Allow passing counter metric name to datapoint to show in case of validation error

prometheus-metrics-model/src/main/java/io/prometheus/metrics/model/snapshots/CounterSnapshot.java

@@ -56,7 +56,17 @@ public CounterDataPointSnapshot(
         Exemplar exemplar,
         long createdTimestampMillis,
         long scrapeTimestampMillis) {
-      super(labels, createdTimestampMillis, scrapeTimestampMillis);
+      this(null, value, labels, exemplar, createdTimestampMillis, scrapeTimestampMillis);
+    }
+
+    public CounterDataPointSnapshot(
+        String metricName,
+        double value,
+        Labels labels,
+        Exemplar exemplar,
+        long createdTimestampMillis,
+        long scrapeTimestampMillis) {
+      super(metricName, labels, createdTimestampMillis, scrapeTimestampMillis);
       this.value = value;
       this.exemplar = exemplar;
       validate();
@@ -73,7 +83,7 @@ public Exemplar getExemplar() {
 
     protected void validate() {
       if (value < 0.0) {
-        throw new IllegalArgumentException(value + ": counters cannot have a negative value");
+        throw new IllegalArgumentException((getMetricName() == null ? "" : getMetricName() + "=") + value + ": counters cannot have a negative value");
       }
     }
 
@@ -83,6 +93,7 @@ public static Builder builder() {
 
     public static class Builder extends DataPointSnapshot.Builder<Builder> {
 
+      private String metricName = null;
       private Exemplar exemplar = null;
       private Double value = null;
       private long createdTimestampMillis = 0L;
@@ -105,12 +116,17 @@ public Builder createdTimestampMillis(long createdTimestampMillis) {
         return this;
       }
 
+      public Builder metricName(String metricName) {
+        this.metricName = metricName;
+        return this;
+      }
+
       public CounterDataPointSnapshot build() {
         if (value == null) {
           throw new IllegalArgumentException("Missing required field: value is null.");
         }
         return new CounterDataPointSnapshot(
-            value, labels, exemplar, createdTimestampMillis, scrapeTimestampMillis);
+            metricName, value, labels, exemplar, createdTimestampMillis, scrapeTimestampMillis);
       }
 
       @Override

prometheus-metrics-model/src/main/java/io/prometheus/metrics/model/snapshots/DataPointSnapshot.java

@@ -1,19 +1,30 @@
 package io.prometheus.metrics.model.snapshots;
 
 public abstract class DataPointSnapshot {
+  private final String metricName;
   private final Labels labels;
   private final long createdTimestampMillis;
   private final long scrapeTimestampMillis;
 
   protected DataPointSnapshot(
-      Labels labels, long createdTimestampMillis, long scrapeTimestampMillis) {
+          Labels labels, long createdTimestampMillis, long scrapeTimestampMillis) {
+    this(null, labels, createdTimestampMillis, scrapeTimestampMillis);
+  }
+
+  protected DataPointSnapshot(
+          String metricName, Labels labels, long createdTimestampMillis, long scrapeTimestampMillis) {
+    this.metricName = metricName;
     this.labels = labels;
     this.createdTimestampMillis = createdTimestampMillis;
     this.scrapeTimestampMillis = scrapeTimestampMillis;
     validate();
   }
 
   private void validate() {
+    if (metricName != null && metricName.trim().isEmpty()) {
+      throw new IllegalArgumentException("Metric name cannot be an empty string");
+    }
+
     if (labels == null) {
       throw new IllegalArgumentException(
           "Labels cannot be null. Use Labels.EMPTY if there are no labels.");
@@ -60,6 +71,10 @@ public long getCreatedTimestampMillis() {
     return createdTimestampMillis;
   }
 
+  public String getMetricName() {
+    return metricName;
+  }
+
   public abstract static class Builder<T extends Builder<T>> {
 
     protected Labels labels = Labels.EMPTY;