Function warnOnInvalidKey

docs/external/js/react-dom.development.js:13909–13943

* Warns if there is a duplicate or missing key

(child, knownKeys)

    function warnOnInvalidKey(child, knownKeys) {
      {
        if (typeof child !== 'object' || child === null) {
          return knownKeys;
        }

        switch (child.$$typeof) {
          case REACT_ELEMENT_TYPE:
          case REACT_PORTAL_TYPE:
            warnForMissingKey(child);
            var key = child.key;

            if (typeof key !== 'string') {
              break;
            }

            if (knownKeys === null) {
              knownKeys = new Set();
              knownKeys.add(key);
              break;
            }

            if (!knownKeys.has(key)) {
              knownKeys.add(key);
              break;
            }

            error('Encountered two children with the same key, `%s`. ' + 'Keys should be unique so that components maintain their identity ' + 'across updates. Non-unique keys may cause children to be ' + 'duplicated and/or omitted — the behavior is unsupported and ' + 'could change in a future version.', key);

            break;
        }
      }

      return knownKeys;
    }

    function reconcileChildrenArray(returnFiber, currentFirstChild, newChildren, expirationTime) {
      // This algorithm can't optimize by searching from both ends since we