App start: Create transaction when no SentryNavigatorObserver is present

CHANGELOG.md

@@ -8,6 +8,7 @@
 
 ### Features
 
+- Create app start transaction when no `SentryNavigatorObserver` is present ([#2017](https://github.com/getsentry/sentry-dart/pull/2017))
 - Adds native spans to app start transaction ([#2027](https://github.com/getsentry/sentry-dart/pull/2027))
 - Adds app start spans to first transaction ([#2009](https://github.com/getsentry/sentry-dart/pull/2009))
 

flutter/lib/src/integrations/native_app_start_integration.dart

@@ -1,3 +1,5 @@
+// ignore_for_file: invalid_use_of_internal_member
+
 import 'dart:async';
 
 import 'package:meta/meta.dart';
@@ -96,7 +98,6 @@ class NativeAppStartIntegration extends Integration<SentryFlutterOptions> {
 
       if (options.autoAppStart) {
         // We only assign the current time if it's not already set - this is useful in tests
-        // ignore: invalid_use_of_internal_member
         _native.appStartEnd ??= options.clock();
         appStartEndDateTime = _native.appStartEnd;
 
@@ -129,7 +130,6 @@ class NativeAppStartIntegration extends Integration<SentryFlutterOptions> {
             description: entry.key as String,
           ));
         } catch (e) {
-          // ignore: invalid_use_of_internal_member
           _hub.options.logger(
               SentryLevel.warning, 'Failed to parse native span times: $e');
           continue;
@@ -149,6 +149,25 @@ class NativeAppStartIntegration extends Integration<SentryFlutterOptions> {
           nativeSpanTimes: nativeSpanTimes);
 
       setAppStartInfo(appStartInfo);
+
+      // When we don't have a SentryNavigatorObserver, a TTID transaction
+      // is not created therefore we need to create a transaction ourselves.
+      // We detect this by checking if the currentRouteName is null.
+      // This is a workaround since there is no api that tells us if
+      // the navigator observer exists or not. The currentRouteName is always
+      // set during a didPush triggered by the navigator observer.
+      if (SentryNavigatorObserver.currentRouteName == null) {
+        const screenName = SentryNavigatorObserver.rootScreenName;
+        final transaction = hub.startTransaction(
+            screenName, SentrySpanOperations.uiLoad,
+            startTimestamp: appStartInfo.start);
+        final ttidSpan = transaction.startChild(
+            SentrySpanOperations.uiTimeToInitialDisplay,
+            description: '$screenName initial display',
+            startTimestamp: appStartInfo.start);
+        await ttidSpan.finish(endTimestamp: appStartInfo.end);
+        await transaction.finish(endTimestamp: appStartInfo.end);
+      }
     });
 
     options.addEventProcessor(NativeAppStartEventProcessor(_native, hub: hub));

flutter/lib/src/navigation/sentry_navigator_observer.dart

@@ -224,7 +224,7 @@ class SentryNavigatorObserver extends RouteObserver<PageRoute<dynamic>> {
     }
 
     if (name == '/') {
-      name = 'root /';
+      name = rootScreenName;
     }
     final transactionContext = SentryTransactionContext(
       name,
@@ -366,6 +366,9 @@ class SentryNavigatorObserver extends RouteObserver<PageRoute<dynamic>> {
     _completedDisplayTracking = Completer();
     _timeToDisplayTracker?.clear();
   }
+
+  @internal
+  static const String rootScreenName = 'root /';
 }
 
 /// This class makes it easier to record breadcrumbs for events of Flutters

flutter/test/integrations/native_app_start_integration_test.dart

@@ -12,13 +12,25 @@ import '../mocks.dart';
 import '../mocks.mocks.dart';
 
 void main() {
+  void setupMocks(Fixture fixture) {
+    when(fixture.hub.startTransaction('root /', 'ui.load',
+            description: null, startTimestamp: anyNamed('startTimestamp')))
+        .thenReturn(fixture.createTracer());
+    when(fixture.hub.configureScope(captureAny)).thenAnswer((_) {});
+    when(fixture.hub
+            .captureTransaction(any, traceContext: anyNamed('traceContext')))
+        .thenAnswer((_) async => SentryId.empty());
+  }
+
   group('$NativeAppStartIntegration', () {
     late Fixture fixture;
 
     setUp(() {
       TestWidgetsFlutterBinding.ensureInitialized();
 
       fixture = Fixture();
+      setupMocks(fixture);
+
       NativeAppStartIntegration.clearAppStartInfo();
     });
 
@@ -257,6 +269,7 @@ void main() {
       SentryFlutter.sentrySetupStartTime =
           DateTime.fromMillisecondsSinceEpoch(15);
 
+      setupMocks(fixture);
       fixture.getNativeAppStartIntegration().call(fixture.hub, fixture.options);
 
       final processor = fixture.options.eventProcessors.first;