Function validateExplicitKey

code/new-context-api/public/app.js:18822–18848

* Warn if the element doesn't have an explicit key assigned to it. * This element is in an array. The array could grow and shrink or be * reordered. All children that haven't already been validated are required to * have a "key" property assigned to it. Error statuses are cached so a warning * w

(element, parentType)

 * @param {*} parentType element's parent's type.
 */
function validateExplicitKey(element, parentType) {
  if (!element._store || element._store.validated || element.key != null) {
    return;
  }
  element._store.validated = true;

  var currentComponentErrorInfo = getCurrentComponentErrorInfo(parentType);
  if (ownerHasKeyUseWarning[currentComponentErrorInfo]) {
    return;
  }
  ownerHasKeyUseWarning[currentComponentErrorInfo] = true;

  // Usually the current owner is the offender, but if it accepts children as a
  // property, it may be the creator of the child that's responsible for
  // assigning it a key.
  var childOwner = '';
  if (element && element._owner && element._owner !== ReactCurrentOwner.current) {
    // Give the component that originally created this child.
    childOwner = ' It was passed a child from ' + getComponentName(element._owner) + '.';
  }

  currentlyValidatingElement = element;
  {
    warning(false, 'Each child in an array or iterator should have a unique "key" prop.' + '%s%s See https://fb.me/react-warning-keys for more information.%s', currentComponentErrorInfo, childOwner, getStackAddendum());
  }
  currentlyValidatingElement = null;
}

/**
 * Ensure that every element either is passed in a static location, in an