Revised version of Extension

core/src/main/java/hudson/matrix/DefaultMatrixRunCheckoutStrategyImpl.java

+package hudson.matrix;
+
+import hudson.Extension;
+import hudson.Launcher;
+import hudson.model.BuildListener;
+
+import java.io.IOException;
+
+import org.kohsuke.stapler.DataBoundConstructor;
+
+public class DefaultMatrixRunCheckoutStrategyImpl extends MatrixRunCheckoutStrategy {
+
+    @DataBoundConstructor
+    public DefaultMatrixRunCheckoutStrategyImpl() {
+        }
+
+    @Override
+    protected boolean preCheckout(MatrixRun build, Launcher launcher, BuildListener listener)
+        throws IOException, InterruptedException {
+        return true;
+    }
+
+    @Override
+    protected boolean checkout(MatrixRun build, Launcher launcher, BuildListener listener) throws Exception {
+        return true;
+    }
+
+    @Extension
+    public static class DescriptorImpl extends MatrixRunCheckoutStrategyDescriptor {
+        @Override
+        public String getDisplayName() {
+            return "Classic";
+        }
+    }
+}

core/src/main/java/hudson/matrix/MatrixProject.java

@@ -160,6 +160,8 @@ public class MatrixProject extends AbstractProject<MatrixProject,MatrixBuild> im
 
     private MatrixExecutionStrategy executionStrategy;
 
+    private MatrixRunCheckoutStrategy matrixRunCheckoutStrategy;
+
     /**
      * Custom workspace location for {@link MatrixConfiguration}s.
      * 
@@ -280,6 +282,16 @@ public class MatrixProject extends AbstractProject<MatrixProject,MatrixBuild> im
         save();
     }
 
+    public MatrixRunCheckoutStrategy getMatrixRunCheckoutStrategy() {
+        return matrixRunCheckoutStrategy == null ? new DefaultMatrixRunCheckoutStrategyImpl() : matrixRunCheckoutStrategy;
+    }
+
+    public void setMatrixRunCheckoutStrategy(MatrixRunCheckoutStrategy matrixRunCheckoutStrategy) throws IOException {
+        if (matrixRunCheckoutStrategy ==null)   throw new IllegalArgumentException();
+        this.matrixRunCheckoutStrategy = matrixRunCheckoutStrategy;
+        save();
+    }
+
     /**
      * @deprecated as of 1.456
      *      Use {@link DefaultMatrixExecutionStrategyImpl#isRunSequentially()}.
@@ -763,6 +775,19 @@ public class MatrixProject extends AbstractProject<MatrixProject,MatrixBuild> im
         else
             executionStrategy = req.bindJSON(esd.get(0).clazz,json.getJSONObject("executionStrategy"));
 
+        try {
+            List<MatrixRunCheckoutStrategyDescriptor> mrcsd = MatrixRunCheckoutStrategyDescriptor
+                .all();
+            if (mrcsd.size() > 1)
+                matrixRunCheckoutStrategy = req.bindJSON(MatrixRunCheckoutStrategy.class,
+                    json.getJSONObject("matrixRunCheckoutStrategy"));
+            else
+                matrixRunCheckoutStrategy = req.bindJSON(mrcsd.get(0).clazz,
+                    json.getJSONObject("matrixRunCheckoutStrategy"));
+        } catch (Exception exc) {
+            matrixRunCheckoutStrategy = new DefaultMatrixRunCheckoutStrategyImpl();
+        }
+
         // parse system axes
         DescribableList<Axis,AxisDescriptor> newAxes = new DescribableList<Axis,AxisDescriptor>(this);
         newAxes.rebuildHetero(req, json, Axis.all(),"axis");
@@ -843,6 +868,10 @@ public class MatrixProject extends AbstractProject<MatrixProject,MatrixBuild> im
         public List<MatrixExecutionStrategyDescriptor> getExecutionStrategyDescriptors() {
             return MatrixExecutionStrategyDescriptor.all();
         }
+
+        public List<MatrixRunCheckoutStrategyDescriptor> getMatrixRunCheckoutStrategyDescriptors() {
+            return MatrixRunCheckoutStrategyDescriptor.all();
+        }
     }
 
     private static final Logger LOGGER = Logger.getLogger(MatrixProject.class.getName());

core/src/main/java/hudson/matrix/MatrixRun.java

@@ -25,10 +25,14 @@ package hudson.matrix;
 
 import hudson.EnvVars;
 import hudson.FilePath;
+import hudson.Launcher;
 import hudson.model.AbstractBuild;
+import hudson.model.BuildListener;
+import hudson.model.BuildableItemWithBuildWrappers;
 import hudson.model.TopLevelItem;
 import hudson.slaves.WorkspaceList;
 import hudson.slaves.WorkspaceList.Lease;
+import hudson.tasks.BuildWrapper;
 import hudson.model.Build;
 import hudson.model.Node;
 import org.kohsuke.stapler.Ancestor;
@@ -182,5 +186,24 @@ public class MatrixRun extends Build<MatrixConfiguration,MatrixRun> {
             String childWs = mp.getChildCustomWorkspace();
             return Lease.createLinkedDummyLease(baseDir.child(env.expand(childWs)),baseLease);
         }
+        @Override
+        protected void preCheckout(Launcher launcher, BuildListener listener)
+                throws IOException, InterruptedException {
+            MatrixProject mp = getParent().getParent();
+            MatrixRunCheckoutStrategy strategy = mp.getMatrixRunCheckoutStrategy();
+            boolean invokeSuper = strategy.preCheckout(MatrixRun.this, launcher, listener);
+            if(invokeSuper) {
+                super.preCheckout(launcher, listener);
+            }
+        }
+        @Override
+        protected void checkout(BuildListener listener) throws Exception {
+            MatrixProject mp = getParent().getParent();
+            MatrixRunCheckoutStrategy strategy = mp.getMatrixRunCheckoutStrategy();
+            boolean invokeSuper = strategy.checkout(MatrixRun.this, launcher, listener);
+            if(invokeSuper) {
+                super.checkout(listener);
+            }
+        }
     }
 }

