recursiveIndexedAccessSimplification.ts(5,5): error TS4109: Type arguments for 'Array' circularly reference themselves.
recursiveIndexedAccessSimplification.ts(5,9): error TS2536: Type 'number' cannot be used to index type 'Recur<T>'.
recursiveIndexedAccessSimplification.ts(8,5): error TS2322: Type '[string, ...Recur<T>[]]' is not assignable to type 'Recur<T>'.
  Type '[string, ...Recur<T>[]]' is not assignable to type 'Recur<T>[number][]'.
    Type 'string | Recur<T>' is not assignable to type 'Recur<T>[number] & (T extends unknown[] ? {} : { [K in keyof T]?: Recur<T[K]> | undefined; })[number]'.
      Type 'string' is not assignable to type 'Recur<T>[number] & (T extends unknown[] ? {} : { [K in keyof T]?: Recur<T[K]> | undefined; })[number]'.
        Type 'string' is not assignable to type 'Recur<T>[number] & (T extends unknown[] ? {} : { [K in keyof T]?: Recur<T[K]> | undefined; })[number]'.
          Type 'string' is not assignable to type '(T extends unknown[] ? {} : { [K in keyof T]?: Recur<T[K]> | undefined; })[number]'.
recursiveIndexedAccessSimplification.ts(8,12): error TS2589: Type instantiation is excessively deep and possibly infinite.
recursiveIndexedAccessSimplification.ts(12,37): error TS2589: Type instantiation is excessively deep and possibly infinite.


==== recursiveIndexedAccessSimplification.ts (5 errors) ====
    // https://github.com/microsoft/TypeScript/issues/63270
    
    type Recur<T> =
        (T extends  (unknown[]) ? {} : { [K in keyof T]?: Recur<T[K]>}) |
        [...Recur<T>[number][]];
        ~~~~~~~~~~~~~~~~~~~~~~~
!!! error TS4109: Type arguments for 'Array' circularly reference themselves.
            ~~~~~~~~~~~~~~~~
!!! error TS2536: Type 'number' cannot be used to index type 'Recur<T>'.
    
    function join<T>(l: Recur<T>[]): Recur<T> {
        return ['marker', ...l];
        ~~~~~~
!!! error TS2322: Type '[string, ...Recur<T>[]]' is not assignable to type 'Recur<T>'.
!!! error TS2322:   Type '[string, ...Recur<T>[]]' is not assignable to type 'Recur<T>[number][]'.
!!! error TS2322:     Type 'string | Recur<T>' is not assignable to type 'Recur<T>[number] & (T extends unknown[] ? {} : { [K in keyof T]?: Recur<T[K]> | undefined; })[number]'.
!!! error TS2322:       Type 'string' is not assignable to type 'Recur<T>[number] & (T extends unknown[] ? {} : { [K in keyof T]?: Recur<T[K]> | undefined; })[number]'.
!!! error TS2322:         Type 'string' is not assignable to type 'Recur<T>[number] & (T extends unknown[] ? {} : { [K in keyof T]?: Recur<T[K]> | undefined; })[number]'.
!!! error TS2322:           Type 'string' is not assignable to type '(T extends unknown[] ? {} : { [K in keyof T]?: Recur<T[K]> | undefined; })[number]'.
               ~~~~~~~~~~~~~~~~
!!! error TS2589: Type instantiation is excessively deep and possibly infinite.
    }
    
    function a<T>(l: Recur<T>[]): void {
        const x: Recur<T> | undefined = join(l);
                                        ~~~~~~~
!!! error TS2589: Type instantiation is excessively deep and possibly infinite.
    }
    