Add 'Manage default...' button to theme preference page

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

@@ -51,6 +51,13 @@ public class WorkbenchMessages extends NLS {
 	public static String ThemeChangeWarningText;
 	public static String ThemeChange_useAsDefault;
 	public static String ThemeChangeWarningTitle;
+	public static String ThemeDefault_manageButton;
+	public static String ThemeDefault_dialogTitle;
+	public static String ThemeDefault_description;
+	public static String ThemeDefault_currentDefault;
+	public static String ThemeDefault_noDefault;
+	public static String ThemeDefault_setDefault;
+	public static String ThemeDefault_removeDefault;
 
 	public static String BundleSigningTray_Cant_Find_Service;
 

bundles/org.eclipse.ui.workbench/eclipseui/org/eclipse/ui/internal/dialogs/ViewsPreferencePage.java

@@ -51,6 +51,7 @@
 import org.eclipse.e4.ui.workbench.renderers.swt.CTabRendering;
 import org.eclipse.e4.ui.workbench.renderers.swt.StackRenderer;
 import org.eclipse.jface.dialogs.Dialog;
+import org.eclipse.jface.dialogs.IDialogConstants;
 import org.eclipse.jface.dialogs.MessageDialog;
 import org.eclipse.jface.fieldassist.ControlDecoration;
 import org.eclipse.jface.fieldassist.FieldDecorationRegistry;
@@ -149,7 +150,14 @@ protected Control createContents(Composite parent) {
 
 		new Label(comp, SWT.NONE).setText(WorkbenchMessages.ViewsPreferencePage_Theme);
 
-		themeIdCombo = new ComboViewer(comp, SWT.READ_ONLY);
+		Composite themeComposite = new Composite(comp, SWT.NONE);
+		GridLayout themeLayout = new GridLayout(2, false);
+		themeLayout.marginWidth = 0;
+		themeLayout.marginHeight = 0;
+		themeComposite.setLayout(themeLayout);
+		themeComposite.setLayoutData(new GridData(GridData.FILL_HORIZONTAL));
+
+		themeIdCombo = new ComboViewer(themeComposite, SWT.READ_ONLY);
 		themeIdCombo.setLabelProvider(createTextProvider(element -> ((ITheme) element).getLabel()));
 		themeIdCombo.setContentProvider(ArrayContentProvider.getInstance());
 		themeIdCombo.setInput(engine.getThemes());
@@ -159,6 +167,11 @@ protected Control createContents(Composite parent) {
 			themeIdCombo.setSelection(new StructuredSelection(currentTheme));
 		}
 		themeComboDecorator = new ControlDecoration(themeIdCombo.getCombo(), SWT.TOP | SWT.LEFT);
+
+		Button manageDefaultButton = new Button(themeComposite, SWT.PUSH);
+		manageDefaultButton.setText(WorkbenchMessages.ThemeDefault_manageButton);
+		manageDefaultButton.addSelectionListener(widgetSelectedAdapter(e -> openManageDefaultThemeDialog()));
+
 		themeIdCombo.addSelectionChangedListener(event -> {
 			ITheme selection = getSelectedTheme();
 			if (!selection.equals(currentTheme)) {
@@ -324,6 +337,62 @@ private ITheme getSelectedTheme() {
 		return (ITheme) (themeIdCombo.getStructuredSelection().getFirstElement());
 	}
 
+	private void openManageDefaultThemeDialog() {
+		IEclipsePreferences configNode = ConfigurationScope.INSTANCE.getNode(E4_THEME_EXTENSION_POINT);
+		String currentDefaultId = configNode.get("themeid", null); //$NON-NLS-1$
+
+		String currentDefaultLabel = null;
+		if (currentDefaultId != null) {
+			for (ITheme t : engine.getThemes()) {
+				if (t.getId().equals(currentDefaultId)) {
+					currentDefaultLabel = t.getLabel();
+					break;
+				}
+			}
+			if (currentDefaultLabel == null) {
+				currentDefaultLabel = currentDefaultId;
+			}
+		}
+
+		String message;
+		if (currentDefaultLabel != null) {
+			message = NLS.bind(WorkbenchMessages.ThemeDefault_currentDefault, currentDefaultLabel);
+		} else {
+			message = WorkbenchMessages.ThemeDefault_noDefault;
+		}
+		message = WorkbenchMessages.ThemeDefault_description + "\n\n" + message; //$NON-NLS-1$
+
+		ITheme selectedTheme = getSelectedTheme();
+		List<String> buttonLabels = new ArrayList<>();
+		buttonLabels.add(WorkbenchMessages.ThemeDefault_setDefault);
+		if (currentDefaultId != null) {
+			buttonLabels.add(WorkbenchMessages.ThemeDefault_removeDefault);
+		}
+		buttonLabels.add(IDialogConstants.CLOSE_LABEL);
+
+		MessageDialog dialog = new MessageDialog(getShell(), WorkbenchMessages.ThemeDefault_dialogTitle, null, message,
+				MessageDialog.INFORMATION, 0, buttonLabels.toArray(new String[0]));
+
+		int result = dialog.open();
+		if (result == 0 && selectedTheme != null) {
+			// Set as default
+			configNode.put("themeid", selectedTheme.getId()); //$NON-NLS-1$
+			try {
+				configNode.flush();
+			} catch (BackingStoreException e) {
+				WorkbenchPlugin.log("Failed to set default theme in configuration scope", e); //$NON-NLS-1$
+			}
+		} else if (currentDefaultId != null && result == 1) {
+			// Remove default
+			configNode.remove("themeid"); //$NON-NLS-1$
+			try {
+				configNode.flush();
+			} catch (BackingStoreException e) {
+				WorkbenchPlugin.log("Failed to remove default theme from configuration scope", e); //$NON-NLS-1$
+			}
+		}
+	}
+
 	@Override
 	public void init(IWorkbench workbench) {
 		MApplication application = workbench.getService(MApplication.class);

bundles/org.eclipse.ui.workbench/eclipseui/org/eclipse/ui/internal/messages.properties

@@ -500,6 +500,13 @@ ThemingEnabled = E&nable theming
 ThemeChangeWarningText = Restart to fully apply theme changes
 ThemeChange_useAsDefault = &Use as default theme (only applies to workspaces without a configured theme)
 ThemeChangeWarningTitle = Theme Changed
+ThemeDefault_manageButton = Manage &default...
+ThemeDefault_dialogTitle = Manage Default Theme
+ThemeDefault_description = The default theme is used for new workspaces and workspaces in which no explicit theme has been set.
+ThemeDefault_currentDefault = Current default theme: {0}
+ThemeDefault_noDefault = No default theme configured. The product default will be used.
+ThemeDefault_setDefault = &Set current theme as default
+ThemeDefault_removeDefault = &Remove default
 RescaleAtRuntimeSettingChangeWarningTitle = DPI Setting Changed
 RescaleAtRuntimeSettingChangeWarningText = Restart for the DPI setting changes to take effect
 RescaleAtRuntimeDescription = Activating this option will dynamically scale all windows according to the monitor they are currently in