anchor.diff:      var controller =
           StreamController<T>(sync: true, onCancel: _completer._cancel);
   
  -    value.then((value) {
  +    _completer._inner?.future.then((value) {
         controller.add(value);
         controller.close();
       }, onError: (Object error, StackTrace stackTrace) {
  
positive.code:   /// If [complete] was called with a [Future] argument, this completer may be
    /// completed before it's [operation] is completed. In that case the
    /// [operation] may still be canceled before the result is available.
    bool get isCompleted => _isCompleted;
  
    /// Whether the completer was canceled before the result was ready.
    bool get isCanceled => _isCanceled;
  
negative.code:   /// The [onCancel] function will be called at most once.
    CancelableCompleter({FutureOr Function()? onCancel}) : _onCancel = onCancel;
  
    /// Whether the [_inner] completer has been completed.
    ///
    /// At this point it's no longer possible to cancel the operation.
    bool get _isCompleted => _cancelCompleter == null;
  
    /// Whether the completer was canceled before the result was ready.
    ///
    /// At this point, it's no longer possible to complete the operation.
    bool get _isCanceled => _inner == null;
  
    /// Whether the [complete] or [completeError] have been called.
    ///
    /// Once this completer has been completed with either a result or error,
  