Function validateIterable

packages/react-server/src/ReactFizzServer.js:3182–3228

(
  task: Task,
  iterable: Iterable<any>,
  childIndex: number,
  iterator: Iterator<any>,
  iteratorFn: () => ?Iterator<any>,
)

}

function validateIterable(
  task: Task,
  iterable: Iterable<any>,
  childIndex: number,
  iterator: Iterator<any>,
  iteratorFn: () => ?Iterator<any>,
): void {
  if (__DEV__) {
    if (iterator === iterable) {
      // We don't support rendering Generators as props because it's a mutation.
      // See https://github.com/facebook/react/issues/12995
      // We do support generators if they were created by a GeneratorFunction component
      // as its direct child since we can recreate those by rerendering the component
      // as needed.
      const isGeneratorComponent =
        childIndex === -1 && // Only the root child is valid
        task.componentStack !== null &&
        typeof task.componentStack.type === 'function' && // FunctionComponent
        // $FlowFixMe[method-unbinding]
        Object.prototype.toString.call(task.componentStack.type) ===
          '[object GeneratorFunction]' &&
        // $FlowFixMe[method-unbinding]
        Object.prototype.toString.call(iterator) === '[object Generator]';
      if (!isGeneratorComponent) {
        if (!didWarnAboutGenerators) {
          console.error(
            'Using Iterators as children is unsupported and will likely yield ' +
              'unexpected results because enumerating a generator mutates it. ' +
              'You may convert it to an array with `Array.from()` or the ' +
              '`[...spread]` operator before rendering. You can also use an ' +
              'Iterable that can iterate multiple times over the same items.',
          );
        }
        didWarnAboutGenerators = true;
      }
    } else if ((iterable: any).entries === iteratorFn) {
      // Warn about using Maps as children
      if (!didWarnAboutMaps) {
        console.error(
          'Using Maps as children is not supported. ' +
            'Use an array of keyed ReactElements instead.',
        );
        didWarnAboutMaps = true;
      }
    }
  }
}

function validateAsyncIterable(
  task: Task,