Hide virtual field accessor interface methods from reflection

instrumentation/internal/internal-reflection/javaagent-integration-tests/src/test/groovy/ReflectionTest.groovy

@@ -35,5 +35,18 @@ class ReflectionTest extends AgentInstrumentationSpecification {
       }
     }
     methodFound == false
+
+    and:
+    def interfaceClass = TestClass.getInterfaces().find {
+      it.getName().contains("VirtualFieldAccessor\$")
+    }
+    interfaceClass != null
+    def interfaceMethodFound = false
+    for (Method method : interfaceClass.getDeclaredMethods()) {
+      if (method.getName().contains("__opentelemetry")) {
+        interfaceMethodFound = true
+      }
+    }
+    interfaceMethodFound == false
   }
 }

instrumentation/internal/internal-reflection/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/internal/reflection/ReflectionHelper.java

@@ -22,7 +22,7 @@ public static Field[] filterFields(Class<?> containingClass, Field[] fields) {
     }
     List<Field> result = new ArrayList<>(fields.length);
     for (Field field : fields) {
-      // FieldBackedProvider marks added fields as synthetic
+      // virtual fields are marked as synthetic
       if (field.isSynthetic() && field.getName().startsWith("__opentelemetryVirtualField$")) {
         continue;
       }
@@ -32,13 +32,20 @@ public static Field[] filterFields(Class<?> containingClass, Field[] fields) {
   }
 
   public static Method[] filterMethods(Class<?> containingClass, Method[] methods) {
-    if (methods.length == 0
-        || !VirtualFieldInstalledMarker.class.isAssignableFrom(containingClass)) {
+    if (methods.length == 0) {
+      return methods;
+    } else if (containingClass.isInterface()
+        && containingClass.isSynthetic()
+        && containingClass.getName().contains("VirtualFieldAccessor$")) {
+      // hide all methods from virtual field accessor interfaces
+      return new Method[0];
+    } else if (!VirtualFieldInstalledMarker.class.isAssignableFrom(containingClass)) {
+      // nothing to filter when class does not have any added virtual fields
       return methods;
     }
     List<Method> result = new ArrayList<>(methods.length);
     for (Method method : methods) {
-      // FieldBackedProvider marks added method as synthetic
+      // virtual field accessor methods are marked as synthetic
       if (method.isSynthetic()
           && (method.getName().startsWith("get__opentelemetryVirtualField$")
               || method.getName().startsWith("set__opentelemetryVirtualField$"))) {

javaagent-tooling/src/main/java/io/opentelemetry/javaagent/tooling/field/FieldAccessorInterfacesGenerator.java

@@ -54,10 +54,17 @@ private DynamicType.Unloaded<?> makeFieldAccessorInterface(
         .makeInterface()
         .merge(SyntheticState.SYNTHETIC)
         .name(getFieldAccessorInterfaceName(typeName, fieldTypeName))
-        .defineMethod(getRealGetterName(typeName, fieldTypeName), fieldTypeDesc, Visibility.PUBLIC)
+        .defineMethod(
+            getRealGetterName(typeName, fieldTypeName),
+            fieldTypeDesc,
+            Visibility.PUBLIC,
+            SyntheticState.SYNTHETIC)
         .withoutCode()
         .defineMethod(
-            getRealSetterName(typeName, fieldTypeName), TypeDescription.VOID, Visibility.PUBLIC)
+            getRealSetterName(typeName, fieldTypeName),
+            TypeDescription.VOID,
+            Visibility.PUBLIC,
+            SyntheticState.SYNTHETIC)
         .withParameter(fieldTypeDesc, "value")
         .withoutCode()
         .make();