fix(auth): log diagnostic warning when Google sign-in NoCredentialException fallback exhausts

auth/src/main/java/com/firebase/ui/auth/configuration/auth_provider/GoogleAuthProvider+FirebaseAuthUI.kt

@@ -158,6 +158,21 @@ internal suspend fun FirebaseAuthUI.signInWithGoogle(
                         autoSelectEnabled = provider.autoSelectEnabled
                     )
                 } catch (fallbackException: NoCredentialException) {
+                    // Credential Manager doesn't distinguish "no account on device" from
+                    // developer-side misconfiguration, so log the possible causes for
+                    // debugging. Never surfaced to end users: the overwhelming majority
+                    // hitting this genuinely have no account, and Firebase Console
+                    // guidance would just confuse them.
+                    Log.w(
+                        "GoogleAuthProvider",
+                        "No credential returned from Credential Manager after trying both " +
+                            "authorized and all accounts. Possible causes: (1) no Google " +
+                            "account on this device, (2) no Android OAuth client / SHA-1 " +
+                            "registered for this app's package + signing certificate in the " +
+                            "Firebase console, or (3) the Credential Manager Google ID " +
+                            "provider is unavailable on this device.",
+                        fallbackException
+                    )
                     // No Google accounts available on device at all
                     throw AuthException.UnknownException(
                         message = "No Google accounts available.\n\nPlease add a Google account to your device and try again.",

auth/src/test/java/com/firebase/ui/auth/configuration/auth_provider/GoogleAuthProviderFirebaseAuthUITest.kt

@@ -15,8 +15,10 @@
 package com.firebase.ui.auth.configuration.auth_provider
 
 import android.content.Context
+import android.util.Log
 import androidx.core.net.toUri
 import androidx.credentials.CredentialManager
+import androidx.credentials.exceptions.NoCredentialException
 import androidx.test.core.app.ApplicationProvider
 import com.firebase.ui.auth.AuthException
 import com.firebase.ui.auth.AuthState
@@ -50,6 +52,7 @@ import org.mockito.kotlin.argumentCaptor
 import org.mockito.kotlin.eq
 import org.robolectric.RobolectricTestRunner
 import org.robolectric.annotation.Config
+import org.robolectric.shadows.ShadowLog
 
 /**
  * Comprehensive unit tests for Google Sign-In provider methods in FirebaseAuthUI.
@@ -437,6 +440,65 @@ class GoogleAuthProviderFirebaseAuthUITest {
         assertThat(errorState.exception).isInstanceOf(AuthException.UnknownException::class.java)
     }
 
+    @Test
+    fun `Sign in with Google when both credential attempts throw NoCredentialException logs diagnostic warning`() = runTest {
+        ShadowLog.clear()
+        val noCredentialException = NoCredentialException("No credential available")
+
+        `when`(
+            mockCredentialManagerProvider.getGoogleCredential(
+                context = eq(applicationContext),
+                credentialManager = any<CredentialManager>(),
+                serverClientId = eq("test-client-id"),
+                filterByAuthorizedAccounts = eq(true),
+                autoSelectEnabled = eq(false)
+            )
+        ).thenAnswer { throw noCredentialException }
+
+        `when`(
+            mockCredentialManagerProvider.getGoogleCredential(
+                context = eq(applicationContext),
+                credentialManager = any<CredentialManager>(),
+                serverClientId = eq("test-client-id"),
+                filterByAuthorizedAccounts = eq(false),
+                autoSelectEnabled = eq(false)
+            )
+        ).thenAnswer { throw noCredentialException }
+
+        val instance = FirebaseAuthUI.create(firebaseApp, mockFirebaseAuth)
+        val googleProvider = AuthProvider.Google(
+            serverClientId = "test-client-id",
+            scopes = emptyList()
+        )
+        val config = authUIConfiguration {
+            context = applicationContext
+            providers {
+                provider(googleProvider)
+            }
+        }
+
+        try {
+            instance.signInWithGoogle(
+                context = applicationContext,
+                config = config,
+                provider = googleProvider,
+                authorizationProvider = mockAuthorizationProvider,
+                credentialManagerProvider = mockCredentialManagerProvider
+            )
+            throw AssertionError("Expected exception to be thrown")
+        } catch (e: AuthException) {
+            // User-facing message stays generic - never mentions Firebase Console/SHA-1
+            assertThat(e).isInstanceOf(AuthException.UnknownException::class.java)
+            assertThat(e.message).contains("No Google accounts available")
+        }
+
+        // Diagnostic detail goes to Logcat only, for developers
+        val diagnosticLog = ShadowLog.getLogs().firstOrNull {
+            it.type == Log.WARN && it.tag == "GoogleAuthProvider" && it.msg.contains("SHA-1")
+        }
+        assertThat(diagnosticLog).isNotNull()
+    }
+
     @Test
     fun `Sign in with Google when Firebase sign-in fails should throw AuthException`() = runTest {
         val mockCredential = mock(AuthCredential::class.java)