Activate the current tab when switching between run configurations

Make sure that the selected tab is activated (i.e. that its "activate"
method is called) when switching between existing run configurations in
the "Run configurations" dialog.

Contributes to eclipse-pde/eclipse.pde#674

debug/org.eclipse.debug.ui/ui/org/eclipse/debug/internal/ui/launchConfigurations/LaunchConfigurationTabGroupViewer.java

@@ -842,8 +842,9 @@ protected void displayInstanceTabs(boolean redrawTabs) {
 			fInitializingTabs = false;
 			return;
 		}
+		Class<? extends ILaunchConfigurationTab> lastActiveTabKind = null;
 		if(redrawTabs) {
-			showInstanceTabsFor(type);
+			lastActiveTabKind = showInstanceTabsFor(type);
 		}
 		// show the name area
 		updateVisibleControls(true);
@@ -875,17 +876,25 @@ protected void displayInstanceTabs(boolean redrawTabs) {
 		// Turn off initializing flag to update message
 		fInitializingTabs = false;
 
+		// Try to activate the same (type of) tab that was active before.
+		if (!setActiveTab(lastActiveTabKind)) {
+			// The tab with the wanted class wasn't found. Try to activate the first one
+			setActiveTab(0);
+		}
+
 		if (!fViewform.isVisible()) {
 			fViewform.setVisible(true);
 		}
 	}
 
 	/**
-	 * Populate the tabs in the configuration edit area to be appropriate to the current
-	 * launch configuration type.
+	 * Populate the tabs in the configuration edit area to be appropriate to the
+	 * current launch configuration type.
+	 *
 	 * @param configType the type to show tabs for
+	 * @return The class of the last active tab.
 	 */
-	private void showInstanceTabsFor(ILaunchConfigurationType configType) {
+	private Class<? extends ILaunchConfigurationTab> showInstanceTabsFor(ILaunchConfigurationType configType) {
 		// try to keep on same tab
 		Class<? extends ILaunchConfigurationTab> tabKind = null;
 		if (getActiveTab() != null) {
@@ -897,7 +906,7 @@ private void showInstanceTabsFor(ILaunchConfigurationType configType) {
 			group = createGroup();
 		} catch (CoreException ce) {
 			DebugUIPlugin.errorDialog(getShell(), LaunchConfigurationsMessages.LaunchConfigurationDialog_Error_19, LaunchConfigurationsMessages.LaunchConfigurationDialog_Exception_occurred_creating_launch_configuration_tabs_27,ce); //
-			return;
+			return null;
 		}
 		disposeExistingTabs();
 		fTabGroup = group;
@@ -926,18 +935,8 @@ private void showInstanceTabsFor(ILaunchConfigurationType configType) {
 				tab.setControl(control.getParent());
 			}
 		}
-		//set the default tab as the first one
-		if (tabs.length > 0) {
-			setActiveTab(tabs[0]);
-		}
-		// select same tab as before, if possible
-		for (ILaunchConfigurationTab t : tabs) {
-			if (t.getClass().equals(tabKind)) {
-				setActiveTab(t);
-				break;
-			}
-		}
 		fDescription = getDescription(configType);
+		return tabKind;
 	}
 
 	/**
@@ -1606,6 +1605,29 @@ protected void errorDialog(CoreException exception) {
 		ErrorDialog.openError(getShell(), null, null, exception.getStatus());
 	}
 
+	/**
+	 * @param tabKind The class of the tab that has to be activated.
+	 * @return <code>true</code> if a tab was activated, <code>false</code>
+	 *         otherwise.
+	 */
+	private boolean setActiveTab(Class<? extends ILaunchConfigurationTab> tabKind) {
+		if (tabKind == null) {
+			return false;
+		}
+
+		ILaunchConfigurationTab[] tabs = getTabs();
+
+		// select same tab as before, if possible
+		for (ILaunchConfigurationTab t : tabs) {
+			if (t.getClass().equals(tabKind)) {
+				setActiveTab(t);
+				return true;
+			}
+		}
+
+		return false;
+	}
+
 	/**
 	 * Sets the displayed tab to the given tab. Has no effect if the specified
 	 * tab is not one of the tabs being displayed in the dialog currently.