(Edit: filed #10518 for this. Added FlowFixMe for existing issue for now.)

(Edit 2: rebased on master where this is fixed)

I almost fixed Flow after replacing ReactInstanceType with Fiber but this code puzzles me:

// TODO (bvaughn) Rename the findNodeHandle module to something more descriptive
// eg findInternalHostInstance. This will reduce the likelihood of someone
// accidentally deep-requiring this version.
function findNodeHandle(componentOrHandle: any): any {
  if (__DEV__) {
    // TODO: fix this unsafe cast to work with Fiber.
    var owner = ((ReactCurrentOwner.current: any): Fiber | null);
    if (owner !== null) {
      warning(
        owner._warnedAboutRefsInRender,
        '%s is accessing findNodeHandle inside its render(). ' +
          'render() should be a pure function of props and state. It should ' +
          'never access something that requires stale data from the previous ' +
          'render, such as refs. Move this logic to componentDidMount and ' +
          'componentDidUpdate instead.',
        getComponentName(owner) || 'A component',
      );

      owner._warnedAboutRefsInRender = true;
    }
  }

In my understanding if we actually go down that code path in Fiber, we'll throw because we can't define _warnedAboutRefsInRender on a Fiber (it's non-extensible). Equivalent code in findDOMNode makes sure to put it on the stateNode but that doesn't seem to be the case here.

So is it a bug? Does the warning unintentionally throw?

⚛️🎉

I'm stacking every fiber in my body in favor of this PR.

I think this is ready for review.

Bundle diff: https://gist.github.com/gaearon/2d67d4fa6c77509dfc6760251d119574

Hi, I want to know how to find the complete src code(because maybe I want to learn Stack reconciler) after we delete Stack reconciler?

You can always view old release tags on GitHub or check out old branches like 15-stable in git.

Thanks, I forget that. So will we update Stack reconciler on old branches like 15-stable in the future?

No, there are no plans to work on Stack. Fiber replaces it.

Rebased.

Split into four parts.

Safe to land now:
#10794
#10796

Worth testing internally:
#10797
#10798