Fix disabled wizard buttons appearing enabled in dark theme

In the dark theme, the CSS sets a foreground color on all Button elements,
which overrides the native OS disabled button rendering. This causes
disabled buttons (like 'Finish') to look identical to enabled ones.

Fix this by setting a 'disabled' CSS class on wizard buttons when they
are disabled. The dark theme CSS now includes a Button.disabled rule
with a dimmed foreground color. A reskin is triggered on state change
so the CSS engine re-applies styles without needing the global
dynamic CSS pseudo-class support (which is disabled for performance).

Author: vogella

bundles/org.eclipse.jface/src/org/eclipse/jface/wizard/WizardDialog.java

@@ -973,7 +973,7 @@ private void restoreEnableState(Control control, Map<String,Object> saveState, S
 		if (control != null) {
 			Boolean b = (Boolean) saveState.get(key);
 			if (b != null) {
-				control.setEnabled(b.booleanValue());
+				setButtonEnabled(control, b.booleanValue());
 			}
 		}
 	}
@@ -1066,10 +1066,25 @@ public void run(boolean fork, boolean cancelable, IRunnableWithProgress runnable
 	private void saveEnableStateAndSet(Control control, Map<String, Object> saveState, String key, boolean enabled) {
 		if (control != null) {
 			saveState.put(key, control.getEnabled() ? Boolean.TRUE : Boolean.FALSE);
-			control.setEnabled(enabled);
+			setButtonEnabled(control, enabled);
 		}
 	}
 
+	/**
+	 * Sets the enabled state of a button and updates the CSS class name so that
+	 * the dark theme can style disabled buttons differently. The CSS class
+	 * "disabled" is set when the button is disabled, and cleared when enabled.
+	 * This triggers a reskin so that the CSS engine re-applies styles.
+	 *
+	 * @param control the button control
+	 * @param enabled whether the button should be enabled
+	 */
+	private static void setButtonEnabled(Control control, boolean enabled) {
+		control.setEnabled(enabled);
+		control.setData("org.eclipse.e4.ui.css.CssClassName", enabled ? null : "disabled"); //$NON-NLS-1$ //$NON-NLS-2$
+		control.reskin(SWT.NONE);
+	}
+
 	/**
 	 * Captures and returns the enabled/disabled state of the wizard dialog's
 	 * buttons and the tree of controls for the currently showing page. All
@@ -1332,13 +1347,13 @@ public void updateButtons() {
 		boolean canFinish = wizard.canFinish();
 		if (backButton != null) {
 			boolean backEnabled = currentPage != null && currentPage.getPreviousPage() != null;
-			backButton.setEnabled(backEnabled);
+			setButtonEnabled(backButton, backEnabled);
 		}
 		if (nextButton != null) {
 			canFlipToNextPage = currentPage != null && currentPage.canFlipToNextPage();
-			nextButton.setEnabled(canFlipToNextPage);
+			setButtonEnabled(nextButton, canFlipToNextPage);
 		}
-		finishButton.setEnabled(canFinish);
+		setButtonEnabled(finishButton, canFinish);
 		// finish is default unless it is disabled and next is enabled
 		if (canFlipToNextPage && !canFinish) {
 			getShell().setDefaultButton(nextButton);

bundles/org.eclipse.ui.themes/css/dark/e4-dark_globalstyle.css

@@ -45,6 +45,11 @@ Group > StyledText {
     color:'#org-eclipse-ui-workbench-DARK_FOREGROUND'; 
 }
 
+/* Disabled buttons should appear dimmed to distinguish them from enabled buttons */
+Button.disabled {
+    color: #777777;
+}
+
 /* ############################## Toolbar ############################## */
 /* Ensure that the labels in the tabfolder gets updated
    See Bug 552780