Skip the method PluginsTab::performApply until after activation

If this method (or part of it) is run before the tab has been activated
then the default configuration passed as parameter will be modified and
incorrect values will be introduced.

This commit fixes a regression introduced in
98a5865

Fixes eclipse-pde#1250

org.eclipse.pde.doc.user/forceQualifierUpdate.txt

@@ -1,3 +1,2 @@
 Comparator Errors in 4.32 I-Build I20240304-0140
-Update to IPDELauncherConstants
-https://github.com/eclipse-pde/eclipse.pde/issues/1250
+Update to IPDELauncherConstants

ui/org.eclipse.pde.ui/src/org/eclipse/pde/ui/launcher/PluginsTab.java

@@ -59,6 +59,7 @@ public class PluginsTab extends AbstractLauncherTab {
 	private Combo fDefaultAutoStart;
 	private Spinner fDefaultStartLevel;
 	private final Listener fListener;
+	private boolean fActivated;
 
 	private static final int DEFAULT_SELECTION = 0;
 	private static final int PLUGIN_SELECTION = 1;
@@ -156,6 +157,16 @@ public void createControl(Composite parent) {
 
 	@Override
 	public void initializeFrom(ILaunchConfiguration configuration) {
+		// Long-running initialization happens on first activation of this tab
+	}
+
+	@Override
+	public void activated(ILaunchConfigurationWorkingCopy configuration) {
+		if (fActivated) {
+			// Since this method can be expensive, only activate this tab once.
+			return;
+		}
+
 		try {
 			int index = DEFAULT_SELECTION;
 			if (configuration.getAttribute(IPDELauncherConstants.USE_CUSTOM_FEATURES, false)) {
@@ -171,6 +182,9 @@ public void initializeFrom(ILaunchConfiguration configuration) {
 			fDefaultAutoStart.setText(Boolean.toString(auto));
 			int level = configuration.getAttribute(IPDELauncherConstants.DEFAULT_START_LEVEL, 4);
 			fDefaultStartLevel.setSelection(level);
+
+			// If everything ran smoothly, this tab is activated
+			fActivated = true;
 		} catch (CoreException e) {
 			PDEPlugin.log(e);
 		}
@@ -185,10 +199,13 @@ public void setDefaults(ILaunchConfigurationWorkingCopy configuration) {
 
 	@Override
 	public void performApply(ILaunchConfigurationWorkingCopy configuration) {
+		if (!fActivated) {
+			return;
+		}
 		int index = fSelectionCombo.getSelectionIndex();
 		configuration.setAttribute(IPDELauncherConstants.USE_DEFAULT, index == DEFAULT_SELECTION);
 		configuration.setAttribute(IPDELauncherConstants.USE_CUSTOM_FEATURES, index == FEATURE_SELECTION);
-		fBlock.performApply(configuration);
+			fBlock.performApply(configuration);
 		// clear default values for auto-start and start-level if default
 		String autoText = fDefaultAutoStart.getText();
 		if (Boolean.toString(false).equals(autoText)) {
@@ -217,16 +234,9 @@ public Image getImage() {
 		return fImage;
 	}
 
-	/**
-	 * Validates the tab.  If the feature option is chosen, and the workspace is not correctly set up,
-	 * the error message is set.
-	 *
-	 * @see org.eclipse.pde.ui.launcher.AbstractLauncherTab#validateTab()
-	 */
 	@Override
 	public void validateTab() {
-		String errorMessage = null;
-		setErrorMessage(errorMessage);
+		setErrorMessage(null);
 	}
 
 	@Override