add an external scanner for arrow shorthand, basically just looksahead to avoid '{', this seems to solve ()=>{}() being treated as legal

Author: jackschu

grammar.js

@@ -15,6 +15,7 @@ module.exports = grammar({
     $._automatic_semicolon,
     $._template_chars,
     $._ternary_qmark,
+    $._shorthand_arrow,
     $.html_comment,
     '||',
     // We use escape sequence and regex pattern to tell the scanner if we're currently inside a string or template string, in which case
@@ -769,11 +770,10 @@ module.exports = grammar({
         )),
         $._call_signature,
       ),
-      '=>',
-      field('body', choice(
-        $.expression,
-        $.statement_block,
-      )),
+      choice(
+          seq($._shorthand_arrow, field('body', $.expression)),
+          seq(choice('=>', $._shorthand_arrow), field('body', $.statement_block,)),
+      ),
     ),
 
     // Override