Add a Themes submenu to Window > Appearance

bundles/org.eclipse.ui.ide/plugin.properties

@@ -343,6 +343,8 @@ multiFilterProvider.description = Match many attributes of files and folders
 menu.window.appearance.label=Appearance
 menu.window.appearance.mnemonic=a
 menu.window.appearance.tooltip=Change appearance of Windows and Toolbars
+menu.window.appearance.themes.label=Themes
+menu.window.appearance.themes.mnemonic=T
 
 menu.copyDetails.label=Cop&y Details
 command.edit.copy.mnemonic = C

bundles/org.eclipse.ui.ide/plugin.xml

@@ -1794,6 +1794,19 @@
                   commandId="org.eclipse.ui.window.minimizePart"
                   style="push">
             </command>
+            <separator
+                  name="org.eclipse.ui.window.appearance.themesSeparator"
+                  visible="true">
+            </separator>
+            <menu
+                  id="org.eclipse.ui.appearance.themes"
+                  label="%menu.window.appearance.themes.label"
+                  mnemonic="%menu.window.appearance.themes.mnemonic">
+               <dynamic
+                     class="org.eclipse.ui.ExtensionFactory:themeContribution"
+                     id="org.eclipse.ui.menus.dynamicThemeMenu">
+               </dynamic>
+            </menu>
          </menu>
       </menuContribution>
 

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

@@ -30,6 +30,7 @@
 import org.eclipse.ui.internal.dialogs.WorkbenchPreferencePage;
 import org.eclipse.ui.internal.keys.KeysPreferencePage;
 import org.eclipse.ui.internal.keys.NewKeysPreferencePage;
+import org.eclipse.ui.internal.menus.ThemeContributionItem;
 import org.eclipse.ui.internal.progress.ProgressView;
 import org.eclipse.ui.internal.themes.ColorsAndFontsPreferencePage;
 import org.eclipse.ui.internal.wizards.preferences.PreferencesExportWizard;
@@ -120,6 +121,12 @@ public class ExtensionFactory implements IExecutableExtensionFactory, IExecutabl
 	 */
 	public static final String SHOW_IN_CONTRIBUTION = "showInContribution"; //$NON-NLS-1$
 
+	/**
+	 * Factory ID for the contribution listing the installed themes. Private on
+	 * purpose, a public constant here would be new API.
+	 */
+	private static final String THEME_CONTRIBUTION = "themeContribution"; //$NON-NLS-1$
+
 	private IConfigurationElement config;
 
 	private String id;
@@ -188,6 +195,9 @@ public Object create() throws CoreException {
 		if (SHOW_IN_CONTRIBUTION.equals(id)) {
 			return new ShowInMenu();
 		}
+		if (THEME_CONTRIBUTION.equals(id)) {
+			return new ThemeContributionItem();
+		}
 
 		throw new CoreException(new Status(IStatus.ERROR, PlatformUI.PLUGIN_ID, 0,
 				"Unknown id in data argument for " + getClass(), null)); //$NON-NLS-1$

bundles/org.eclipse.ui.workbench/eclipseui/org/eclipse/ui/internal/menus/ThemeContributionItem.java

