ProjectExplorer: Fix some problems with plugin unloading

It was not possible to return false from
ProjectExplorerPlugin::initialize() without triggering crashes.

Change-Id: I96b2f80c835e69769f64f9b9c61f473e9ff88623
Reviewed-by: hjk <hjk@qt.io>

src/plugins/coreplugin/fancyactionbar.cpp

@@ -176,7 +176,7 @@ void FancyToolButton::paintEvent(QPaintEvent *event)
                                      : QIcon::Disabled;
     QRect iconRect(0, 0, Constants::MODEBAR_ICON_SIZE, Constants::MODEBAR_ICON_SIZE);
 
-    const bool isTitledAction = defaultAction()->property("titledAction").toBool();
+    const bool isTitledAction = defaultAction() && defaultAction()->property("titledAction").toBool();
     // draw popup texts
     if (isTitledAction && !m_iconsOnly) {
         QFont normalFont(painter.font());
@@ -286,7 +286,7 @@ QSize FancyToolButton::sizeHint() const
     }
 
     QSizeF buttonSize = iconSize().expandedTo(QSize(64, 38));
-    if (defaultAction()->property("titledAction").toBool()) {
+    if (defaultAction() && defaultAction()->property("titledAction").toBool()) {
         QFont boldFont(font());
         boldFont.setPointSizeF(StyleHelper::sidebarFontSize());
         boldFont.setBold(true);

src/plugins/coreplugin/modemanager.cpp

@@ -238,6 +238,9 @@ void ModeManager::removeMode(IMode *mode)
 {
     const int index = d->m_modes.indexOf(mode);
     d->m_modes.remove(index);
+    if (d->m_startingUp)
+        return;
+
     d->m_modeCommands.remove(index);
     d->m_modeStack->removeTab(index);
 

src/plugins/coreplugin/outputpanemanager.cpp

@@ -115,6 +115,7 @@ IOutputPane::~IOutputPane()
     const int i = Utils::indexOf(g_outputPanes, Utils::equal(&OutputPaneData::pane, this));
     QTC_ASSERT(i >= 0, return);
     delete g_outputPanes.at(i).button;
+    g_outputPanes.removeAt(i);
 
     delete m_zoomInButton;
     delete m_zoomOutButton;

src/plugins/projectexplorer/projectexplorer.cpp

@@ -2772,6 +2772,8 @@ QPair<bool, QString> ProjectExplorerPluginPrivate::buildSettingsEnabledForSessio
 
 bool ProjectExplorerPlugin::coreAboutToClose()
 {
+    if (!m_instance)
+        return true;
     if (BuildManager::isBuilding()) {
         QMessageBox box;
         QPushButton *closeAnyway = box.addButton(tr("Cancel Build && Close"), QMessageBox::AcceptRole);

src/plugins/projectexplorer/session.cpp

@@ -156,6 +156,8 @@ SessionManager::SessionManager(QObject *parent) : QObject(parent)
 
 SessionManager::~SessionManager()
 {
+    EditorManager::setWindowTitleAdditionHandler({});
+    EditorManager::setSessionTitleHandler({});
     emit m_instance->aboutToUnloadSession(d->m_sessionName);
     delete d->m_writer;
     delete d;

src/plugins/welcome/welcomeplugin.cpp

@@ -429,6 +429,13 @@ void WelcomeMode::addPage(IWelcomePage *page)
     stackPage->setAutoFillBackground(true);
     m_pageStack->insertWidget(idx, stackPage);
 
+    connect(page, &QObject::destroyed, this, [this, page, stackPage, pageButton] {
+        m_pluginList.removeOne(page);
+        m_pageButtons.removeOne(pageButton);
+        delete pageButton;
+        delete stackPage;
+    });
+
     auto onClicked = [this, pageId, stackPage] {
         m_activePage = pageId;
         m_pageStack->setCurrentWidget(stackPage);