SwiftでfirebaseAuthを利用したgoogleログインを実装したいです。

公式通りにコード記述しているのにエラーが出てしまいます。

LoginViewController.Swift

//
//  LoginViewController.swift
//  Shindan
//
//  Created by  on 2021/03/04.
//

import UIKit
import Firebase
import GoogleSignIn

class LoginViewController: UIViewController {
    
    @IBOutlet weak var signInButton: GIDSignInButton!
    
    
    override func viewDidLoad() {
        super.viewDidLoad()
        GIDSignIn.sharedInstance()?.presentingViewController = self
        GIDSignIn.sharedInstance().signIn()
    }
    
    func sign(_ signIn: GIDSignIn!, didSignInFor user: GIDGoogleUser!, withError error: Error?) {
      // ...
      if let error = error {
        // ...
        return
      }

      guard let authentication = user.authentication else { return }
      let credential = GoogleAuthProvider.credential(withIDToken: authentication.idToken,
                                                        accessToken: authentication.accessToken)
      // ...
    }
    
    Auth.auth().signIn(with: credential) { (authResult, error) in
      if let error = error {
        let authError = error as NSError
        if (isMFAEnabled && authError.code == AuthErrorCode.secondFactorRequired.rawValue) {
          // The user is a multi-factor user. Second factor challenge is required.
          let resolver = authError.userInfo[AuthErrorUserInfoMultiFactorResolverKey] as! MultiFactorResolver
          var displayNameString = ""
          for tmpFactorInfo in (resolver.hints) {
            displayNameString += tmpFactorInfo.displayName ?? ""
            displayNameString += " "
          }
          self.showTextInputPrompt(withMessage: "Select factor to sign in\n(displayNameString)", completionBlock: { userPressedOK, displayName in
            var selectedHint: PhoneMultiFactorInfo?
            for tmpFactorInfo in resolver.hints {
              if (displayName == tmpFactorInfo.displayName) {
                selectedHint = tmpFactorInfo as? PhoneMultiFactorInfo
              }
            }
            PhoneAuthProvider.provider().verifyPhoneNumber(with: selectedHint!, uiDelegate: nil, multiFactorSession: resolver.session) { verificationID, error in
              if error != nil {
                print("Multi factor start sign in failed. Error: (error.debugDescription)")
              } else {
                self.showTextInputPrompt(withMessage: "Verification code for (selectedHint?.displayName ?? "")", completionBlock: { userPressedOK, verificationCode in
                  let credential: PhoneAuthCredential? = PhoneAuthProvider.provider().credential(withVerificationID: verificationID!, verificationCode: verificationCode!)
                  let assertion: MultiFactorAssertion? = PhoneMultiFactorGenerator.assertion(with: credential!)
                  resolver.resolveSignIn(with: assertion!) { authResult, error in
                    if error != nil {
                      print("Multi factor finanlize sign in failed. Error: (error.debugDescription)")
                    } else {
                      self.navigationController?.popViewController(animated: true)
                    }
                  }
                })
              }
            }
          })
        } else {
          self.showMessagePrompt(error.localizedDescription)
          return
        }
        // ...
        return
      }
      // User is signed in
      // ...
    }
    
    let firebaseAuth = Auth.auth()
    do {
    try firebaseAuth.signOut()
    } catch let signOutError as NSError {
    print ("Error signing out: %@", signOutError)
    }
  
    /*
    // MARK: - Navigation

    // In a storyboard-based application, you will often want to do a little preparation before navigation
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        // Get the new view controller using segue.destination.
        // Pass the selected object to the new view controller.
    }
    */

}

エラー内容
Class 'LoginViewController' has no initializers

In declaration of 'LoginViewController'

Auth.auth()
Consecutive declarations on a line must be separated by ';'
Insert ';'
Expected '(' in argument list of function declaration
Expected '{' in body of function declaration
Expected 'func' keyword in instance method declaration
Insert 'func '
Expected declaration

let firebaseAuth = Auth.auth()
Use of 'Auth' refers to instance method rather than class 'Auth' in module 'FirebaseAuth'
Use 'FirebaseAuth.' to reference the class in module 'FirebaseAuth'

catch let signOutError as NSError
Consecutive declarations on a line must be separated by ';'
Insert ';'
Expected declaration
Type annotation missing in pattern

AppDelegate.swift

//
//  AppDelegate.swift
//  Shindan
//
//  Created by  on 2021/03/03.
//

import UIKit
import Firebase
import GoogleSignIn

@main
class AppDelegate: UIResponder, UIApplicationDelegate, GIDSignInDelegate {


    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        
        // Use Firebase library to configure APIs
        FirebaseApp.configure()

        GIDSignIn.sharedInstance().clientID = FirebaseApp.app()?.options.clientID
        GIDSignIn.sharedInstance().delegate = self
            return true
    }
    
    @available(iOS 9.0, *)
    func application(_ application: UIApplication, open url: URL, options: [UIApplication.OpenURLOptionsKey : Any])
      -> Bool {
      return GIDSignIn.sharedInstance().handle(url)
    }
    
    func sign(_ signIn: GIDSignIn!, didSignInFor user: GIDGoogleUser!, withError error: Error?) {
      // ...
      if let error = error {
        // ...
        return
      }

      guard let authentication = user.authentication else { return }
      let credential = GoogleAuthProvider.credential(withIDToken: authentication.idToken,
                                                        accessToken: authentication.accessToken)
      // ...
    }


    func sign(_ signIn: GIDSignIn!, didDisconnectWith user: GIDGoogleUser!, withError error: Error!) {
        // Perform any operations when the user disconnects from app here.
        // ...
    }
    // MARK: UISceneSession Lifecycle

    func application(_ application: UIApplication, configurationForConnecting connectingSceneSession: UISceneSession, options: UIScene.ConnectionOptions) -> UISceneConfiguration {
        // Called when a new scene session is being created.
        // Use this method to select a configuration to create the new scene with.
        return UISceneConfiguration(name: "Default Configuration", sessionRole: connectingSceneSession.role)
    }

    func application(_ application: UIApplication, didDiscardSceneSessions sceneSessions: Set<UISceneSession>) {
        // Called when the user discards a scene session.
        // If any sessions were discarded while the application was not running, this will be called shortly after application:didFinishLaunchingWithOptions.
        // Use this method to release any resources that were specific to the discarded scenes, as they will not return.
    }


}

参考サイト

なぜエラーが出るのかわかりません。
回答お願いします。

Fixができるものもしていますが、エラーが追加されるだけでした。