@@ -0,0 +1,121 @@
+/*******************************************************************************
+ * Copyright (c) 2026 vogella GmbH and others.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Lars Vogel <Lars.Vogel@vogella.com> - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.ui.internal.menus;
+
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+
+import org.eclipse.e4.ui.css.swt.theme.ITheme;
+import org.eclipse.e4.ui.css.swt.theme.IThemeEngine;
+import org.eclipse.jface.action.ContributionItem;
+import org.eclipse.jface.action.IContributionItem;
+import org.eclipse.jface.action.Separator;
+import org.eclipse.jface.dialogs.MessageDialog;
+import org.eclipse.swt.SWT;
+import org.eclipse.swt.widgets.Display;
+import org.eclipse.swt.widgets.Menu;
+import org.eclipse.swt.widgets.MenuItem;
+import org.eclipse.ui.PlatformUI;
+import org.eclipse.ui.actions.CompoundContributionItem;
+import org.eclipse.ui.internal.WorkbenchMessages;
+import org.eclipse.ui.internal.themes.DefaultThemePreference;
+
+/**
+ * Lists the installed themes and applies the one the user picks, remembering it
+ * for the next start. A last entry records the active theme as the default for
+ * new workspaces.
+ */
+public class ThemeContributionItem extends CompoundContributionItem {
+
+	public ThemeContributionItem() {
+	}
+
+	public ThemeContributionItem(String id) {
+		super(id);
+	}
+
+	@Override
+	protected IContributionItem[] getContributionItems() {
+		IThemeEngine engine = PlatformUI.getWorkbench().getService(IThemeEngine.class);
+		// High contrast mode pins the engine to the high contrast theme, so offer no choice.
+		if (engine == null || PlatformUI.getWorkbench().getDisplay().getHighContrast()) {
+			return new IContributionItem[0];
+		}
+		List<ITheme> themes = new ArrayList<>(engine.getThemes());
+		themes.sort(Comparator.comparing(ITheme::getLabel, String.CASE_INSENSITIVE_ORDER));
+
+		List<IContributionItem> items = new ArrayList<>();
+		themes.forEach(theme -> items.add(createItem(engine, theme)));
+		if (engine.getActiveTheme() != null) {
+			items.add(new Separator());
+			items.add(createSetAsDefaultItem(engine));
+		}
+		return items.toArray(IContributionItem[]::new);
+	}
+
+	/** Records the active theme as the default for new workspaces. */
+	private static IContributionItem createSetAsDefaultItem(IThemeEngine engine) {
+		return new ContributionItem() {
+			@Override
+			public void fill(Menu menu, int index) {
+				MenuItem item = new MenuItem(menu, SWT.PUSH, index);
+				item.setText(WorkbenchMessages.ThemeDefault_setDefault);
+				item.addListener(SWT.Selection, event -> {
+					ITheme activeTheme = engine.getActiveTheme();
+					if (activeTheme != null) {
+						DefaultThemePreference.set(activeTheme);
+					}
+				});
+			}
+		};
+	}
+
+	private static IContributionItem createItem(IThemeEngine engine, ITheme theme) {
+		return new ContributionItem() {
+			@Override
+			public void fill(Menu menu, int index) {
+				MenuItem item = new MenuItem(menu, SWT.RADIO, index);
+				item.setText(theme.getLabel());
+				ITheme activeTheme = engine.getActiveTheme();
+				item.setSelection(activeTheme != null && activeTheme.getId().equals(theme.getId()));
+				item.addListener(SWT.Selection, event -> {
+					if (!((MenuItem) event.widget).getSelection()) {
+						return;
+					}
+					ITheme previousTheme = engine.getActiveTheme();
+					// Clicking the checked entry fires a selection too, reapplying it would
+					// restyle the whole workbench for nothing.
+					if (previousTheme != null && previousTheme.getId().equals(theme.getId())) {
+						return;
+					}
+					engine.setTheme(theme, true);
+					// Only a light/dark switch leaves parts styled for the previous appearance.
+					if (previousTheme != null && previousTheme.isDark() != theme.isDark()) {
+						offerRestart();
+					}
+				});
+			}
+		};
+	}
+
+	private static void offerRestart() {
+		MessageDialog dialog = new MessageDialog(null, WorkbenchMessages.ThemeChangeWarningTitle, null,
+				WorkbenchMessages.ThemeChangeWarningText, MessageDialog.NONE, 1,
+				WorkbenchMessages.Workbench_RestartButton, WorkbenchMessages.Workbench_DontRestartButton);
+		if (dialog.open() == 0) {
+			Display.getDefault().asyncExec(() -> PlatformUI.getWorkbench().restart());
+		}
+	}
+}