Fix serialization of array-valued scope and resource attributes in Prometheus exporter

CHANGELOG.md

@@ -2,6 +2,13 @@
 
 ## Unreleased
 
+### SDK
+
+#### Exporters
+
+* Prometheus: Fix serialization of array-valued scope and resource attributes to JSON strings
+  ([#XXXX](https://github.com/open-telemetry/opentelemetry-java/pull/XXXX))
+
 ## Version 1.63.0 (2026-06-05)
 
 ### API

exporters/prometheus/src/main/java/io/opentelemetry/exporter/prometheus/Otel2PrometheusConverter.java

@@ -561,7 +561,8 @@ private Labels convertAttributes(
           .forEach(
               (key, value) ->
                   labelNameToValue.putIfAbsent(
-                      OTEL_SCOPE_ATTRIBUTE_PREFIX + key.getKey(), value.toString()));
+                      OTEL_SCOPE_ATTRIBUTE_PREFIX + key.getKey(),
+                      toLabelValue(key.getType(), value)));
     }
 
     if (resource != null) {
@@ -570,7 +571,8 @@ private Labels convertAttributes(
         Object attributeValue = resourceAttributes.get(attributeKey);
         if (attributeValue != null) {
           labelNameToValue.putIfAbsent(
-              convertLabelName(attributeKey.getKey()), attributeValue.toString());
+              convertLabelName(attributeKey.getKey()),
+              toLabelValue(attributeKey.getType(), attributeValue));
         }
       }
     }

exporters/prometheus/src/test/java/io/opentelemetry/exporter/prometheus/Otel2PrometheusConverterTest.java

@@ -681,9 +681,56 @@ private static Stream<Arguments> resourceAttributesAdditionArgs() {
             "my_metric_units",
             "cluster=\"mycluster\",otel_scope_foo=\"bar\",otel_scope_name=\"scope\",otel_scope_schema_url=\"schemaUrl\",otel_scope_version=\"version\""));
 
+    // Array-valued resource attribute is serialized as a JSON string, matching the point attribute
+    // path
+    arguments.add(
+        Arguments.argumentSet(
+            "array-valued resource attribute serialized as json",
+            createSampleMetricData(
+                "my.metric",
+                "units",
+                MetricDataType.LONG_SUM,
+                Attributes.empty(),
+                Resource.create(
+                    Attributes.of(stringArrayKey("clusters"), Arrays.asList("a", "b")))),
+            /* allowedResourceAttributesFilter= */ Predicates.startsWith("clu"),
+            "my_metric_units",
+            "clusters=\"[\\\"a\\\",\\\"b\\\"]\",otel_scope_foo=\"bar\",otel_scope_name=\"scope\",otel_scope_schema_url=\"schemaUrl\",otel_scope_version=\"version\""));
+
     return arguments.stream();
   }
 
+  @Test
+  void arrayValuedScopeAttributeSerializedAsJson() {
+    // Array-valued scope attribute is serialized as a JSON string, matching the point attribute
+    // path
+    InstrumentationScopeInfo scope =
+        InstrumentationScopeInfo.builder("scope")
+            .setAttributes(Attributes.of(stringArrayKey("foo"), Arrays.asList("a", "b")))
+            .build();
+    MetricData metricData =
+        ImmutableMetricData.createLongSum(
+            Resource.getDefault(),
+            scope,
+            "sample",
+            "description",
+            "1",
+            ImmutableSumData.create(
+                /* isMonotonic= */ true,
+                AggregationTemporality.CUMULATIVE,
+                Collections.singletonList(
+                    ImmutableLongPointData.create(0, 1, Attributes.empty(), 1L))));
+
+    MetricSnapshots snapshots = converter.convert(Collections.singletonList(metricData));
+
+    Optional<MetricSnapshot> metricSnapshot =
+        snapshots.stream().filter(snapshot -> snapshot instanceof CounterSnapshot).findFirst();
+    assertThat(metricSnapshot).isPresent();
+
+    Labels labels = metricSnapshot.get().getDataPoints().get(0).getLabels();
+    assertThat(labels.get("otel_scope_foo")).isEqualTo("[\"a\",\"b\"]");
+  }
+
   @Test
   void metricNameCollisionTest_Issue6277() {
     // NOTE: Metrics with the same resolved prometheus name should merge. However,