Incorrect type inference inside stateful loop

[bcuccioli]

TypeScript Version: 'Nightly' in playground

Search Terms: stateful loop inference any

Code

async function getPage(cursor: string | null) {
  return {
    results: <string[]>[],
    cursor: cursor + '_',
  };
}

async function paginate() {
  let cursor: string | null = null;

  while (true) {
    const page = await getPage(cursor);
    cursor = page.cursor;
  }
}

Expected behavior: No error, page type inferred specifically.

Actual behavior: 'page' implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer.(7022)

Playground Link: https://www.typescriptlang.org/play/?ts=4.0.0-dev.20200620#code/IYZwngdgxgBAZgV2gFwJYHsIwOYFNkAKweAFFAgE4joUBcMIyFqE2MAPjBAgDY8CUMAN4AoGDAr5KWUePGSQvZCHoAeRs1YBtALoA+XQBoxc8lRr0z1CjADUMAOQB9B8fEBfANwj3IkaEhYRBQMLAAHYhZgZFwSQVkYHnwYKwsGJhY2Tm4+GABeLl4ebxMAdwALVCSYEiYEXHiTcShMRhgIvHyYYFLgVGQcfCJSVIp+bzkUymsujtwAOlGJmF9fIA

Is this unexpected, or a known limitation?

[RyanCavanaugh]

This is a circularity because the return type of getPage could depend on the type of its parameter, so the loop creates a circularity: getPage(cursor) depends on cursor's possible values which depends on the type of page.cursor which depends on the type of getPage(cursor)