Use constant instead of magic values for IsTraceRoot (#9465)

* chore: Use constant instead of magic values for IsTraceRoot

* fix: PR Review

* chore: Extract tristate as an enum

---------

Signed-off-by: Brice Dutheil <[email protected]>

Author: bric3

dd-trace-core/src/main/java/datadog/trace/common/metrics/SerializingMetricWriter.java

@@ -36,6 +36,10 @@ public final class SerializingMetricWriter implements MetricWriter {
   private static final byte[] SPAN_KIND = "SpanKind".getBytes(ISO_8859_1);
   private static final byte[] PEER_TAGS = "PeerTags".getBytes(ISO_8859_1);
 
+  // Constant declared here for compile-time folding
+  public static final int TRISTATE_TRUE = TriState.TRUE.serialValue;
+  public static final int TRISTATE_FALSE = TriState.FALSE.serialValue;
+
   private final WellKnownTags wellKnownTags;
   private final WritableFormatter writer;
   private final Sink sink;
@@ -118,7 +122,7 @@ public void add(MetricKey key, AggregateMetric aggregate) {
     writer.writeBoolean(key.isSynthetics());
 
     writer.writeUTF8(IS_TRACE_ROOT);
-    writer.writeInt(key.isTraceRoot() ? 1 : 2); // tristate (0 unknown, 1 true, 2 false)
+    writer.writeInt(key.isTraceRoot() ? TRISTATE_TRUE : TRISTATE_FALSE);
 
     writer.writeUTF8(SPAN_KIND);
     writer.writeUTF8(key.getSpanKind());

dd-trace-core/src/main/java/datadog/trace/common/metrics/TriState.java

@@ -0,0 +1,16 @@
+package datadog.trace.common.metrics;
+
+/**
+ * TriState is used to represent a three-valued logic: true, false, and unknown. The "integer"
+ * values are used for metrics serialization.
+ */
+public enum TriState {
+  UNKNOWN(0),
+  TRUE(1),
+  FALSE(2);
+  public final int serialValue;
+
+  TriState(int serialValue) {
+    this.serialValue = serialValue;
+  }
+}

dd-trace-core/src/test/groovy/datadog/trace/common/metrics/SerializingMetricWriterTest.groovy

@@ -17,7 +17,6 @@ import static java.util.concurrent.TimeUnit.MILLISECONDS
 import static java.util.concurrent.TimeUnit.SECONDS
 
 class SerializingMetricWriterTest extends DDSpecification {
-
   def "should produce correct message #iterationIndex with process tags enabled #withProcessTags" () {
     setup:
     if (withProcessTags) {
@@ -177,7 +176,7 @@ class SerializingMetricWriterTest extends DDSpecification {
         assert unpacker.unpackBoolean() == key.isSynthetics()
         ++elementCount
         assert unpacker.unpackString() == "IsTraceRoot"
-        assert unpacker.unpackInt() == (key.isTraceRoot() ? 1 : 2)
+        assert unpacker.unpackInt() == (key.isTraceRoot() ? TriState.TRUE.serialValue : TriState.FALSE.serialValue)
         ++elementCount
         assert unpacker.unpackString() == "SpanKind"
         assert unpacker.unpackString() == key.getSpanKind() as String