core/src/main/java/hudson/matrix/MatrixRunCheckoutStrategy.java

+package hudson.matrix;
+
+import hudson.ExtensionPoint;
+import hudson.Launcher;
+import hudson.model.AbstractDescribableImpl;
+import hudson.model.BuildListener;
+
+import java.io.IOException;
+
+public abstract class MatrixRunCheckoutStrategy extends
+    AbstractDescribableImpl<MatrixRunCheckoutStrategy> implements ExtensionPoint {
+
+    protected abstract boolean preCheckout(MatrixRun build, Launcher launcher, BuildListener listener) throws IOException, InterruptedException;
+    protected abstract boolean checkout(MatrixRun build, Launcher launcher, BuildListener listener) throws Exception;
+
+    @Override
+    public MatrixRunCheckoutStrategyDescriptor getDescriptor() {
+        return (MatrixRunCheckoutStrategyDescriptor)super.getDescriptor();
+    }
+}

core/src/main/java/hudson/matrix/MatrixRunCheckoutStrategyDescriptor.java

+package hudson.matrix;
+
+import hudson.DescriptorExtensionList;
+import hudson.model.Descriptor;
+import jenkins.model.Jenkins;
+
+public abstract class MatrixRunCheckoutStrategyDescriptor extends Descriptor<MatrixRunCheckoutStrategy> {
+
+    protected MatrixRunCheckoutStrategyDescriptor(Class<? extends MatrixRunCheckoutStrategy> clazz) {
+        super(clazz);
+    }
+
+    protected MatrixRunCheckoutStrategyDescriptor() {
+    }
+
+    /**
+     * Returns all the registered {@link MatrixExecutionStrategyDescriptor}s.
+     */
+    public static DescriptorExtensionList<MatrixRunCheckoutStrategy,MatrixRunCheckoutStrategyDescriptor> all() {
+        return Jenkins.getInstance().<MatrixRunCheckoutStrategy,MatrixRunCheckoutStrategyDescriptor>getDescriptorList(MatrixRunCheckoutStrategy.class);
+    }
+
+}

core/src/main/java/hudson/model/AbstractBuild.java

@@ -568,7 +568,7 @@ public abstract class AbstractBuild<P extends AbstractProject<P,R>,R extends Abs
          * @throws IOException
          * @throws InterruptedException
          */
-        private void preCheckout(Launcher launcher, BuildListener listener) throws IOException, InterruptedException{
+        protected void preCheckout(Launcher launcher, BuildListener listener) throws IOException, InterruptedException{
         	if (project instanceof BuildableItemWithBuildWrappers) {
                 BuildableItemWithBuildWrappers biwbw = (BuildableItemWithBuildWrappers) project;
                 for (BuildWrapper bw : biwbw.getBuildWrappersList())
@@ -576,7 +576,7 @@ public abstract class AbstractBuild<P extends AbstractProject<P,R>,R extends Abs
             }
         }
         
-        private void checkout(BuildListener listener) throws Exception {
+        protected void checkout(BuildListener listener) throws Exception {
                 for (int retryCount=project.getScmCheckoutRetryCount(); ; retryCount--) {
                     // for historical reasons, null in the scm field means CVS, so we need to explicitly set this to something
                     // in case check out fails and leaves a broken changelog.xml behind.

core/src/main/resources/hudson/matrix/DefaultMatrixRunCheckoutStrategyImpl/config.jelly

+<!--
+The MIT License
+
+Copyright (c) 2004-2009, Sun Microsystems, Inc., Kohsuke Kawaguchi
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+-->
+
+<!-- nothing to configure -->
+<?jelly escape-by-default='true'?>
+<j:jelly xmlns:j="jelly:core"/>

core/src/main/resources/hudson/matrix/MatrixProject/configure-entries.jelly

@@ -57,6 +57,18 @@ THE SOFTWARE.
 
   <p:config-scm/>
 
+  <f:section title="${%Advanced Source Code Management}">
+	<j:choose>
+		<j:when test="${descriptor.matrixRunCheckoutStrategyDescriptors.size() gt 1}">
+			<f:dropdownDescriptorSelector title="${%Matrix Run Checkout Strategy}" field="matrixRunCheckoutStrategy"/>
+		</j:when>
+		<j:otherwise>
+			<!-- for the default case when there's only one build checkout strategy, render it inline to simplify the UI -->
+			<f:property field="matrixRunCheckoutStrategy" propertyDescriptor="${descriptor.matrixRunCheckoutStrategyDescriptors.get(0)}"/>
+		</j:otherwise>
+	</j:choose>
+  </f:section>
+
   <p:config-trigger>
     <p:config-upstream-pseudo-trigger />
   </p:config-trigger>