Recover gracefully when a PlaceholderTask is in the queue but the associated build is complete

pom.xml

@@ -71,6 +71,7 @@
         <useBeta>true</useBeta>
         <gitHubRepo>jenkinsci/${project.artifactId}-plugin</gitHubRepo>
         <hpi.compatibleSinceVersion>2.40</hpi.compatibleSinceVersion>
+        <jenkins-test-harness.version>1666.vd1360abbfe9e</jenkins-test-harness.version>
     </properties>
     <dependencyManagement>
         <dependencies>

src/main/java/org/jenkinsci/plugins/workflow/support/steps/ExecutorStepExecution.java

@@ -422,6 +422,22 @@ public String getCookie() {
         }
 
         @Override public CauseOfBlockage getCauseOfBlockage() {
+            Run<?, ?> run = runForDisplay();
+            if (!stopping && run != null && !run.isLogUpdated()) {
+                stopping = true;
+                LOGGER.warning(() -> "Refusing to build " + this + " and cancelling it because associated build is complete");
+                Timer.get().execute(() -> {
+                    Queue.getInstance().cancel(this);
+                });
+            }
+            if (stopping) {
+                return new CauseOfBlockage() {
+                    @Override
+                    public String getShortDescription() {
+                        return "Stopping " + getDisplayName();
+                    }
+                };
+            }
             return null;
         }
 

src/test/java/org/jenkinsci/plugins/workflow/support/steps/ExecutorStepTest.java

@@ -35,6 +35,7 @@
 import hudson.model.FreeStyleProject;
 import hudson.model.Item;
 import hudson.model.Job;
+import hudson.model.Label;
 import hudson.model.Node;
 import hudson.model.Queue;
 import hudson.model.Result;
@@ -79,6 +80,7 @@
 
 import hudson.util.VersionNumber;
 import java.nio.charset.StandardCharsets;
+import java.nio.file.StandardCopyOption;
 import java.util.Set;
 import jenkins.model.Jenkins;
 import jenkins.security.MasterToSlaveCallable;
@@ -1264,6 +1266,46 @@ public void accessPermittedOnlyFromCurrentBuild() throws Throwable {
             r.buildAndAssertSuccess(main);
         });
     }
+
+    @Test public void placeholderTaskInQueueButAssociatedBuildComplete() throws Throwable {
+        logging.record(ExecutorStepExecution.class, Level.FINE).capture(50);
+        Path tempQueueFile = tmp.newFile().toPath();
+        sessions.then(r -> {
+            WorkflowJob p = r.createProject(WorkflowJob.class, "p");
+            p.setDefinition(new CpsFlowDefinition("node('custom-label') { }", true));
+            WorkflowRun b = p.scheduleBuild2(0).waitForStart();
+            // Get into a state where a PlaceholderTask is in the queue.
+            while (true) {
+                Queue.Item[] items = Queue.getInstance().getItems();
+                if (items.length == 1 && items[0].task instanceof ExecutorStepExecution.PlaceholderTask) {
+                    break;
+                }
+                Thread.sleep(500L);
+            }
+            // Copy queue.xml to a temp file while the PlaceholderTask is in the queue.
+            r.jenkins.getQueue().save();
+            Files.copy(sessions.getHome().toPath().resolve("queue.xml"), tempQueueFile, StandardCopyOption.REPLACE_EXISTING);
+            // Create a node with the correct label and let the build complete.
+            DumbSlave node = r.createOnlineSlave(Label.get("custom-label"));
+            r.assertBuildStatusSuccess(r.waitForCompletion(b));
+            // Remove node so that tasks requiring custom-label are stuck in the queue.
+            Jenkins.get().removeNode(node);
+        });
+        // Copy the temp queue.xml over the real one. The associated build has already completed, so the queue now
+        // has a bogus PlaceholderTask.
+        Files.copy(tempQueueFile, sessions.getHome().toPath().resolve("queue.xml"), StandardCopyOption.REPLACE_EXISTING);
+        sessions.then(r -> {
+            WorkflowJob p = r.jenkins.getItemByFullName("p", WorkflowJob.class);
+            WorkflowRun b = p.getBuildByNumber(1);
+            assertFalse(b.isLogUpdated());
+            r.assertBuildStatusSuccess(b);
+            while (Queue.getInstance().getItems().length > 0) {
+                Thread.sleep(100L);
+            }
+            assertThat(logging.getMessages(), hasItem(startsWith("Refusing to build ExecutorStepExecution.PlaceholderTask{runId=p#")));
+        });
+    }
+
     public static final class WriteBackStep extends Step {
         static File controllerFile;
         static boolean legal = true;