Undefined class 'FirebaseUser'

Since firebase_auth 0.18.0, the class FirebaseUser was changed to User

Starting from Version firebase_auth 0.18.0:

In the newest version of firebase_auth, the class FirebaseUser was changed to User, and the class AuthResult was changed to UserCredential. Therefore change your code to the following:

    Future<User> currentUser() async {
      final GoogleSignInAccount account = await googleSignIn.signIn();
      final GoogleSignInAuthentication authentication =
          await account.authentication;

      final GoogleAuthCredential credential = GoogleAuthProvider.credential(
          idToken: authentication.idToken,
          accessToken: authentication.accessToken);

      final UserCredential authResult =
          await _auth.signInWithCredential(credential);
      final User user = authResult.user;

      return user;
    }

---

FirebaseUser changed to User

AuthResult changed to UserCredential

GoogleAuthProvider.getCredential() changed to GoogleAuthProvider.credential()

---

onAuthStateChanged which notifies about changes to the user's sign-in state was replaced with authStateChanges()

currentUser() which is a method to retrieve the currently logged in user, was replaced with the property currentUser and it no longer returns a Future<FirebaseUser>.

Example of the above two methods:

FirebaseAuth.instance.authStateChanges().listen((event) {
   print(event.email);
});

And:

var user = FirebaseAuth.instance.currentUser;
print(user.uid);

---

Deprecation of UserUpdateInfo class for firebaseUser.updateProfile method. Example:

Future updateName(String name, FirebaseUser user) async {
  var userUpdateInfo = new UserUpdateInfo();
  userUpdateInfo.displayName = name;
  await user.updateProfile(userUpdateInfo);
  await user.reload(); 
}

now

import 'package:firebase_auth/firebase_auth.dart' as firebaseAuth;
Future updateName(String name, auth.User firebaseUser) async {
  firebaseUser.updateProfile(displayName: name);
  await firebaseUser.reload();
}

In the newest version of firebase_auth, the class FirebaseUser was changed to User, and the class AuthResult was changed to UserCredentail. Therefore change FirebaseUser to User