Core: Add a way to delay-construct mode widgets

... and use it for edit mode.

There's currently no real effect as the mode bar population in
ModeManagerPrivate::extensionsInitializedHelper() accesses all
IMode::widget() and triggers the creation, but in principle we
could pass the functor instead of the widget down to and store in
FancyTabWidget and only use it when a mode gets activated.

Change-Id: I4c4a276bc025abce1ff47c68b060c67b5c8e5170
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/coreplugin/editmode.cpp

@@ -74,14 +74,11 @@ EditMode::EditMode()
     connect(ModeManager::instance(), &ModeManager::currentModeChanged,
             this, &EditMode::grabEditorManager);
 
-    setWidget(new EditModeWidget);
+    setWidgetCreator([] { return new EditModeWidget; });
     setContext(Context(Constants::C_EDIT_MODE, Constants::C_NAVIGATION_PANE));
 }
 
-EditMode::~EditMode()
-{
-    delete widget();
-}
+EditMode::~EditMode() = default;
 
 void EditMode::grabEditorManager(Utils::Id mode)
 {

src/plugins/coreplugin/imode.cpp

@@ -7,6 +7,7 @@
 
 #include <utils/aspects.h>
 #include <utils/fancymainwindow.h>
+#include <utils/qtcassert.h>
 
 #include <aggregation/aggregate.h>
 
@@ -27,6 +28,7 @@ public:
     Utils::Id m_id;
     Context m_context;
     QPointer<QWidget> m_widget;
+    std::function<QWidget *()> m_widgetCreator;
     bool m_isEnabled = true;
     BoolAspect m_isVisible;
 };
@@ -127,7 +129,11 @@ IMode::IMode(QObject *parent)
     ModeManager::addMode(this);
 }
 
-IMode::~IMode() = default;
+IMode::~IMode()
+{
+    if (m_d->m_widgetCreator)
+        delete m_d->m_widget;
+}
 
 QString IMode::displayName() const
 {
@@ -203,9 +209,18 @@ void IMode::setContext(const Context &context)
 
 void IMode::setWidget(QWidget *widget)
 {
+    QTC_ASSERT(!m_d->m_widgetCreator,
+               qWarning("A mode widget should not be set if there is already a widget creator"));
     m_d->m_widget = widget;
 }
 
+void IMode::setWidgetCreator(const std::function<QWidget *()> &widgetCreator)
+{
+    QTC_ASSERT(!m_d->m_widget,
+               qWarning("A mode widget widgetCreator should not be set if there is already a widget"));
+    m_d->m_widgetCreator = widgetCreator;
+}
+
 Utils::FancyMainWindow *IMode::mainWindow()
 {
     if (m_d->m_mainWindow)
@@ -257,6 +272,8 @@ Context IMode::context() const
 
 QWidget *IMode::widget() const
 {
+    if (!m_d->m_widget && m_d->m_widgetCreator)
+        m_d->m_widget = m_d->m_widgetCreator();
     return m_d->m_widget;
 }
 

src/plugins/coreplugin/imode.h

@@ -56,6 +56,7 @@ public:
     void setMenu(std::function<void(QMenu *)> menuFunction);
     void setContext(const Context &context);
     void setWidget(QWidget *widget);
+    void setWidgetCreator(const std::function<QWidget *()> &widgetCreator);
 
     Utils::FancyMainWindow *mainWindow();
     void setMainWindow(Utils::FancyMainWindow *mw);

src/plugins/debugger/debuggerplugin.cpp

@@ -500,13 +500,11 @@ public:
         setPriority(85);
         setId(MODE_DEBUG);
 
-        setWidget(new DebugModeWidget);
+        setWidgetCreator([] { return new DebugModeWidget; });
         setMainWindow(DebuggerMainWindow::instance());
 
         setMenu(&DebuggerMainWindow::addPerspectiveMenu);
     }
-
-    ~DebugMode() { delete widget(); }
 };
 
 ///////////////////////////////////////////////////////////////////////