: vals: concatConfigs vals) grouped;
+
     home.packages = [ cfg.finalPackage ];
 
     xdg.configFile."nvim/init.vim" = mkIf (neovimConfig.neovimRcContent != "") {