Add missing image to shared images and resolve resource leak

Currently, a shared image descriptor for a missing image is provided via
the ImageDescriptor class. But images created for that descriptor still
have to be maintained manually, e.g., by a resource manager or manual
disposal. In some cases, this is not done correctly, leading to
non-disposed resources.

This change adds a shared instance of the missing image that may be
reused wherever needed. It is adopted for placeholders, which by now
created missing images but never cleaned them up. That resource leak is
resolved with the this change.

Author: HeikoKlare

bundles/org.eclipse.ui.workbench/eclipseui/org/eclipse/ui/ISharedImages.java

@@ -834,6 +834,13 @@ public interface ISharedImages {
 	 */
 	String IMG_OBJS_DND_TOFASTVIEW = "IMG_OBJS_DND_TOFASTVIEW"; //$NON-NLS-1$
 
+	/**
+	 * Identifies the default 'missing' image.
+	 *
+	 * @since 3.137
+	 */
+	String IMG_DEF_MISSING = "IMG_DEF_MISSING"; //$NON-NLS-1$
+
 	/**
 	 * Retrieves the specified image from the workbench plugin's image registry.
 	 * Note: The returned <code>Image</code> is managed by the workbench; clients

bundles/org.eclipse.ui.workbench/eclipseui/org/eclipse/ui/internal/WorkbenchImages.java

@@ -117,6 +117,8 @@ private static final void declareImage(String key, String disabledKey, String pa
 	 */
 	@SuppressWarnings("removal")
 	private static final void declareImages() {
+		declareImage(ISharedImages.IMG_DEF_MISSING, ImageDescriptor.getMissingImageDescriptor(), true);
+
 		// Overlays
 		declareImage(ISharedImages.IMG_DEC_FIELD_ERROR, PATH_OVERLAY + "error_ovr.svg", true); //$NON-NLS-1$
 		declareImage(ISharedImages.IMG_DEC_FIELD_WARNING, PATH_OVERLAY + "warning_ovr.svg", true); //$NON-NLS-1$

bundles/org.eclipse.ui.workbench/eclipseui/org/eclipse/ui/internal/WorkbenchPage.java

@@ -144,6 +144,7 @@
 import org.eclipse.ui.ISaveablesSource;
 import org.eclipse.ui.ISelectionListener;
 import org.eclipse.ui.ISelectionService;
+import org.eclipse.ui.ISharedImages;
 import org.eclipse.ui.IShowEditorInput;
 import org.eclipse.ui.ISources;
 import org.eclipse.ui.IViewPart;
@@ -4038,7 +4039,7 @@ private void handleNullRefPlaceHolders(MUIElement element, MWindow refWin) {
 			if (CompatibilityPart.COMPATIBILITY_VIEW_URI.equals(part.getContributionURI())
 					&& part.getIconURI() == null) {
 				part.getTransientData().put(IPresentationEngine.OVERRIDE_ICON_IMAGE_KEY,
-						ImageDescriptor.getMissingImageDescriptor().createImage());
+						ISharedImages.get().getImage(ISharedImages.IMG_DEF_MISSING));
 			}
 		}
 
@@ -4055,7 +4056,7 @@ private void replacePlaceholder(MPlaceholder ph) {
 		MPart part = modelService.createModelElement(MPart.class);
 		part.setElementId(ph.getElementId());
 		part.getTransientData().put(IPresentationEngine.OVERRIDE_ICON_IMAGE_KEY,
-				ImageDescriptor.getMissingImageDescriptor().createImage());
+				ISharedImages.get().getImage(ISharedImages.IMG_DEF_MISSING));
 		String label = (String) ph.getTransientData().get(IWorkbenchConstants.TAG_LABEL);
 		if (label != null) {
 			part.setLabel(label);