fixed "TS2589: Type instantiation is excessively deep and possibly infinite." error on alternation

Author: codpro2005

src/index.ts

@@ -243,13 +243,16 @@ type FlattenGroupsDeep<TGroups extends Groups> = unknown extends AsLinked<TGroup
  >]
  : []
 ;
-type FlattenTokenDeep<TToken extends Token> = TToken extends { type: 'alternation' } ? [
- ...FlattenTokenDeep<TToken['left']>,
- ...FlattenTokenDeep<TToken['right']>
-] : TToken extends { type: 'groups' }
- ? FlattenGroupsDeep<TToken['groups']>
+type FlattenTokenDeepInternal<TToken extends Token, Limit extends unknown[]> = Limit extends [unknown, ...infer L]
+ ? TToken extends { type: 'alternation' } ? [
+ ...FlattenTokenDeepInternal<TToken['left'], L>,
+ ...FlattenTokenDeepInternal<TToken['right'], L>
+ ] : TToken extends { type: 'groups' }
+ ? FlattenGroupsDeep<TToken['groups']>
+ : never
  : never
 ;
+type FlattenTokenDeep<TToken extends Token> = FlattenTokenDeepInternal<TToken, Range<20>>;
 // DFS
 type IndexifyGroupsDeep<TGroups extends Groups, TIndex extends number> = unknown extends AsLinked<TGroups, infer First, infer Rest>
  ? [
@@ -270,7 +273,6 @@ type IndexifyTokenDeepInternal<TToken extends Token, TIndex extends number> = TT
  left: IndexifyTokenDeepInternal<TToken['left'], TIndex>,
  right: IndexifyTokenDeepInternal<TToken['right'], Add<
  TIndex,
- // @ts-expect-error: this should terminate
  FlattenTokenDeep<TToken['left']>['length'] 
  & number
  >>