Fix "Discovered unresolved method during parsing: org.datadog.jmxfetch.App.<init>(org.datadog.jmxfetch.AppConfig)."

Author: ygree

dd-java-agent/instrumentation/graal/native-image/src/main/java/datadog/trace/instrumentation/graal/nativeimage/AnnotationSubstitutionProcessorInstrumentation.java

@@ -37,7 +37,9 @@ public void methodAdvice(MethodTransformer transformer) {
   public String[] helperClassNames() {
     return new String[] {
       packageName + ".Target_datadog_jctools_counters_FixedSizeStripedLongCounterFields",
-      packageName + ".Target_datadog_jctools_util_UnsafeRefArrayAccess"
+      packageName + ".Target_datadog_jctools_util_UnsafeRefArrayAccess",
+      packageName + ".Target_org_datadog_jmxfetch_App",
+      "com.fasterxml.jackson.core.JsonProcessingException" // loaded by Target_org_datadog_jmxfetch_App
     };
   }
 
@@ -49,7 +51,8 @@ public String[] muzzleIgnoredClassNames() {
       "jdk.vm.ci.meta.ResolvedJavaField",
       // ignore helper class names as usual
       packageName + ".Target_datadog_jctools_counters_FixedSizeStripedLongCounterFields",
-      packageName + ".Target_datadog_jctools_util_UnsafeRefArrayAccess"
+      packageName + ".Target_datadog_jctools_util_UnsafeRefArrayAccess",
+      packageName + ".Target_org_datadog_jmxfetch_App"
     };
   }
 
@@ -58,6 +61,7 @@ public static class FindTargetClassesAdvice {
     public static void onExit(@Advice.Return(readOnly = false) List<Class<?>> result) {
       result.add(Target_datadog_jctools_counters_FixedSizeStripedLongCounterFields.class);
       result.add(Target_datadog_jctools_util_UnsafeRefArrayAccess.class);
+      result.add(Target_org_datadog_jmxfetch_App.class);
     }
   }
 }

dd-java-agent/instrumentation/graal/native-image/src/main/java/datadog/trace/instrumentation/graal/nativeimage/Target_org_datadog_jmxfetch_App.java

@@ -0,0 +1,20 @@
+package datadog.trace.instrumentation.graal.nativeimage;
+
+import com.oracle.svm.core.annotate.Substitute;
+import com.oracle.svm.core.annotate.TargetClass;
+
+@TargetClass(className = "org.datadog.jmxfetch.App")
+public final class Target_org_datadog_jmxfetch_App {
+  @Substitute
+  private boolean getJsonConfigs() {
+    // Remove getJsonConfigs body to fix the GraalVM native build error.
+    //
+    // This method is not needed in Java Tracer, so we exclude next transitive dependencies when embedding JMXFetch:
+    // - jackson-core (catch JsonProcessingException)
+    // - jackson-jr-objects (referenced in org.datadog.jmxfetch.JsonParser).
+    // But GraalVM Native detects it during the reachability analysis and results in
+    // "Discovered unresolved method during parsing: org.datadog.jmxfetch.App.<init>(org.datadog.jmxfetch.AppConfig)."
+    // because of the missing classes that belong to the excluded dependencies.
+    return false;
+  }
+}