modules/highlights: added a wrapper around vim.fn.matchadd (#123)

* modules/highlights: added a wrapper around vim.fn.matchadd

* modules/highlights: fix mkIf

Co-authored-by: Pedro Alves <pta2002@pta2002.com>

modules/highlights.nix

@@ -15,10 +15,21 @@ with lib;
         };
       '';
     };
+
+    match = mkOption {
+      type = types.attrsOf types.str;
+      default = { };
+      description = "Define match groups";
+      example = ''
+        match = {
+          ExtraWhitespace = '\\s\\+$';
+        };
+      '';
+    };
   };
 
-  config = mkIf (config.highlight != { }) {
+  config = mkIf (config.highlight != { } || config.matches != { }) {
-    extraConfigLuaPost = ''
+    extraConfigLuaPost = (optionalString (config.highlight != { }) ''
       -- Highlight groups {{
       do
         local highlights = ${helpers.toLuaObject config.highlight}
@@ -28,6 +39,18 @@ with lib;
         end
       end
       -- }}
-    '';
+    '') ++
+    (optionalString (config.matches != { }) ''
+      -- Match groups {{
+        do
+          local match = ${helpers.toLuaObject config.match}
+
+          for k,v in pairs(match) do
+            vim.fn.matchadd(k, v)
+          end
+        end
+        -- }}
+    '');
   };
 }
+