[JENKINS-26761] Recover gracefully from null WorkflowRun.checkouts, p…

…rinting some diagnostics.

job/src/main/java/org/jenkinsci/plugins/workflow/job/WorkflowJob.java

@@ -439,7 +439,7 @@ public void addTrigger(Trigger trigger) {
             return Collections.emptySet();
         }
         List<SCM> scms = new LinkedList<SCM>();
-        for (WorkflowRun.SCMCheckout co : b.checkouts) {
+        for (WorkflowRun.SCMCheckout co : b.checkouts(null)) {
             scms.add(co.scm);
         }
         return scms;
@@ -464,7 +464,7 @@ public void addTrigger(Trigger trigger) {
             listener.getLogger().println("no previous build to compare to");
             return PollingResult.NO_CHANGES;
         }
-        for (WorkflowRun.SCMCheckout co : b.checkouts) {
+        for (WorkflowRun.SCMCheckout co : b.checkouts(listener)) {
             if (!co.scm.supportsPolling()) {
                 listener.getLogger().println("polling not supported from " + co.workspace + " on " + co.node);
             }

job/src/main/java/org/jenkinsci/plugins/workflow/job/WorkflowRun.java

@@ -118,7 +118,8 @@ public final class WorkflowRun extends Run<WorkflowJob,WorkflowRun> implements Q
     /** map from node IDs to log positions from which we should copy text */
     private Map<String,Long> logsToCopy;
 
-    List<SCMCheckout> checkouts;
+    /** JENKINS-26761: supposed to always be set but sometimes is not. Access only through {@link #checkouts(TaskListener)}. */
+    private @CheckForNull List<SCMCheckout> checkouts;
     // TODO could use a WeakReference to reduce memory, but that complicates how we add to it incrementally; perhaps keep a List<WeakReference<ChangeLogSet<?>>>
     private transient List<ChangeLogSet<? extends ChangeLogSet.Entry>> changeSets;
 
@@ -128,6 +129,7 @@ public final class WorkflowRun extends Run<WorkflowJob,WorkflowRun> implements Q
     public WorkflowRun(WorkflowJob job) throws IOException {
         super(job);
         firstTime = true;
+        checkouts = new LinkedList<SCMCheckout>();
         //System.err.printf("created %s @%h%n", this, this);
     }
 
@@ -178,7 +180,6 @@ public WorkflowRun(WorkflowJob job, File dir) throws IOException {
                 listener.error("No flow definition, cannot run");
                 return;
             }
-            checkouts = new LinkedList<SCMCheckout>();
             Owner owner = new Owner(this);
 
             FlowExecution newExecution = definition.create(owner, listener, getAllActions());
@@ -443,6 +444,7 @@ private String key() {
                 Queue.getInstance().schedule(new AfterRestartTask(this), 0);
             }
         }
+        checkouts(null); // only for diagnostics
         synchronized (LOADING_RUNS) {
             LOADING_RUNS.remove(key()); // or could just make the value type be WeakReference<WorkflowRun>
             LOADING_RUNS.notifyAll();
@@ -522,15 +524,23 @@ public boolean hasntStartedYet() {
         return isBuilding(); // there is no equivalent to a post-production state for flows
     }
 
+    synchronized @Nonnull List<SCMCheckout> checkouts(@CheckForNull TaskListener listener) {
+        if (checkouts == null) {
+            LOGGER.log(Level.WARNING, "JENKINS-26761: no checkouts in {0}", this);
+            if (listener != null) {
+                listener.error("JENKINS-26761: list of SCM checkouts in " + this + " was lost; polling will be broken");
+            }
+            checkouts = new LinkedList<SCMCheckout>();
+            // Could this.save(), but might pollute diagnosis, and (worse) might clobber real data if there is >1 WorkflowRun with the same ID.
+        }
+        return checkouts;
+    }
+
     @Exported
     public synchronized List<ChangeLogSet<? extends ChangeLogSet.Entry>> getChangeSets() {
         if (changeSets == null) {
             changeSets = new ArrayList<ChangeLogSet<? extends ChangeLogSet.Entry>>();
-            if (checkouts == null) {
-                LOGGER.log(Level.WARNING, "no checkouts in {0}", this);
-                return changeSets;
-            }
-            for (SCMCheckout co : checkouts) {
+            for (SCMCheckout co : checkouts(null)) {
                 if (co.changelogFile != null && co.changelogFile.isFile()) {
                     try {
                         changeSets.add(co.scm.createChangeLogParser().parse(this, co.scm.getEffectiveBrowser(), co.changelogFile));
@@ -553,7 +563,7 @@ public synchronized HttpResponse doStop() {
         }
     }
 
-    private void onCheckout(SCM scm, FilePath workspace, @CheckForNull File changelogFile, @CheckForNull SCMRevisionState pollingBaseline) throws Exception {
+    private void onCheckout(SCM scm, FilePath workspace, TaskListener listener, @CheckForNull File changelogFile, @CheckForNull SCMRevisionState pollingBaseline) throws Exception {
         if (changelogFile != null && changelogFile.isFile()) {
             ChangeLogSet<?> cls = scm.createChangeLogParser().parse(this, scm.getEffectiveBrowser(), changelogFile);
             getChangeSets().add(cls);
@@ -566,7 +576,7 @@ private void onCheckout(SCM scm, FilePath workspace, @CheckForNull File changelo
         if (computer == null) {
             throw new IllegalStateException();
         }
-        checkouts.add(new SCMCheckout(scm, computer.getName(), workspace.getRemote(), changelogFile, pollingBaseline));
+        checkouts(listener).add(new SCMCheckout(scm, computer.getName(), workspace.getRemote(), changelogFile, pollingBaseline));
     }
 
     static final class SCMCheckout {
@@ -716,7 +726,7 @@ static void alias() {
     @Extension public static final class SCMListenerImpl extends SCMListener {
         @Override public void onCheckout(Run<?,?> build, SCM scm, FilePath workspace, TaskListener listener, File changelogFile, SCMRevisionState pollingBaseline) throws Exception {
             if (build instanceof WorkflowRun) {
-                ((WorkflowRun) build).onCheckout(scm, workspace, changelogFile, pollingBaseline);
+                ((WorkflowRun) build).onCheckout(scm, workspace, listener, changelogFile, pollingBaseline);
             }
         }
     }