fix: apply username from backend instead of guessing

lib/Controller/UsersController.php

@@ -173,6 +173,7 @@ public function create(string $email, string $displayName, string $language, arr
 				'message' => $this->l10n->t(
 					'User successfully created'
 				),
+				'username' => $username,
 			],
 			Http::STATUS_CREATED
 		);

src/views/GuestForm.vue

@@ -171,15 +171,7 @@ export default {
 
 	watch: {
 		'guest.email': function() {
-			if (this.guest.email) {
-				this.guest.username = this.guest.email
-			} else {
-				this.guest.username = ''
-			}
-
-			this.$nextTick(() => {
-				this.resetErrors()
-			})
+			this.resetErrors()
 		},
 	},
 
@@ -233,13 +225,16 @@ export default {
 
 			this.loading = true
 			try {
-				await axios.put(generateOcsUrl('/apps/guests/api/v1/users'), {
+				const { data } = await axios.put(generateOcsUrl('/apps/guests/api/v1/users'), {
 					displayName: this.guest.fullName,
 					email: this.guest.email,
 					language: this.guest.language,
 					groups: this.guest.groups,
 				})
 
+				// ensure the username is set - we do not know it in advance as it is generated by the backend
+				this.guest.username = data.ocs.data.username
+
 				if (this.integrationApp === 'files') {
 					await this.setupGuestShare()
 					return

tests/unit/Controller/UsersControllerTest.php

@@ -707,7 +707,10 @@ public function testCreateSuccessWithGroupsAsSubadmin(): void {
 
 		$response = $this->controller->create('new@example.com', 'Test User', 'en', ['group1', 'group2']);
 		$this->assertEquals(Http::STATUS_CREATED, $response->getStatus());
-		$this->assertEquals(['message' => 'User successfully created'], $response->getData());
+		$this->assertEquals([
+			'message' => 'User successfully created',
+			'username' => 'new@example.com',
+		], $response->getData());
 	}
 
 	/**