let children: string | A[] = []
while (typeof children !== 'string') {
    const index = children.length - 1
    children = children[index].children
interface A {
  children: A[] | string
🙁 Actual behavior
'index' implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer
🙂 Expected behavior
No error here
          
Duplicate of #43047. The type of index depends on the type of children, the type of children depends on the type of index (due to the reassignment).
Just add a type annotation.