Allow user to set default theme

During theme switch the user can now set the selected theme as default.
This setting is saved as configuration scope and loaded for new
workspaces unless the user has a theme set for this specific workspace.
Adds 'Use as default theme' checkbox to the theme restart dialog.

Author: vogella

bundles/org.eclipse.e4.ui.css.swt.theme/src/org/eclipse/e4/ui/css/swt/internal/theme/ThemeEngine.java

@@ -41,6 +41,7 @@
 import org.eclipse.core.runtime.Platform;
 import org.eclipse.core.runtime.RegistryFactory;
 import org.eclipse.core.runtime.preferences.IEclipsePreferences;
+import org.eclipse.core.runtime.preferences.IPreferencesService;
 import org.eclipse.core.runtime.preferences.InstanceScope;
 import org.eclipse.e4.ui.css.core.engine.CSSElementContext;
 import org.eclipse.e4.ui.css.core.engine.CSSEngine;
@@ -86,6 +87,8 @@ public class ThemeEngine implements IThemeEngine {
 
 	public static final String E4_DARK_THEME_ID = "org.eclipse.e4.ui.css.theme.e4_dark";
 
+	public static final String E4_DEFAULT_THEME_ID = "org.eclipse.e4.ui.css.theme.e4_default";
+
 	public static final String DISABLE_OS_DARK_THEME_INHERIT = "org.eclipse.e4.ui.css.theme.disableOSDarkThemeInherit";
 
 	public ThemeEngine(Display display) {
@@ -424,9 +427,15 @@ public void setTheme(String themeId, boolean restore) {
 		for (Theme t : themes) {
 			if (t.getId().equals(themeId)) {
 				setTheme(t, restore);
-				break;
+				return;
 			}
 		}
+		// Theme not found (e.g. it was uninstalled); fall back to default
+		Platform.getLog(ThemeEngine.class)
+				.warn("Theme '" + themeId + "' not found; falling back to default theme."); //$NON-NLS-1$ //$NON-NLS-2$
+		if (!E4_DEFAULT_THEME_ID.equals(themeId)) {
+			setTheme(E4_DEFAULT_THEME_ID, restore);
+		}
 	}
 
 	@Override
@@ -556,7 +565,8 @@ public void applyStyles(Object widget, boolean applyStylesToChildNodes) {
 	}
 
 	private String getPreferenceThemeId() {
-		return getPreferences().get(THEMEID_KEY, null);
+		IPreferencesService prefService = Platform.getPreferencesService();
+		return prefService.getString(THEME_PLUGIN_ID, THEMEID_KEY, null, null);
 	}
 
 	private IEclipsePreferences getPreferences() {

bundles/org.eclipse.e4.ui.workbench.swt/src/org/eclipse/e4/ui/internal/workbench/swt/E4Application.java

@@ -38,6 +38,8 @@
 import org.eclipse.core.runtime.IProduct;
 import org.eclipse.core.runtime.Platform;
 import org.eclipse.core.runtime.RegistryFactory;
+import org.eclipse.core.runtime.preferences.ConfigurationScope;
+import org.eclipse.core.runtime.preferences.IEclipsePreferences;
 import org.eclipse.e4.core.contexts.ContextFunction;
 import org.eclipse.e4.core.contexts.ContextInjectionFactory;
 import org.eclipse.e4.core.contexts.EclipseContextFactory;
@@ -315,7 +317,10 @@ private void setCSSContextVariables(IApplicationContext applicationContext, IEcl
 				: getArgValue(E4Application.THEME_ID, applicationContext, false);
 
 		if (!themeId.isPresent() && !cssURI.isPresent()) {
-			context.set(E4Application.THEME_ID, DEFAULT_THEME_ID);
+			IEclipsePreferences configurationScopeNode = ConfigurationScope.INSTANCE
+					.getNode("org.eclipse.e4.ui.css.swt.theme");
+			String defaultThemeId = configurationScopeNode.get("themeid", DEFAULT_THEME_ID);
+			context.set(E4Application.THEME_ID, defaultThemeId);
 		} else {
 			context.set(E4Application.THEME_ID, themeId.orElseGet(() -> null));
 		}

