The argument type 'Map<String, dynamic> Function()' can't be assigned to the parameter type 'Map<String, dynamic>'

Try the following:

  Record.fromSnapshot(DocumentSnapshot snapshot)
      : this.fromMap(snapshot.data(), reference: snapshot.reference);

data() is a method:

  /// Contains all the data of this [DocumentSnapshot].
  Map<String, dynamic> data() {
    return _CodecUtility.replaceDelegatesWithValueInMap(
        _delegate.data(), _firestore);
  }

that returns a Map<String, dynamic>

It's because DocumentSnapshot.data() is a function that returns Map<String, dynamic>.

So, the answer is:

  Record.fromSnapshot(DocumentSnapshot snapshot)
      : this.fromMap(snapshot.data(), reference: snapshot.reference);