finalizeTree method Null safety

Implementation

@pragma('vm:notify-debugger-on-exception')
void finalizeTree() {
  if (!kReleaseMode) {
    Timeline.startSync('FINALIZE TREE');
  }
  try {
    lockState(_inactiveElements._unmountAll); // this unregisters the GlobalKeys
    assert(() {
      try {
        _debugVerifyGlobalKeyReservation();
        _debugVerifyIllFatedPopulation();
        if (_debugElementsThatWillNeedToBeRebuiltDueToGlobalKeyShenanigans != null &&
            _debugElementsThatWillNeedToBeRebuiltDueToGlobalKeyShenanigans!.isNotEmpty) {
          final Set<GlobalKey> keys = HashSet<GlobalKey>();
          for (final Element element in _debugElementsThatWillNeedToBeRebuiltDueToGlobalKeyShenanigans!.keys) {
            if (element._lifecycleState != _ElementLifecycle.defunct) {
              keys.addAll(_debugElementsThatWillNeedToBeRebuiltDueToGlobalKeyShenanigans![element]!);
            }
          }
          if (keys.isNotEmpty) {
            final Map<String, int> keyStringCount = HashMap<String, int>();
            for (final String key in keys.map<String>((GlobalKey key) => key.toString())) {
              if (keyStringCount.containsKey(key)) {
                keyStringCount.update(key, (int value) => value + 1);
              } else {
                keyStringCount[key] = 1;
              }
            }
            final List<String> keyLabels = <String>[];
            keyStringCount.forEach((String key, int count) {
              if (count == 1) {
                keyLabels.add(key);
              } else {
                keyLabels.add('$key ($count different affected keys had this toString representation)');
              }
            });
            final Iterable<Element> elements = _debugElementsThatWillNeedToBeRebuiltDueToGlobalKeyShenanigans!.keys;
            final Map<String, int> elementStringCount = HashMap<String, int>();
            for (final String element in elements.map<String>((Element element) => element.toString())) {
              if (elementStringCount.containsKey(element)) {
                elementStringCount.update(element, (int value) => value + 1);
              } else {
                elementStringCount[element] = 1;
              }
            }
            final List<String> elementLabels = <String>[];
            elementStringCount.forEach((String element, int count) {
              if (count == 1) {
                elementLabels.add(element);
              } else {
                elementLabels.add('$element ($count different affected elements had this toString representation)');
              }
            });
            assert(keyLabels.isNotEmpty);
            final String the = keys.length == 1 ? ' the' : '';
            final String s = keys.length == 1 ? '' : 's';
            final String were = keys.length == 1 ? 'was' : 'were';
            final String their = keys.length == 1 ? 'its' : 'their';
            final String respective = elementLabels.length == 1 ? '' : ' respective';
            final String those = keys.length == 1 ? 'that' : 'those';
            final String s2 = elementLabels.length == 1 ? '' : 's';
            final String those2 = elementLabels.length == 1 ? 'that' : 'those';
            final String they = elementLabels.length == 1 ? 'it' : 'they';
            final String think = elementLabels.length == 1 ? 'thinks' : 'think';
            final String are = elementLabels.length == 1 ? 'is' : 'are';
            // TODO(jacobr): make this error more structured to better expose which widgets had problems.
            throw FlutterError.fromParts(<DiagnosticsNode>[
              ErrorSummary('Duplicate GlobalKey$s detected in widget tree.'),
              // TODO(jacobr): refactor this code so the elements are clickable
              // in GUI debug tools.
              ErrorDescription(
                'The following GlobalKey$s $were specified multiple times in the widget tree. This will lead to '
                'parts of the widget tree being truncated unexpectedly, because the second time a key is seen, '
                'the previous instance is moved to the new location. The key$s $were:\n'
                '- ${keyLabels.join("\n  ")}\n'
                'This was determined by noticing that after$the widget$s with the above global key$s $were moved '
                'out of $their$respective previous parent$s2, $those2 previous parent$s2 never updated during this frame, meaning '
                'that $they either did not update at all or updated before the widget$s $were moved, in either case '
                'implying that $they still $think that $they should have a child with $those global key$s.\n'
                'The specific parent$s2 that did not update after having one or more children forcibly removed '
                'due to GlobalKey reparenting $are:\n'
                '- ${elementLabels.join("\n  ")}'
                '\nA GlobalKey can only be specified on one widget at a time in the widget tree.',
              ),
            ]);
          }
        }
      } finally {
        _debugElementsThatWillNeedToBeRebuiltDueToGlobalKeyShenanigans?.clear();
      }
      return true;
    }());
  } catch (e, stack) {
    // Catching the exception directly to avoid activating the ErrorWidget.
    // Since the tree is in a broken state, adding the ErrorWidget would
    // cause more exceptions.
    _debugReportException(ErrorSummary('while finalizing the widget tree'), e, stack);
  } finally {
    if (!kReleaseMode) {
      Timeline.finishSync();
    }
  }
}