Add support for nested problems display for hierarchical projects

Currently if one select in Project Explorer to display projects not only
flat but hierarchical and choose the "Problems on selected Project"
filtering (but other filters are affected as well) the following
happens:

- We have Project P with nested projects X, Y, Z
- Y has a compile problem and X has warnings
- Now P shows a red icon because it has problems of type error inherited
- I select P but Problems View remains empty
- One has to first expand P, then locate Y and select it
- To see the warning I have to locate X and select it

so there is an inconsistency (P shows problems icon but problems view is
empty) and an inconvenience (I need to select individual childs to see
all problems/warnings).

This now enhances the ExtendedMarkersView by a method
isProjectNestingActive (returns false by default) to allow view
extensions to decide if they want to enable discovery of nested projects
or not. The ProblemsView is further enhanced to detect the situation and
returns true for this particular case.

Author: laeubi

bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/views/markers/ExtendedMarkersView.java

@@ -24,11 +24,14 @@
 import java.util.Collection;
 import java.util.HashSet;
 import java.util.Iterator;
+import java.util.LinkedHashSet;
 import java.util.List;
+import java.util.Set;
 
 import org.eclipse.core.commands.operations.IUndoContext;
 import org.eclipse.core.resources.IFile;
 import org.eclipse.core.resources.IMarker;
+import org.eclipse.core.resources.IProject;
 import org.eclipse.core.resources.ResourcesPlugin;
 import org.eclipse.core.runtime.Adapters;
 import org.eclipse.core.runtime.Assert;
@@ -1642,16 +1645,35 @@ public void selectionChanged(IWorkbenchPart part, ISelection selection) {
 			}
 			// try to adapt them in resources and add it to the
 			// selectedElements
-			List<Object> selectedElements = new ArrayList<>();
+			Set<Object> selectedElements = new LinkedHashSet<>();
 			for (Object object : objectsToAdapt) {
 				Object resElement = MarkerResourceUtil.adapt2ResourceElement(object);
 				if (resElement != null) {
 					selectedElements.add(resElement);
 				}
 			}
+			if (isProjectNestingActive(part)) {
+				List<IProject> selectedProjects = selectedElements.stream().filter(IProject.class::isInstance)
+						.map(IProject.class::cast).toList();
+				if (!selectedProjects.isEmpty()) {
+					selectedElements.addAll(MarkerResourceUtil.getNestedChildProjects(selectedProjects));
+				}
+			}
 			MarkerContentGenerator gen = view.getGenerator();
 			gen.updateSelectedResource(selectedElements.toArray(), part == null);
 		}
+
+	}
+
+	/**
+	 * Check if project nesting is active for this marker view
+	 *
+	 * @param part the currently selected part
+	 * @return <code>true</code> if nesting should be performed, <code>false</code>
+	 *         otherwise
+	 */
+	protected boolean isProjectNestingActive(IWorkbenchPart part) {
+		return false;
 	}
 
 	/**

bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/views/markers/MarkerResourceUtil.java

@@ -31,6 +31,7 @@
 import org.eclipse.core.runtime.Adapters;
 import org.eclipse.core.runtime.CoreException;
 import org.eclipse.core.runtime.IAdaptable;
+import org.eclipse.core.runtime.IPath;
 import org.eclipse.core.runtime.NullProgressMonitor;
 import org.eclipse.ui.internal.ide.Policy;
 import org.eclipse.ui.internal.util.Util;
@@ -286,6 +287,45 @@ static Collection<IProject> getProjectsAsCollection(Object[] elements) {
 		return projects;
 	}
 
+	/**
+	 * Returns all nested child projects of the given projects. A project is
+	 * considered a nested child if its location is a descendant of the parent
+	 * project's location. This supports the hierarchical project display feature.
+	 *
+	 * @param parentProjects
+	 *            the projects to find nested children for
+	 * @return collection of all nested child projects (does not include the parent
+	 *         projects themselves)
+	 */
+	static Collection<IProject> getNestedChildProjects(Collection<IProject> parentProjects) {
+		if (parentProjects == null || parentProjects.isEmpty()) {
+			return Set.of();
+		}
+		Set<IProject> nestedChildren = new HashSet<>();
+
+		for (IProject project : ResourcesPlugin.getWorkspace().getRoot().getProjects()) {
+			if (!project.exists() || !project.isAccessible()) {
+				continue;
+			}
+			IPath projectLocation = project.getLocation();
+			if (projectLocation == null) {
+				continue;
+			}
+			// Check if this project is nested under any of the parent projects
+			for (IProject parentProject : parentProjects) {
+				if (parentProject.equals(project)) {
+					continue; // Skip the project itself
+				}
+				IPath parentLocation = parentProject.getLocation();
+				if (parentLocation != null && parentLocation.isPrefixOf(projectLocation)) {
+					nestedChildren.add(project);
+					break;
+				}
+			}
+		}
+		return nestedChildren;
+	}
+
 	/**
 	 * Add the resources in resourceMapping to the resourceCollection
 	 */

bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/views/markers/ProblemsView.java

@@ -17,9 +17,11 @@
 import org.eclipse.core.resources.IMarker;
 import org.eclipse.core.runtime.Assert;
 import org.eclipse.swt.graphics.Image;
+import org.eclipse.ui.IWorkbenchPart;
 import org.eclipse.ui.ide.undo.WorkspaceUndoUtil;
 import org.eclipse.ui.internal.WorkbenchPlugin;
 import org.eclipse.ui.internal.ide.IDEInternalWorkbenchImages;
+import org.eclipse.ui.navigator.CommonNavigator;
 import org.eclipse.ui.views.markers.MarkerSupportView;
 import org.eclipse.ui.views.markers.internal.MarkerMessages;
 import org.eclipse.ui.views.markers.internal.MarkerSupportRegistry;
@@ -64,4 +66,14 @@ protected String getDeleteOperationName(IMarker[] markers) {
 		return markers.length == 1 ? MarkerMessages.deleteProblemMarker_operationName : MarkerMessages.deleteProblemMarkers_operationName;
 	}
 
+	@Override
+	protected boolean isProjectNestingActive(IWorkbenchPart part) {
+		if (part instanceof CommonNavigator navigator) {
+			return navigator.getNavigatorContentService().getActivationService().isNavigatorExtensionActive(
+					"org.eclipse.ui.navigator.resources.nested.nestedProjectContentProvider"); //$NON-NLS-1$
+
+		}
+		return false;
+	}
+
 }