fix: transaction timestamp trimming (#1916)

* Fix child timestamp trimming

* Update CHANGELOG

* Run formatting

* Update docs

* Revert

* Update dart/test/sentry_tracer_test.dart

Co-authored-by: Philipp Hofmann <philipp.hofmann@sentry.io>

* change var to final

* fix test

---------

Co-authored-by: Philipp Hofmann <philipp.hofmann@sentry.io>

CHANGELOG.md

@@ -2,6 +2,11 @@
 
 ## Unreleased
 
+### Fixes
+
+- Fix transaction end timestamp trimming ([#1916](https://github.com/getsentry/sentry-dart/pull/1916))
+  - Transaction end timestamps are now correctly trimmed to the latest child span end timestamp
+
 ### Features
 
 - Use `recordHttpBreadcrumbs` to set iOS `enableNetworkBreadcrumbs` ([#1884](https://github.com/getsentry/sentry-dart/pull/1884))

dart/lib/src/sentry_tracer.dart

@@ -109,18 +109,24 @@ class SentryTracer extends ISentrySpan {
       }
 
       var _rootEndTimestamp = commonEndTimestamp;
+
+      // Trim the end timestamp of the transaction to the very last timestamp of child spans
       if (_trimEnd && children.isNotEmpty) {
-        final childEndTimestamps = children
-            .where((child) => child.endTimestamp != null)
-            .map((child) => child.endTimestamp!);
-
-        if (childEndTimestamps.isNotEmpty) {
-          final oldestChildEndTimestamp =
-              childEndTimestamps.reduce((a, b) => a.isAfter(b) ? a : b);
-          if (_rootEndTimestamp.isAfter(oldestChildEndTimestamp)) {
-            _rootEndTimestamp = oldestChildEndTimestamp;
+        DateTime? latestEndTime;
+
+        for (final child in children) {
+          final childEndTimestamp = child.endTimestamp;
+          if (childEndTimestamp != null) {
+            if (latestEndTime == null ||
+                childEndTimestamp.isAfter(latestEndTime)) {
+              latestEndTime = child.endTimestamp;
+            }
           }
         }
+
+        if (latestEndTime != null) {
+          _rootEndTimestamp = latestEndTime;
+        }
       }
 
       // the callback should run before because if the span is finished,

dart/test/sentry_tracer_test.dart

@@ -386,6 +386,28 @@ void main() {
       expect(sut.endTimestamp, endTimestamp);
     });
 
+    test('end trimmed to latest child end timestamp', () async {
+      final sut = fixture.getSut(trimEnd: true);
+      final rootEndInitial = getUtcDateTime();
+      final childAEnd = rootEndInitial;
+      final childBEnd = rootEndInitial.add(Duration(seconds: 1));
+      final childCEnd = rootEndInitial;
+
+      final childA = sut.startChild('operation-a', description: 'description');
+      final childB = sut.startChild('operation-b', description: 'description');
+      final childC = sut.startChild('operation-c', description: 'description');
+
+      await childA.finish(endTimestamp: childAEnd);
+      await childB.finish(endTimestamp: childBEnd);
+      await childC.finish(endTimestamp: childCEnd);
+
+      await sut.finish(endTimestamp: rootEndInitial);
+
+      expect(sut.endTimestamp, equals(childB.endTimestamp),
+          reason:
+              'The root end timestamp should be updated to match the latest child end timestamp.');
+    });
+
     test('does not add more spans than configured in options', () async {
       fixture.hub.options.maxSpans = 2;
       final sut = fixture.getSut();