Introduce builder for PrometheusProperties and a failing unit test in case counter exemplars are disabled in the code definition but specifically enabled for the metric in the properties

Signed-off-by: Jens Wilke <signed-off@cruftex.net>

Author: cruftex

prometheus-metrics-config/src/main/java/io/prometheus/metrics/config/PrometheusProperties.java

@@ -36,6 +36,10 @@ public static PrometheusProperties get() throws PrometheusPropertiesException {
     return instance;
   }
 
+  public static Builder builder() {
+    return new Builder();
+  }
+
   public PrometheusProperties(
       MetricsProperties defaultMetricsProperties,
       Map<String, MetricsProperties> metricProperties,
@@ -95,4 +99,78 @@ public ExporterPushgatewayProperties getExporterPushgatewayProperties() {
   public ExporterOpenTelemetryProperties getExporterOpenTelemetryProperties() {
     return exporterOpenTelemetryProperties;
   }
+
+  public static class Builder {
+    private MetricsProperties defaultMetricsProperties;
+    private Map<String, MetricsProperties> metricProperties = new HashMap<>();
+    private ExemplarsProperties exemplarProperties;
+    private ExporterProperties exporterProperties;
+    private ExporterFilterProperties exporterFilterProperties;
+    private ExporterHttpServerProperties httpServerConfig;
+    private ExporterPushgatewayProperties pushgatewayProperties;
+    private ExporterOpenTelemetryProperties otelConfig;
+
+    private Builder() {}
+
+    public Builder defaultMetricsProperties(MetricsProperties defaultMetricsProperties) {
+      this.defaultMetricsProperties = defaultMetricsProperties;
+      return this;
+    }
+
+    public Builder metricProperties(Map<String, MetricsProperties> metricProperties) {
+      this.metricProperties = metricProperties;
+      return this;
+    }
+
+    /** Convenience for adding a single named MetricsProperties */
+    public Builder putMetricProperty(String name, MetricsProperties props) {
+      this.metricProperties.put(name, props);
+      return this;
+    }
+
+    public Builder exemplarProperties(ExemplarsProperties exemplarProperties) {
+      this.exemplarProperties = exemplarProperties;
+      return this;
+    }
+
+    public Builder exporterProperties(ExporterProperties exporterProperties) {
+      this.exporterProperties = exporterProperties;
+      return this;
+    }
+
+    public Builder exporterFilterProperties(ExporterFilterProperties exporterFilterProperties) {
+      this.exporterFilterProperties = exporterFilterProperties;
+      return this;
+    }
+
+    public Builder httpServerConfig(ExporterHttpServerProperties httpServerConfig) {
+      this.httpServerConfig = httpServerConfig;
+      return this;
+    }
+
+    public Builder pushgatewayProperties(ExporterPushgatewayProperties pushgatewayProperties) {
+      this.pushgatewayProperties = pushgatewayProperties;
+      return this;
+    }
+
+    public Builder otelConfig(ExporterOpenTelemetryProperties otelConfig) {
+      this.otelConfig = otelConfig;
+      return this;
+    }
+
+    public PrometheusProperties build() {
+      return new PrometheusProperties(
+        defaultMetricsProperties,
+        metricProperties,
+        exemplarProperties,
+        exporterProperties,
+        exporterFilterProperties,
+        httpServerConfig,
+        pushgatewayProperties,
+        otelConfig
+      );
+    }
+
+  }
+
 }

prometheus-metrics-core/src/test/java/io/prometheus/metrics/core/metrics/CounterTest.java

@@ -5,6 +5,8 @@
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.assertj.core.data.Offset.offset;
 
+import io.prometheus.metrics.config.MetricsProperties;
+import io.prometheus.metrics.config.PrometheusProperties;
 import io.prometheus.metrics.core.exemplars.ExemplarSamplerConfigTestUtil;
 import io.prometheus.metrics.expositionformats.generated.com_google_protobuf_4_31_1.Metrics;
 import io.prometheus.metrics.expositionformats.internal.PrometheusProtobufWriterImpl;
@@ -319,8 +321,6 @@ void incWithExemplar2() {
   public void testExemplarSamplerDisabled() {
     Counter counter =
         Counter.builder()
-            // .withExemplarSampler((inc, prev) -> {throw new RuntimeException("unexpected call to
-            // exemplar sampler");})
             .name("count_total")
             .withoutExemplars()
             .build();
@@ -330,6 +330,42 @@ public void testExemplarSamplerDisabled() {
     assertThat(getData(counter).getExemplar()).isNull();
   }
 
+  @Test
+  public void testExemplarSamplerDisabled_enabledByDefault() {
+    PrometheusProperties properties = PrometheusProperties.builder()
+      .defaultMetricsProperties(MetricsProperties.builder()
+        .exemplarsEnabled(true)
+        .build())
+      .build();
+    Counter counter =
+      Counter.builder(properties)
+        .name("count_total")
+        .withoutExemplars()
+        .build();
+    counter.incWithExemplar(3.0, Labels.of("a", "b"));
+    assertThat(getData(counter).getExemplar()).isNull();
+    counter.inc(2.0);
+    assertThat(getData(counter).getExemplar()).isNull();
+  }
+
+  @Test
+  public void testExemplarSamplerDisabledInDefinition_enabledByPropertiesOnMetric_FAILING() {
+    PrometheusProperties properties = PrometheusProperties.builder()
+      .putMetricProperty("count", MetricsProperties.builder()
+        .exemplarsEnabled(true)
+        .build())
+      .build();
+    Counter counter =
+      Counter.builder(properties)
+        .name("count_total")
+        .withoutExemplars()
+        .build();
+    counter.incWithExemplar(3.0, Labels.of("a", "b"));
+    assertThat(getData(counter).getExemplar()).isNull();
+    counter.inc(2.0);
+    assertThat(getData(counter).getExemplar()).isNull();
+  }
+
   @Test
   public void testConstLabelsFirst() {
     assertThatExceptionOfType(IllegalArgumentException.class)