[FIXED JENKINS-16979]

Added backward compatible data loader and a corresponding test case.

changelog.html

@@ -63,6 +63,9 @@ Upcoming changes</a>
 <div id="rc" style="display:none;"><!--=BEGIN=-->
 <h3><a name=v1.504>What's new in 1.504</a> <!--=DATE=--></h3>
 <ul class=image>
+  <li class='major bug'>
+    Fixed a regression in the "discard old builds" in 1.503.
+    (<a href="https://issues.jenkins-ci.org/browse/JENKINS-16979">issue 16979</a>)
   <li class='major bug'>
     Maven 3.0.5 upgrade.
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-16965">issue 16965</a>)

core/src/main/java/jenkins/model/BuildDiscarder.java

 package jenkins.model;
 
+import com.thoughtworks.xstream.converters.Converter;
+import com.thoughtworks.xstream.converters.MarshallingContext;
+import com.thoughtworks.xstream.converters.UnmarshallingContext;
+import com.thoughtworks.xstream.core.JVM;
+import com.thoughtworks.xstream.io.HierarchicalStreamReader;
+import com.thoughtworks.xstream.io.HierarchicalStreamWriter;
+import com.thoughtworks.xstream.mapper.Mapper;
 import hudson.ExtensionPoint;
 import hudson.model.AbstractDescribableImpl;
+import hudson.model.AbstractProject;
 import hudson.model.Job;
 import hudson.model.Run;
+import hudson.tasks.LogRotator;
+import hudson.util.RobustReflectionConverter;
 
 import java.io.IOException;
 
@@ -34,4 +44,38 @@ public abstract class BuildDiscarder extends AbstractDescribableImpl<BuildDiscar
     public BuildDiscarderDescriptor getDescriptor() {
         return (BuildDiscarderDescriptor)super.getDescriptor();
     }
+
+    /**
+     * {@link AbstractProject#logRotator} used to be typed as {@link LogRotator},
+     * so such configuration file ends up trying to unmarshal {@link BuildDiscarder} and
+     * not its subtype.
+     *
+     * This converter makes this work by unmarshalling a {@link LogRotator}.
+     */
+    public static class ConverterImpl implements Converter {
+        private RobustReflectionConverter ref;
+
+        public ConverterImpl(Mapper m) {
+            ref = new RobustReflectionConverter(m,new JVM().bestReflectionProvider()) {
+                @Override
+                protected Object instantiateNewInstance(HierarchicalStreamReader reader, UnmarshallingContext context) {
+                    return reflectionProvider.newInstance(LogRotator.class);
+                }
+            };
+        }
+
+        public void marshal(Object source, HierarchicalStreamWriter writer, MarshallingContext context) {
+            // abstract class, so there shouldn't be any instance.
+            throw new UnsupportedOperationException();
+        }
+
+        public Object unmarshal(HierarchicalStreamReader reader, UnmarshallingContext context) {
+            // force unmarshal as LogRotator
+            return ref.unmarshal(reader,context);
+        }
+
+        public boolean canConvert(Class type) {
+            return type==BuildDiscarder.class;
+        }
+    }
 }

test/src/test/groovy/jenkins/model/BuildDiscarderTest.groovy

+package jenkins.model
+
+import hudson.model.AbstractProject
+import hudson.tasks.LogRotator
+import org.jvnet.hudson.test.Bug
+import org.jvnet.hudson.test.HudsonTestCase
+import org.jvnet.hudson.test.recipes.LocalData
+
+import javax.xml.transform.Source
+import javax.xml.transform.stream.StreamSource
+
+
+/**
+ *
+ *
+ * @author Kohsuke Kawaguchi
+ */
+public class BuildDiscarderTest extends HudsonTestCase {
+    @Bug(16979)
+    @LocalData
+    void testCompatibility() {
+        AbstractProject p = jenkins.getItem("foo")
+        verifyLogRotatorSanity(p)
+
+        // now persist in the new format
+        p.save()
+        def xml = p.configFile.asString()
+
+        // make sure this new format roundtrips by itself
+        p.buildDiscarder = null
+        p.updateByXml((Source)new StreamSource(new StringReader(xml)))
+        verifyLogRotatorSanity(p)
+
+        // another sanity check
+        assert xml.contains("<logRotator class=\"${LogRotator.class.name}\">")
+    }
+
+    private static void verifyLogRotatorSanity(AbstractProject p) {
+        LogRotator d = p.buildDiscarder
+        assert d.daysToKeep == 4;
+        assert d.numToKeep == 3;
+        assert d.artifactDaysToKeep == 2;
+        assert d.artifactNumToKeep == 1;
+    }
+}
\ No newline at end of file

test/src/test/resources/jenkins/model/BuildDiscarderTest/testCompatibility/config.xml

+<hudson/>

test/src/test/resources/jenkins/model/BuildDiscarderTest/testCompatibility/jobs/foo/config.xml

+<?xml version='1.0' encoding='UTF-8'?>
+<!--
+  Pre 1.503, LogRotator was a concrete class and saved like this
+-->
+<project>
+  <actions/>
+  <description></description>
+  <logRotator>
+    <daysToKeep>4</daysToKeep>
+    <numToKeep>3</numToKeep>
+    <artifactDaysToKeep>2</artifactDaysToKeep>
+    <artifactNumToKeep>1</artifactNumToKeep>
+  </logRotator>
+  <keepDependencies>false</keepDependencies>
+  <properties/>
+  <scm class="hudson.scm.NullSCM"/>
+  <canRoam>true</canRoam>
+  <disabled>false</disabled>
+  <blockBuildWhenDownstreamBuilding>false</blockBuildWhenDownstreamBuilding>
+  <blockBuildWhenUpstreamBuilding>false</blockBuildWhenUpstreamBuilding>
+  <triggers class="vector"/>
+  <concurrentBuild>false</concurrentBuild>
+  <builders/>
+  <publishers/>
+  <buildWrappers/>
+</project>