autoUpgradeAnonymousUsers onUpgrade event not invoked if merge is required.

[mcroker]

[REQUIRED] Describe your environment

• Operating System version: MacOs Tahoe 26.3.1 (a) (25D771280a)
• Browser version: Chrome Version 147.0.7727.138 (Official Build) (x86_64)
• Firebase UI version: "@firebase-oss/ui-angular": "^7.0.2-beta"
• AngularFire Version: "@angular/fire": "~20.0.1",
• Firebase SDK version: "firebase": "~11.10.0"
• Package name: firebase-oss/ui-angular/auth

[REQUIRED] Describe the problem

I am using these two behaviours together autoAnonymousLogin, autoUpgradeAnonymousUsers.

The application behaviour I want is that users is initially signed anonymous credentials, and when they attempt to write to the database they are directed to firebase-ui to log-in using googleProvider and their credentials are upgraded to non-anonymous (i.e. the oauth credential is linked to the existing account).

If credential linking succeeds this works perfectly - the account is merged and the onUpgrade() handler is called.

If credential linking does not succeed, such as when the oAuth credential is already mapped to the anonymous credential:

• an error is presented in the UI An account already exists with this email. Please sign in with that account.
• The onUpgrade() handler is not called.

I can find no way to intercept this to execute my logic to merge the accounts. I believe the onUpgrade() handler should be called, but as best I can tell linkWithCredential() throws an exception which prevents the execution of the onUpgrade() handler.

firebaseui-web/packages/core/src/behaviors/anonymous-upgrade.ts

Line 36 in 3bbe28a

const result = await linkWithCredential(currentUser, credential);

Steps to reproduce

Create a firebase project with googleAuthentiaion provider enabled (any oAuth provider should work)
In angular project, with angularfire, using behaviours autoAnonymousLogin, autoUpgradeAnonymousUsers.

Create an anonymous user
Link that user to a google credential
Log out, and create a new anonymous users
Attempt to link that user to the same google credential

The linkWithCredential() call will fail (correct behavior), but onUpgrade() will not fire (I think this is unexpected).

[mcroker]

Possibly related to #1038

[mcroker]

The only way I could find to work-around this was to create my own google-sign-in component... the logic to handle upgrading unauthenticated accounts is as below... (uses linkWithCredential rather than linkWithPopup).

async handleOAuthSignIn() {
    const currentUser = this.auth.currentUser;

    const result = await signInWithPopup(this.auth, this.googleProvider);
    const credential = GoogleAuthProvider.credentialFromResult(result);

    if (currentUser !== null && credential !== null) {
      try {
        if (currentUser?.isAnonymous) {
          // Attempt to link to the currently logged-in account
          await linkWithCredential(currentUser, credential);
          console.log("Account linked successfully!");
        }
      } catch (error: any) {
        // Handle the 'Already in Use' error
        if (error.code === 'auth/credential-already-in-use') {
          console.warn("This Google account is linked to another user. Starting merge...");
          await handleMerge(this.auth, credential);
        } else {
          console.error("Link failed:", error.message);
          handleFirebaseError(this.ui(), error);
        }
      }
    }
  }

async function handleMerge(auth: Auth, credential: OAuthCredential) {
          
          // Do something as old user

          console.log('signing in as new user');
          await signInWithCredential(this.auth, credential);

          // Do something as new user

}        

[russellwheatley]

Hey @mcroker - thank you for raising this issue. I'll open a PR to resolve this, there really should be a way to handle unhappy path when linking accounts.

[mcroker]

Thanks Russell - love the speed of response.