Promote metavariable out of _non_special_token

Allows deduplicating _common_token and _non_special_token

Author: ninevra

grammar.js

@@ -150,6 +150,7 @@ module.exports = grammar({
       $.token_tree_pattern,
       $.token_repetition_pattern,
       $.token_binding_pattern,
+      $.metavariable,
       $._non_special_token
     ),
 
@@ -177,6 +178,7 @@ module.exports = grammar({
     _tokens: $ => choice(
       $.token_tree,
       $.token_repetition,
+      $.metavariable,
       $._non_special_token
     ),
 
@@ -190,12 +192,10 @@ module.exports = grammar({
       '$', '(', repeat($._tokens), ')', optional(/[^+*?]+/), choice('+', '*', '?')
     ),
 
+    // Matches non-delimiter tokens common to both macro invocations and
+    // definitions. This is everything except $ and metavariables (which begin
+    // with $).
     _non_special_token: $ => choice(
-      $._never_special_token,
-      $.metavariable
-    ),
-
-    _never_special_token: $ => choice(
       $._literal, $.identifier, $.mutable_specifier, $.self, $.super, $.crate,
       alias(choice(...primitive_types), $.primitive_type),
       /[/_\-=->,;:::!=?.@*&#%^+<>|~]+/,
@@ -910,8 +910,9 @@ module.exports = grammar({
       alias($.delim_token_tree, $.token_tree),
     ),
 
+    // Should match any token other than a delimiter.
     _non_delim_token: $ => choice(
-      $._never_special_token,
+      $._non_special_token,
       '$'
     ),
 

src/grammar.json

@@ -308,6 +308,10 @@
           "type": "SYMBOL",
           "name": "token_binding_pattern"
         },
+        {
+          "type": "SYMBOL",
+          "name": "metavariable"
+        },
         {
           "type": "SYMBOL",
           "name": "_non_special_token"
@@ -529,6 +533,10 @@
           "type": "SYMBOL",
           "name": "token_repetition"
         },
+        {
+          "type": "SYMBOL",
+          "name": "metavariable"
+        },
         {
           "type": "SYMBOL",
           "name": "_non_special_token"
@@ -654,19 +662,6 @@
       ]
     },
     "_non_special_token": {
-      "type": "CHOICE",
-      "members": [
-        {
-          "type": "SYMBOL",
-          "name": "_never_special_token"
-        },
-        {
-          "type": "SYMBOL",
-          "name": "metavariable"
-        }
-      ]
-    },
-    "_never_special_token": {
       "type": "CHOICE",
       "members": [
         {
@@ -5035,7 +5030,7 @@
       "members": [
         {
           "type": "SYMBOL",
-          "name": "_never_special_token"
+          "name": "_non_special_token"
         },
         {
           "type": "STRING",