timing api uses span duration as value for the emitted metric if possible

Author: stefanosiano

dart/lib/src/metrics/metrics_api.dart

@@ -138,13 +138,17 @@ class MetricsApi {
       }
     } finally {
       final after = _hub.options.clock();
-      final duration = after.difference(before);
+      Duration duration = after.difference(before);
+      // If we have a span, we use its duration as value for the emitted metric
+      if (span != null) {
+        await span.finish();
+        duration =
+            span.endTimestamp?.difference(span.startTimestamp) ?? duration;
+      }
       final value = _convertMicrosTo(unit, duration.inMicroseconds);
 
       _hub.metricsAggregator?.emit(MetricType.distribution, key, value, unit,
           _enrichWithDefaultTags(tags));
-
-      await span?.finish();
     }
   }
 
@@ -156,7 +160,7 @@ class MetricsApi {
       case DurationSentryMeasurementUnit.microSecond:
         return micros.toDouble();
       case DurationSentryMeasurementUnit.milliSecond:
-        return micros / 1000;
+        return micros / 1000.0;
       case DurationSentryMeasurementUnit.second:
         return micros / 1000000.0;
       case DurationSentryMeasurementUnit.minute:

dart/test/metrics/metrics_api_test.dart

@@ -102,6 +102,7 @@ void main() {
       final delay = Duration(milliseconds: 100);
       final completer = Completer<void>();
       fixture._options.tracesSampleRate = 1;
+      fixture._options.enableMetrics = true;
       MetricsApi api = fixture.getSut(hub: fixture.hub);
 
       // Start a transaction so that timing api can start a child span
@@ -114,17 +115,28 @@ void main() {
 
       // Timing starts a span
       api.timing('my key',
+          unit: DurationSentryMeasurementUnit.milliSecond,
           function: () => Future.delayed(delay, () => completer.complete()));
       final span = transaction.children.first;
       expect(span.finished, false);
       expect(span.context.operation, 'metric.timing');
       expect(span.context.description, 'my key');
-      final spanDuration = span.endTimestamp!.difference(span.startTimestamp);
 
       // Timing finishes the span when the function is finished, which takes 100 milliseconds
       await completer.future;
-      expect(spanDuration.inMilliseconds >= 100, true);
       expect(span.finished, true);
+      final spanDuration = span.endTimestamp!.difference(span.startTimestamp);
+      expect(spanDuration.inMilliseconds >= 100, true);
+      await Future.delayed(Duration());
+
+      Iterable<Metric> sentMetrics =
+          fixture.hub.metricsAggregator!.buckets.values.first.values;
+
+      // The emitted metric value should match the span duration
+      expect(sentMetrics.first.unit, DurationSentryMeasurementUnit.milliSecond);
+      // Duration.inMilliseconds returns an int, so we have to assert it
+      expect((sentMetrics.first as DistributionMetric).values.first.toInt(),
+          spanDuration.inMilliseconds);
     });
   });
 }