feat: allow expressions for TestElement.enabled property

Fixes #6006

Author: vlsi

src/core/src/main/java/org/apache/jmeter/threads/JMeterThread.java

@@ -264,7 +264,10 @@ public void run() {
             iterationListener = initRun(threadContext);
             while (running) {
                 Sampler sam = threadGroupLoopController.next();
-                while (running && sam != null) {
+                for (; running && sam != null; sam = threadGroupLoopController.next()) {
+                    if (!sam.isEnabled()) {
+                        continue;
+                    }
                     processSampler(sam, null, threadContext);
                     threadContext.cleanAfterSample();
 
@@ -296,11 +299,8 @@ public void run() {
                             }
                         }
                         threadContext.setTestLogicalAction(TestLogicalAction.CONTINUE);
-                        sam = null;
                         setLastSampleOk(threadContext.getVariables(), true);
-                    }
-                    else {
-                        sam = threadGroupLoopController.next();
+                        break;
                     }
                 }
 
@@ -898,6 +898,9 @@ private void stopThread() {
 
     private static void checkAssertions(List<? extends Assertion> assertions, SampleResult parent, JMeterContext threadContext) {
         for (Assertion assertion : assertions) {
+            if (!((TestElement) assertion).isEnabled()) {
+                continue;
+            }
             TestBeanHelper.prepare((TestElement) assertion);
             if (assertion instanceof AbstractScopedAssertion scopedAssertion) {
                 String scope = scopedAssertion.fetchScope();
@@ -965,13 +968,19 @@ private static void processAssertion(SampleResult result, Assertion assertion) {
 
     private static void runPostProcessors(List<? extends PostProcessor> extractors) {
         for (PostProcessor ex : extractors) {
+            if (!((TestElement) ex).isEnabled()) {
+                continue;
+            }
             TestBeanHelper.prepare((TestElement) ex);
             ex.process();
         }
     }
 
     private static void runPreProcessors(List<? extends PreProcessor> preProcessors) {
         for (PreProcessor ex : preProcessors) {
+            if (!((TestElement) ex).isEnabled()) {
+                continue;
+            }
             if (log.isDebugEnabled()) {
                 log.debug("Running preprocessor: {}", ((AbstractTestElement) ex).getName());
             }
@@ -992,6 +1001,9 @@ private static void runPreProcessors(List<? extends PreProcessor> preProcessors)
     private void delay(List<? extends Timer> timers) {
         long totalDelay = 0;
         for (Timer timer : timers) {
+            if (!((TestElement) timer).isEnabled()) {
+                continue;
+            }
             TestBeanHelper.prepare((TestElement) timer);
             long delay = timer.delay();
             if (APPLY_TIMER_FACTOR && timer.isModifiable()) {

src/core/src/main/java/org/apache/jmeter/threads/ListenerNotifier.java

@@ -54,6 +54,9 @@ public class ListenerNotifier implements Serializable {
     public void notifyListeners(SampleEvent res, List<SampleListener> listeners) {
         for (SampleListener sampleListener : listeners) {
             try {
+                if (!((TestElement) sampleListener).isEnabled()) {
+                    continue;
+                }
                 TestBeanHelper.prepare((TestElement) sampleListener);
                 sampleListener.sampleOccurred(res);
             } catch (RuntimeException e) {

src/functions/src/test/kotlin/org/apache/jmeter/control/EnabledWithVariablesTest.kt

@@ -0,0 +1,61 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to you under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.jmeter.control
+
+import org.apache.jmeter.junit.JMeterTestCase
+import org.apache.jmeter.sampler.DebugSampler
+import org.apache.jmeter.test.assertions.executePlanAndCollectEvents
+import org.apache.jmeter.threads.ThreadGroup
+import org.apache.jmeter.treebuilder.TreeBuilder
+import org.junit.jupiter.api.Assertions
+import org.junit.jupiter.api.Test
+import kotlin.time.Duration.Companion.seconds
+
+class EnabledWithVariablesTest : JMeterTestCase() {
+    fun TreeBuilder.oneThread(loops: Int, body: ThreadGroup.() -> Unit) {
+        ThreadGroup::class {
+            numThreads = 1
+            rampUp = 0
+            setSamplerController(
+                LoopController().apply {
+                    this.loops = loops
+                }
+            )
+            body()
+        }
+    }
+
+    @Test
+    fun `sampler with conditional enable function`() {
+        val events = executePlanAndCollectEvents(5.seconds) {
+            oneThread(loops = 4) {
+                DebugSampler::class {
+                    name = "Conditionally enabled: \${__jm____idx}"
+                    props {
+                        it[enabled] = "\${__javaScript(vars.get('__jm____idx')%2==1)}"
+                    }
+                }
+            }
+        }
+        Assertions.assertEquals(
+            "[Conditionally enabled: 1, Conditionally enabled: 3]",
+            events.map { it.result.sampleLabel }.toString(),
+            "Test should complete within reasonable time, and the test has 2 debug samplers, so we expect 2 events"
+        )
+    }
+}