neovim: simplify plugin config schema

hosts/common/programs/neovim/default.nix

@@ -3,11 +3,21 @@ moduleArgs@{ config, lib, pkgs, ... }:
 let
   inherit (builtins) map;
   inherit (lib) concatMapStrings mkIf optionalString;
-  # this structure roughly mirrors home-manager's `programs.neovim.plugins` option
   plugins = import ./plugins.nix moduleArgs;
   plugin-packages = map (p: p.plugin) plugins;
-  plugin-config-viml = concatMapStrings (p: optionalString (p.type or "" == "viml") p.config) plugins;
-  plugin-config-lua = concatMapStrings (p: optionalString (p.type or "" == "lua") p.config) plugins;
+  plugin-configs = concatMapStrings (p:
+    optionalString
+      (p ? config) (
+        if (p.type or "") == "viml" then
+          p.config
+        else
+          ''
+            lua <<EOF
+            ${p.config}
+            EOF
+          ''
+      )
+  ) plugins;
 in
 {
   sane.programs.neovim = {
@@ -36,13 +46,8 @@ in
         customRC = ''
           ${builtins.readFile ./vimrc}
 
-          """"" PLUGIN CONFIG (vim)
-          ${plugin-config-viml}
-
-          """"" PLUGIN CONFIG (lua)
-          lua <<EOF
-          ${plugin-config-lua}
-          EOF
+          """"" PLUGIN CONFIG
+          ${plugin-configs}
         '';
       };
       neovim-unwrapped' = with pkgs; (neovim-unwrapped.override {