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

Adds a button next to the theme selection combo box that opens a dialog
allowing users to set the currently selected theme as the default for new
workspaces or remove an existing default. The dialog explains that the
default theme applies to new workspaces and workspaces without an
explicit theme, and shows the current default if one is configured.

Author: vogella

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