fix: allow unit () in type_arguments

Close #140

Author: aspeddro

grammar.js

@@ -92,7 +92,8 @@ module.exports = grammar({
     [$.parameter, $._pattern],
     [$.parameter, $._parenthesized_pattern],
     [$._switch_value_pattern, $._parenthesized_pattern],
-    [$.variant_declaration]
+    [$.variant_declaration],
+    [$.unit, $._function_type_parameter_list]
   ],
 
   rules: {
@@ -290,6 +291,7 @@ module.exports = grammar({
       $.object_type,
       $.generic_type,
       $.unit_type,
+      $.unit,
       $.module_pack_type,
     ),
 

test/corpus/type_declarations.txt

@@ -307,6 +307,7 @@ Generic
 ===========================================
 
 type t<'a, 'b> = (array<'a>, array<'b>)
+type t = result<(), string>
 
 ---
 
@@ -316,7 +317,14 @@ type t<'a, 'b> = (array<'a>, array<'b>)
     (type_parameters (type_identifier) (type_identifier))
     (tuple_type
       (generic_type (type_identifier) (type_arguments (type_identifier)))
-      (generic_type (type_identifier) (type_arguments (type_identifier))))))
+      (generic_type (type_identifier) (type_arguments (type_identifier)))))
+  (type_declaration
+    (type_identifier)
+    (generic_type
+      (type_identifier)
+      (type_arguments
+        (unit)
+        (type_identifier)))))
 
 ===========================================
 Recursive