Register ConfigInversion netric collector for InstrumenterConfig

InstrumenterConfig runs before Config and checks settings that control instrumentation.
We skip the registration when doing native-image builds because we deliberately turn off
non-critical features like telemetry for native-image.

This change also simplifies ConfigInversionMetricCollectorProvider.get() for performance
reasons, while moving debug logs to NoOpConfigInversionMetricCollector when the telemetry
based implementation is not yet registered.

Author: mcculls

internal-api/src/main/java/datadog/trace/api/InstrumenterConfig.java

@@ -80,6 +80,8 @@
 import static datadog.trace.util.CollectionUtils.tryMakeImmutableSet;
 
 import datadog.trace.api.profiling.ProfilingEnablement;
+import datadog.trace.api.telemetry.ConfigInversionMetricCollectorImpl;
+import datadog.trace.api.telemetry.ConfigInversionMetricCollectorProvider;
 import datadog.trace.api.telemetry.OtelEnvMetricCollectorImpl;
 import datadog.trace.api.telemetry.OtelEnvMetricCollectorProvider;
 import datadog.trace.bootstrap.config.provider.ConfigProvider;
@@ -107,6 +109,14 @@
  * @see Config for other configurations
  */
 public class InstrumenterConfig {
+  static {
+    if (!Platform.isNativeImageBuilder()) {
+      // Bind telemetry collector to config module before initializing ConfigProvider
+      ConfigInversionMetricCollectorProvider.register(
+          ConfigInversionMetricCollectorImpl.getInstance());
+    }
+  }
+
   private final ConfigProvider configProvider;
 
   private final boolean triageEnabled;

utils/config-utils/src/main/java/datadog/trace/api/telemetry/ConfigInversionMetricCollectorProvider.java

@@ -1,23 +1,12 @@
 package datadog.trace.api.telemetry;
 
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
 public final class ConfigInversionMetricCollectorProvider {
-  private static final Logger log =
-      LoggerFactory.getLogger(ConfigInversionMetricCollectorProvider.class);
-  private static ConfigInversionMetricCollector INSTANCE = null;
+  private static ConfigInversionMetricCollector INSTANCE =
+      NoOpConfigInversionMetricCollector.getInstance();
 
   private ConfigInversionMetricCollectorProvider() {}
 
   public static ConfigInversionMetricCollector get() {
-    if (INSTANCE == null) {
-      log.debug(
-          "ConfigInversionMetricCollector has not been registered. Defaulting to NoOp implementation.");
-      // Return NoOp implementation for build tasks like instrumentJava that run before
-      // implementation is registered
-      return NoOpConfigInversionMetricCollector.getInstance();
-    }
     return INSTANCE;
   }
 

utils/config-utils/src/main/java/datadog/trace/api/telemetry/NoOpConfigInversionMetricCollector.java

@@ -1,5 +1,8 @@
 package datadog.trace.api.telemetry;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 /**
  * NOOP implementation of ConfigInversionMetricCollector. Used as a default when the real collector
  * is not registered during build tasks like instrumentJava.
@@ -8,6 +11,9 @@ public final class NoOpConfigInversionMetricCollector implements ConfigInversion
   private static final NoOpConfigInversionMetricCollector INSTANCE =
       new NoOpConfigInversionMetricCollector();
 
+  private static final Logger log =
+      LoggerFactory.getLogger(NoOpConfigInversionMetricCollector.class);
+
   private NoOpConfigInversionMetricCollector() {}
 
   public static NoOpConfigInversionMetricCollector getInstance() {
@@ -16,6 +22,6 @@ public static NoOpConfigInversionMetricCollector getInstance() {
 
   @Override
   public void setUndocumentedEnvVarMetric(String configName) {
-    // NOOP - do nothing
+    log.debug("Environment variable {} is undocumented", configName);
   }
 }