added AbstractBuild.getRootBuild() that matches up with AbstractProject.getRootProject()

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

@@ -24,6 +24,7 @@
 package hudson.matrix;
 
 import hudson.FilePath;
+import hudson.model.AbstractBuild;
 import hudson.slaves.WorkspaceList;
 import hudson.slaves.WorkspaceList.Lease;
 import static hudson.matrix.MatrixConfiguration.useShortWorkspaceName;
@@ -85,6 +86,14 @@ public class MatrixRun extends Build<MatrixConfiguration,MatrixRun> {
         return getParent().getParent().getBuildByNumber(getNumber());
     }
 
+    /**
+     * The same as {@link #getParentBuild()}.
+     */
+    @Override
+    public AbstractBuild<?, ?> getRootBuild() {
+        return getParentBuild();
+    }
+
     @Override
     public String getDisplayName() {
         StaplerRequest req = Stapler.getCurrentRequest();

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

@@ -185,6 +185,24 @@ public abstract class AbstractBuild<P extends AbstractProject<P,R>,R extends Abs
         return builtOn;
     }
 
+    /**
+     * Gets the nearest ancestor {@link AbstractBuild} that belongs to
+     * {@linkplain AbstractProject#getRootProject() the root project of getProject()} that
+     * dominates/governs/encompasses this build.
+     *
+     * <p>
+     * Some projects (such as matrix projects, Maven projects, or promotion processes) form a tree of jobs,
+     * and still in some of them, builds of child projects are related/tied to that of the parent project.
+     * In such a case, this method returns the governing build.
+     *
+     * @return never null. In the worst case the build dominates itself.
+     * @since 1.421
+     * @see AbstractProject#getRootProject()
+     */
+    public AbstractBuild<?,?> getRootBuild() {
+        return this;
+    }
+
     /**
      * Used to render the side panel "Back to project" link.
      *

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

@@ -368,15 +368,24 @@ public abstract class AbstractProject<P extends AbstractProject<P,R>,R extends A
     }
 
     /**
-     * Returns the root project value.
+     * Gets the nearest ancestor {@link TopLevelItem} that's also an {@link AbstractProject}.
      *
-     * @return the root project value.
+     * <p>
+     * Some projects (such as matrix projects, Maven projects, or promotion processes) form a tree of jobs
+     * that acts as a single unit. This method can be used to find the top most dominating job that
+     * covers such a tree.
+     *
+     * @return never null.
+     * @see AbstractBuild#getRootBuild()
      */
-    public AbstractProject getRootProject() {
-        if (this.getParent() instanceof Jenkins) {
+    public AbstractProject<?,?> getRootProject() {
+        if (this instanceof TopLevelItem) {
             return this;
         } else {
-            return ((AbstractProject) this.getParent()).getRootProject();
+            ItemGroup p = this.getParent();
+            if (p instanceof AbstractProject)
+                return ((AbstractProject) p).getRootProject();
+            return this;
         }
     }
 

maven-plugin/src/main/java/hudson/maven/MavenBuild.java

@@ -178,6 +178,14 @@ public class MavenBuild extends AbstractMavenBuild<MavenModule,MavenBuild> {
         return getParent().getParent().getBuildByNumber(getNumber());
     }
 
+    /**
+     * The same as {@link #getParentBuild()}.
+     */
+    @Override
+    public AbstractBuild<?, ?> getRootBuild() {
+        return getParentBuild();
+    }
+
     /**
      * Gets the "governing" {@link MavenModuleSet} that has set
      * the workspace for this build.