Got this debugging another error. Filing here for reference. Original code: https://phabricator.intern.facebook.com/P59317705
import ReactFiberLegacyContext from './ReactFiberContext';
import ReactFiberNewContext from './ReactFiberNewContext';
import {
  getUpdateExpirationTime,
  insertUpdateIntoFiber,
} from './ReactFiberUpdateQueue';
import {createCapturedValue} from './ReactCapturedValue';
import ReactFiberStack from './ReactFiberStack';
const {
  invokeGuardedCallback,
  hasCaughtError,
  clearCaughtError,
} = ReactErrorUtils;
let didWarnAboutStateTransition;
let didWarnSetStateChildContext;
let warnAboutUpdateOnUnmounted;
let warnAboutInvalidUpdates;
if (__DEV__) {
  didWarnAboutStateTransition = false;
  didWarnSetStateChildContext = false;
  const didWarnStateUpdateForUnmountedComponent = {};
  warnAboutUpdateOnUnmounted = function(fiber: Fiber) {
    const componentName = getComponentName(fiber) || 'ReactClass';
    if (didWarnStateUpdateForUnmountedComponent[componentName]) {
      return;
    }
    warning(
      false,
      'Can only update a mounted or mounting ' +
        'component. This usually means you called setState, replaceState, ' +