Style CTabFolder pages that are hidden when they are skinned

bundles/org.eclipse.e4.ui.css.swt/src/org/eclipse/e4/ui/css/swt/engine/CSSSWTApplyStylesListener.java

@@ -15,22 +15,69 @@
 
 import org.eclipse.e4.ui.css.core.engine.CSSEngine;
 import org.eclipse.swt.SWT;
+import org.eclipse.swt.custom.CTabFolder;
+import org.eclipse.swt.widgets.Control;
 import org.eclipse.swt.widgets.Display;
+import org.eclipse.swt.widgets.Event;
+import org.eclipse.swt.widgets.Listener;
 
 
 /**
- * Add SWT filter to the {@link Display} to apply styles when SWT widget is
- * resized or showed.
+ * Applies styles to the widgets of a {@link Display} when they are skinned, and
+ * to a {@link CTabFolder} page the engine skipped once it becomes the selected tab's page.
  */
 public class CSSSWTApplyStylesListener {
+	// marks a control this listener already watches, since every re-skin repeats the skin event
+	private final String pendingPageKey = getClass().getName() + '@' + Integer.toHexString(hashCode());
+
 	CSSEngine engine;
 	public CSSSWTApplyStylesListener(Display display, final CSSEngine engine) {
 		this.engine = engine;
 		display.addListener(SWT.Skin, event -> {
-			if (engine != null) {
-				engine.applyStyles(event.widget, false);
+			if (engine == null) {
+				return;
+			}
+			engine.applyStyles(event.widget, false);
+			if (event.widget instanceof Control control && control.getParent() instanceof CTabFolder folder
+					&& control != folder.getTopRight() && !isPageOfSelectedTab(folder, control)) {
+				// the folder hides this page from the engine, so it was skipped
+				styleWhenItBecomesThePage(folder, control);
 			}
 		});
 	}
 
+	/**
+	 * Styles the control once it is the selected tab's page, which attaching it
+	 * resizes it to or selecting its tab shows it.
+	 */
+	private void styleWhenItBecomesThePage(CTabFolder folder, Control control) {
+		if (control.getData(pendingPageKey) != null) {
+			return;
+		}
+		Listener listener = new Listener() {
+			@Override
+			public void handleEvent(Event event) {
+				// the control may have been reparented, and a new skin event watches it again
+				boolean inFolder = control.getParent() == folder && !folder.isDisposed();
+				if (inFolder && !isPageOfSelectedTab(folder, control)) {
+					return;
+				}
+				control.removeListener(SWT.Show, this);
+				control.removeListener(SWT.Resize, this);
+				control.setData(pendingPageKey, null);
+				if (inFolder) {
+					engine.applyStyles(control, true);
+				}
+			}
+		};
+		control.setData(pendingPageKey, listener);
+		control.addListener(SWT.Show, listener);
+		control.addListener(SWT.Resize, listener);
+	}
+
+	private static boolean isPageOfSelectedTab(CTabFolder folder, Control control) {
+		int selected = folder.getSelectionIndex();
+		return selected >= 0 && folder.getItem(selected).getControl() == control;
+	}
+
 }

tests/org.eclipse.e4.ui.tests.css.swt/src/org/eclipse/e4/ui/tests/css/swt/CTabFolderTest.java

@@ -22,8 +22,12 @@
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotSame;
 
+import java.io.IOException;
+import java.io.StringReader;
+
 import org.eclipse.e4.ui.css.core.engine.CSSEngine;
 import org.eclipse.e4.ui.css.swt.dom.WidgetElement;
+import org.eclipse.e4.ui.css.swt.engine.CSSSWTEngineImpl;
 import org.eclipse.swt.SWT;
 import org.eclipse.swt.custom.CTabFolder;
 import org.eclipse.swt.custom.CTabItem;
@@ -356,4 +360,68 @@ void testMinimumCharacters() {
 		assertEquals(1, folderToTest.getMinimumCharacters());
 		assertEquals("1", css.getEngine().retrieveCSSProperty(folderToTest, "swt-tab-text-minimum-characters", null));
 	}
+
+	@Test
+	void testPageSelectedProgrammaticallyAfterSkinningIsStyled() throws IOException {
+		Display display = css.getDisplay();
+		CSSEngine engine = new CSSSWTEngineImpl(display, true);
+		// a class selector keeps this engine, which stays attached to the shared
+		// display as a skin listener, from styling the widgets of other tests
+		engine.parseStyleSheet(new StringReader(".tabPage { background-color: #FF0000 }"));
+
+		Shell shell = new Shell(display, SWT.SHELL_TRIM);
+		shell.setLayout(new FillLayout());
+		CTabFolder folderToTest = new CTabFolder(shell, SWT.NONE);
+		CTabItem tab1 = new CTabItem(folderToTest, SWT.NONE);
+		tab1.setText("A TAB ITEM");
+		// nothing is selected yet, so the page is hidden and the CTabFolder does
+		// not expose it to the engine
+		Composite page = new Composite(folderToTest, SWT.NONE);
+		WidgetElement.setCSSClass(page, "tabPage");
+		tab1.setControl(page);
+		spinEventLoop(display); // the skin pass skips the hidden page
+
+		// a programmatic selection sends no selection event, so only the page
+		// becoming visible can trigger its styling
+		folderToTest.setSelection(0);
+		spinEventLoop(display);
+
+		assertEquals(RED, page.getBackground().getRGB());
+	}
+
+	@Test
+	void testPageAttachedToItsItemAfterSkinningIsStyled() throws IOException {
+		Display display = css.getDisplay();
+		CSSEngine engine = new CSSSWTEngineImpl(display, true);
+		engine.parseStyleSheet(new StringReader(".tabPage { background-color: #FF0000 }"));
+
+		Shell shell = new Shell(display, SWT.SHELL_TRIM);
+		shell.setLayout(new FillLayout());
+		CTabFolder folderToTest = new CTabFolder(shell, SWT.NONE);
+		CTabItem tab1 = new CTabItem(folderToTest, SWT.NONE);
+		tab1.setText("A TAB ITEM");
+		folderToTest.setSelection(0);
+		shell.setSize(400, 300);
+		shell.layout(true, true);
+
+		Composite page = new Composite(folderToTest, SWT.NONE);
+		WidgetElement.setCSSClass(page, "tabPage");
+		// building the page runs the event loop, as loading a search page does in
+		// the Search dialog, so the page is skinned while its item has no control
+		// yet and the CTabFolder does not expose it
+		spinEventLoop(display);
+
+		// the tab is already selected and the page has been visible since it was
+		// created, so attaching it sends no show event either
+		tab1.setControl(page);
+		spinEventLoop(display);
+
+		assertEquals(RED, page.getBackground().getRGB());
+	}
+
+	private static void spinEventLoop(Display display) {
+		while (display.readAndDispatch()) {
+			// deliver the pending skin and show events
+		}
+	}
 }