Add missing descriptions to Colors and Fonts theme entries

Some Colors and Fonts entries already provide user-facing descriptions
via ThemeElementCategory, while others do not.
This change uses the existing descriptions to display in the description
box and adds description for ones that doesn't have any entries to
ensure the description area is not left empty and that available
descriptions are consistently utilised.
This aligns with the standard usage elsewhere in Eclipse preference
pages.

Author: elsazac

bundles/org.eclipse.ui.workbench/eclipseui/org/eclipse/ui/internal/themes/ColorsAndFontsPreferencePage.java

@@ -1974,6 +1974,17 @@ private void editColor(ColorDefinition definition, Display display) {
 		}
 	}
 
+	private ThemeElementCategory getCategory() {
+		IStructuredSelection item = (IStructuredSelection) tree.getViewer().getSelection();
+		if (item != null && !item.isEmpty()) {
+			Object object = item.getFirstElement();
+			if (object instanceof ThemeElementCategory) {
+				return (ThemeElementCategory) object;
+			}
+		}
+		return null;
+	}
+
 	protected void updateControls() {
 		FontDefinition fontDefinition = getSelectedFontDefinition();
 		if (fontDefinition != null) {
@@ -1999,6 +2010,18 @@ protected void updateControls() {
 			setCurrentColor(colorDefinition);
 			return;
 		}
+		ThemeElementCategory category = getCategory();
+		if (category != null) {
+			fontChangeButton.setEnabled(false);
+			fontSystemButton.setEnabled(false);
+			fontResetButton.setEnabled(false);
+			editDefaultButton.setEnabled(false);
+			goToDefaultButton.setEnabled(false);
+
+			String desc = category.getDescription() != null ? category.getDescription() : ""; //$NON-NLS-1$
+			descriptionText.setText(desc);
+			return;
+		}
 		// not a font or a color?
 		fontChangeButton.setEnabled(false);
 		fontSystemButton.setEnabled(false);

examples/org.eclipse.e4.demo.cssbridge/plugin.properties

@@ -19,6 +19,8 @@ org.eclipse.e4.demo.cssbridge.blue.theme=Blue theme
 org.eclipse.e4.demo.cssbridge.green.theme=Green theme
 org.eclipse.e4.demo.cssbridge.red.theme=Red theme
 
+org.eclipse.e4.demo.cssbridge.ui.views.Theme.description= Colors and fonts used to demonstrate CSS based UI styling.
+
 org.eclipse.e4.demo.cssbridge.ui.views.Theme=CSS bridge demo theme
 org.eclipse.e4.demo.cssbridge.ui.views.theme.shell.background=Shell background
 org.eclipse.e4.demo.cssbridge.ui.views.theme.shell.selection.foreground=Shell selection foreground

examples/org.eclipse.e4.demo.cssbridge/plugin.xml

@@ -109,10 +109,14 @@
 
    <!-- The 3.x theme definition -->
    <extension point="org.eclipse.ui.themes">
-      <themeElementCategory
-            id="org.eclipse.e4.demo.cssbridge.ui.views.Theme"
-            label="%org.eclipse.e4.demo.cssbridge.ui.views.Theme"/>
-
+   <themeElementCategory
+         id="org.eclipse.e4.demo.cssbridge.ui.views.Theme"
+         label="%org.eclipse.e4.demo.cssbridge.ui.views.Theme">
+      <description>
+         %org.eclipse.e4.demo.cssbridge.ui.views.Theme.description
+      </description>
+   </themeElementCategory>
+   
       <!-- for IDs see the class: org.eclipse.e4.demo.cssbridge.ui.views.Shell -->
       <colorDefinition
         	id="org.eclipse.e4.demo.cssbridge.ui.views.theme.shell.selection.foreground"