fix(auth): validate display name only when required in sign-up form

auth/src/main/java/com/firebase/ui/auth/ui/screens/email/SignUpUI.kt

@@ -95,7 +95,7 @@ fun SignUpUI(
     val isFormValid = remember(displayName, email, password, confirmPassword) {
         derivedStateOf {
             listOf(
-                displayNameValidator.validate(displayName),
+                !provider.isDisplayNameRequired || displayNameValidator.validate(displayName),
                 emailValidator.validate(email),
                 passwordValidator.validate(password),
                 confirmPasswordValidator.validate(confirmPassword)

auth/src/test/java/com/firebase/ui/auth/ui/screens/email/SignUpUITest.kt

@@ -0,0 +1,115 @@
+/*
+ * Copyright 2025 Google Inc. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the
+ * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+ * express or implied. See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.firebase.ui.auth.ui.screens.email
+
+import android.content.Context
+import androidx.compose.runtime.CompositionLocalProvider
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.test.assertIsEnabled
+import androidx.compose.ui.test.hasClickAction
+import androidx.compose.ui.test.hasText
+import androidx.compose.ui.test.junit4.createComposeRule
+import androidx.compose.ui.test.onNodeWithText
+import androidx.compose.ui.test.performTextInput
+import androidx.test.core.app.ApplicationProvider
+import com.firebase.ui.auth.configuration.authUIConfiguration
+import com.firebase.ui.auth.configuration.auth_provider.AuthProvider
+import com.firebase.ui.auth.configuration.string_provider.AuthUIStringProvider
+import com.firebase.ui.auth.configuration.string_provider.DefaultAuthUIStringProvider
+import com.firebase.ui.auth.configuration.string_provider.LocalAuthUIStringProvider
+import org.junit.Before
+import org.junit.Rule
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.annotation.Config
+
+/**
+ * Unit tests for [SignUpUI], covering form validity logic.
+ *
+ * @suppress Internal test class
+ */
+@Config(sdk = [34])
+@RunWith(RobolectricTestRunner::class)
+class SignUpUITest {
+
+    @get:Rule
+    val composeTestRule = createComposeRule()
+
+    private lateinit var applicationContext: Context
+    private lateinit var stringProvider: AuthUIStringProvider
+
+    @Before
+    fun setUp() {
+        applicationContext = ApplicationProvider.getApplicationContext()
+        stringProvider = DefaultAuthUIStringProvider(applicationContext)
+    }
+
+    @Test
+    fun `sign up button becomes enabled when display name is not required and hidden`() {
+        val provider = AuthProvider.Email(
+            isDisplayNameRequired = false,
+            emailLinkActionCodeSettings = null,
+            passwordValidationRules = emptyList()
+        )
+        val configuration = authUIConfiguration {
+            context = applicationContext
+            providers { provider(provider) }
+        }
+
+        composeTestRule.setContent {
+            CompositionLocalProvider(LocalAuthUIStringProvider provides stringProvider) {
+                var email by remember { mutableStateOf("") }
+                var password by remember { mutableStateOf("") }
+                var confirmPassword by remember { mutableStateOf("") }
+
+                SignUpUI(
+                    configuration = configuration,
+                    isLoading = false,
+                    displayName = "",
+                    email = email,
+                    password = password,
+                    confirmPassword = confirmPassword,
+                    onDisplayNameChange = { },
+                    onEmailChange = { email = it },
+                    onPasswordChange = { password = it },
+                    onConfirmPasswordChange = { confirmPassword = it },
+                    onGoToSignIn = { },
+                    onSignUpClick = { }
+                )
+            }
+        }
+
+        // Name field should not be rendered since it isn't required.
+        composeTestRule.onNodeWithText(stringProvider.nameHint).assertDoesNotExist()
+
+        composeTestRule.onNodeWithText(stringProvider.emailHint)
+            .performTextInput("test@example.com")
+        composeTestRule.onNodeWithText(stringProvider.passwordHint)
+            .performTextInput("Password123")
+        composeTestRule.onNodeWithText(stringProvider.confirmPasswordHint)
+            .performTextInput("Password123")
+
+        composeTestRule.waitForIdle()
+
+        // With email/password/confirmPassword all valid and no display name required,
+        // the sign up button should be enabled even though displayName is still "".
+        composeTestRule.onNode(hasText(stringProvider.signupPageTitle.uppercase()) and hasClickAction())
+            .assertIsEnabled()
+    }
+}