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

@@ -49,7 +49,7 @@ public class WorkbenchMessages extends NLS {
 	public static String RescaleAtRuntimeSettingChangeWarningText;
 
 	public static String ThemeChangeWarningText;
-
+	public static String ThemeChange_useAsDefault;
 	public static String ThemeChangeWarningTitle;
 
 	public static String BundleSigningTray_Cant_Find_Service;

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

@@ -20,6 +20,7 @@
 package org.eclipse.ui.internal.dialogs;
 
 import static org.eclipse.jface.viewers.LabelProvider.createTextProvider;
+import static org.eclipse.swt.events.SelectionListener.widgetSelectedAdapter;
 import static org.eclipse.ui.internal.registry.IWorkbenchRegistryConstants.ATT_COLOR_AND_FONT_ID;
 import static org.eclipse.ui.internal.registry.IWorkbenchRegistryConstants.ATT_OS_VERSION;
 import static org.eclipse.ui.internal.registry.IWorkbenchRegistryConstants.ATT_THEME_ASSOCIATION;
@@ -61,7 +62,6 @@
 import org.eclipse.jface.viewers.ISelection;
 import org.eclipse.jface.viewers.LabelProvider;
 import org.eclipse.jface.viewers.StructuredSelection;
-import org.eclipse.jface.window.Window;
 import org.eclipse.osgi.util.NLS;
 import org.eclipse.swt.SWT;
 import org.eclipse.swt.events.SelectionEvent;
@@ -419,16 +419,49 @@ public boolean performOk() {
 		}
 
 		if (showRestartDialog) {
-			showRestartDialog(restartDialogTitle, restartDialogMessage);
+			String themeId = null;
+			if (isThemingPossible()) {
+				ITheme theme = getSelectedTheme();
+				if (theme != null) {
+					themeId = theme.getId();
+				}
+			}
+			showRestartDialog(restartDialogTitle, restartDialogMessage, themeId);
 		}
 
 		return super.performOk();
 	}
 
-	private void showRestartDialog(String title, String warningText) {
-		if (new MessageDialog(null, title, null, warningText, MessageDialog.NONE, 2,
-				WorkbenchMessages.Workbench_RestartButton, WorkbenchMessages.Workbench_DontRestartButton)
-						.open() == Window.OK) {
+	private void showRestartDialog(String title, String warningText, String themeId) {
+		boolean[] useAsDefault = { true };
+		MessageDialog dialog = new MessageDialog(null, title, null, warningText, MessageDialog.NONE, 2,
+				WorkbenchMessages.Workbench_RestartButton, WorkbenchMessages.Workbench_DontRestartButton) {
+			@Override
+			protected Control createCustomArea(Composite parent) {
+				if (themeId == null) {
+					return null;
+				}
+				Button checkbox = new Button(parent, SWT.CHECK);
+				checkbox.setText(WorkbenchMessages.ThemeChange_useAsDefault);
+				checkbox.setSelection(useAsDefault[0]);
+				checkbox.addSelectionListener(widgetSelectedAdapter(e -> useAsDefault[0] = checkbox.getSelection()));
+				return checkbox;
+			}
+		};
+		int result = dialog.open();
+		if (result == 0 || result == 1) { // 0: Restart, 1: Don't Restart
+			if (themeId != null && useAsDefault[0]) {
+				IEclipsePreferences configurationScopeNode = ConfigurationScope.INSTANCE
+						.getNode(E4_THEME_EXTENSION_POINT);
+				configurationScopeNode.put("themeid", themeId); //$NON-NLS-1$
+				try {
+					configurationScopeNode.flush();
+				} catch (BackingStoreException e) {
+					WorkbenchPlugin.log("Failed to set default theme in configuration scope", e); //$NON-NLS-1$
+				}
+			}
+		}
+		if (result == 0) {
 			Display.getDefault().asyncExec(() -> PlatformUI.getWorkbench().restart());
 		}
 	}

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

@@ -498,6 +498,7 @@ PreferencePage_noDescription = (No description available)
 PreferencePageParameterValues_pageLabelSeparator = \ >\ 
 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
 RescaleAtRuntimeSettingChangeWarningTitle = DPI Setting Changed
 RescaleAtRuntimeSettingChangeWarningText = Restart for the DPI setting changes to take effect