Add supertypes

grammar.js

@@ -47,6 +47,12 @@ module.exports = grammar({
     /\\?\s/,
   ],
 
+  supertypes: $ => [
+    $._statement,
+    $._expression,
+    $._primary_expression,
+  ],
+
   word: $ => $.word,
 
   rules: {

src/grammar.json

@@ -2505,6 +2505,10 @@
     "_simple_variable_name",
     "_special_variable_name"
   ],
-  "supertypes": []
+  "supertypes": [
+    "_statement",
+    "_expression",
+    "_primary_expression"
+  ]
 }