Merge pull request #37 from dwnusbaum/empty-changelog-file

[JENKINS-59560] Delete empty changelog files to avoid issues in WorkflowRun.onCheckout

Author: dwnusbaum

src/main/java/org/jenkinsci/plugins/workflow/steps/scm/SCMStep.java

@@ -122,6 +122,14 @@ public final void checkout(Run<?,?> run, FilePath workspace, TaskListener listen
                 }
             }
             scm.checkout(run, launcher, workspace, listener, changelogFile, baseline);
+            if (changelogFile != null && changelogFile.length() == 0) {
+                // JENKINS-57918/JENKINS-59560: Some SCM plugins don't write anything to the changelog file in some
+                // cases. `WorkflowRun.onCheckout` asks the SCM to parse the changelog file if it exists, and
+                // attempting to parse an empty file will cause an error, so we delete empty files before they even get
+                // to `WorkflowRun.onCheckout`.
+                Files.deleteIfExists(changelogFile.toPath());
+                changelogFile = null;
+            }
             SCMRevisionState pollingBaseline = null;
             if (poll || changelog) {
                 pollingBaseline = scm.calcRevisionsFromBuild(run, workspace, launcher, listener);

src/test/java/org/jenkinsci/plugins/workflow/steps/scm/SCMStepTest.java

@@ -24,15 +24,25 @@
 
 package org.jenkinsci.plugins.workflow.steps.scm;
 
+import hudson.FilePath;
+import hudson.Launcher;
 import hudson.model.Label;
+import hudson.model.Run;
+import hudson.model.TaskListener;
+import hudson.scm.ChangeLogParser;
 import hudson.scm.ChangeLogSet;
+import hudson.scm.NullSCM;
 import hudson.scm.PollingResult;
+import hudson.scm.RepositoryBrowser;
+import hudson.scm.SCMRevisionState;
 import hudson.scm.SubversionSCM;
 import hudson.triggers.SCMTrigger;
 import hudson.util.StreamTaskListener;
 import java.io.File;
+import java.io.IOException;
 import java.util.Iterator;
 import java.util.List;
+import jenkins.model.Jenkins;
 
 import jenkins.plugins.git.GitSampleRepoRule;
 import jenkins.scm.impl.subversion.SubversionSampleRepoRule;
@@ -49,6 +59,9 @@
 import org.jvnet.hudson.test.BuildWatcher;
 import org.jvnet.hudson.test.Issue;
 import org.jvnet.hudson.test.RestartableJenkinsRule;
+import org.jvnet.hudson.test.TestExtension;
+import org.kohsuke.stapler.DataBoundConstructor;
+import org.xml.sax.SAXException;
 
 public class SCMStepTest {
 
@@ -150,8 +163,39 @@ public void scmVars() throws Exception {
             assertPolling(p, PollingResult.Change.SIGNIFICANT);
         });
     }
+
+    @Issue(value = { "JENKINS-57918", "JENKINS-59560" })
+    @Test public void scmParsesUmodifiedChangelogFile() {
+        rr.then(r -> {
+            WorkflowJob p = r.jenkins.createProject(WorkflowJob.class, "p");
+            p.setDefinition(new CpsFlowDefinition(
+                "node() {\n" +
+                "  checkout([$class: 'InvalidChangelogSCM'])\n" +
+                "}", true));
+            r.buildAndAssertSuccess(p);
+        });
+    }
+
     private static void assertPolling(WorkflowJob p, PollingResult.Change expectedChange) {
         assertEquals(expectedChange, p.poll(StreamTaskListener.fromStdout()).change);
     }
 
+    public static class InvalidChangelogSCM extends NullSCM {
+        @DataBoundConstructor
+        public InvalidChangelogSCM() { }
+        @Override public void checkout(Run<?,?> build, Launcher launcher, FilePath workspace, TaskListener listener, File changelogFile, SCMRevisionState baseline) throws IOException, InterruptedException {
+            // Unlike the superclass, which adds an XML header to the file, we just ignore the file.
+        }
+        @Override public ChangeLogParser createChangeLogParser() {
+            return new ChangeLogParser() {
+                public ChangeLogSet<? extends ChangeLogSet.Entry> parse(Run build, RepositoryBrowser<?> browser, File changelogFile) throws IOException, SAXException {
+                    Jenkins.XSTREAM2.fromXML(changelogFile);
+                    throw new AssertionError("The previous line should always fail because the file is empty");
+                }
+            };
+        }
+        @TestExtension("scmParsesUmodifiedChangelogFile")
+        public static class DescriptorImpl extends NullSCM.DescriptorImpl { }
+    }
+
 }