Improve index syntax

tree-sitter-dust/corpus/index.txt

@@ -90,3 +90,25 @@ Nested Indexes
         (expression
           (value
             (integer)))))))
+
+================================================================================
+Function Call Index
+================================================================================
+
+x:(y):0
+
+--------------------------------------------------------------------------------
+
+(root
+  (statement
+    (expression
+      (index
+        (expression
+          (index
+            (expression
+              (identifier))
+            (expression
+              (function_call))))
+        (expression
+          (value
+            (integer)))))))

tree-sitter-dust/grammar.js

@@ -114,19 +114,13 @@ module.exports = grammar({
     index: $ => prec.left(seq(
       $.expression,
       ':',
-      $._index_expression,
+      $.expression,
       optional(seq(
         '..',
-        $._index_expression,
+        $.expression,
       )),
     )),
 
-    _index_expression: $ => prec(1,choice(
-      $.integer,
-      $.identifier,
-      $.function_call,
-    )),
-
     math: $ => prec.left(seq(
       $.expression,
       $.math_operator,      
@@ -298,10 +292,12 @@ module.exports = grammar({
       field('body', $.block),
     ),
 
-    function_call: $ => choice(
+    function_call: $ => prec.right(choice(
+      '(',
       $.built_in_function,
       $._context_defined_function,
-    ),
+      ')',
+    )),
 
     _context_defined_function: $ => prec.right(seq(
       $.identifier,

tree-sitter-dust/src/grammar.json

@@ -1233,17 +1233,29 @@
       ]
     },
     "function_call": {
-      "type": "CHOICE",
-      "members": [
-        {
-          "type": "SYMBOL",
-          "name": "built_in_function"
-        },
-        {
-          "type": "SYMBOL",
-          "name": "_context_defined_function"
-        }
-      ]
+      "type": "PREC_RIGHT",
+      "value": 0,
+      "content": {
+        "type": "CHOICE",
+        "members": [
+          {
+            "type": "STRING",
+            "value": "("
+          },
+          {
+            "type": "SYMBOL",
+            "name": "built_in_function"
+          },
+          {
+            "type": "SYMBOL",
+            "name": "_context_defined_function"
+          },
+          {
+            "type": "STRING",
+            "value": ")"
+          }
+        ]
+      }
     },
     "_context_defined_function": {
       "type": "PREC_RIGHT",

tree-sitter-dust/src/node-types.json

@@ -255,7 +255,7 @@
     "fields": {},
     "children": {
       "multiple": true,
-      "required": true,
+      "required": false,
       "types": [
         {
           "type": "built_in_function",