LibCore: Make CObject reference-counted

Okay, I've spent a whole day on this now, and it finally kinda works!
With this patch, CObject and all of its derived classes are reference
counted instead of tree-owned.

The previous, Qt-like model was nice and familiar, but ultimately also
outdated and difficult to reason about.

CObject-derived types should now be stored in RefPtr/NonnullRefPtr and
each class can be constructed using the forwarding construct() helper:

    auto widget = GWidget::construct(parent_widget);

Note that construct() simply forwards all arguments to an existing
constructor. It is inserted into each class by the C_OBJECT macro,
see CObject.h to understand how that works.

CObject::delete_later() disappears in this patch, as there is no longer
a single logical owner of a CObject.

6 files changed, 20 insertions, 21 deletions

diff --git a/Libraries/LibGUI/GAboutDialog.cpp b/Libraries/LibGUI/GAboutDialog.cpp
index 4fa3666d9e..5bc8c50ed6 100644
--- a/Libraries/LibGUI/GAboutDialog.cpp
+++ b/Libraries/LibGUI/GAboutDialog.cpp
@@ -18,7 +18,7 @@ GAboutDialog::GAboutDialog(const StringView& name, const GraphicsBitmap* icon, C
     widget->set_fill_with_background_color(true);
     widget->set_layout(make<GBoxLayout>(Orientation::Horizontal));
 
-    auto left_container = GWidget::construct(widget);
+    auto left_container = GWidget::construct(widget.ptr());
     left_container->set_size_policy(SizePolicy::Fixed, SizePolicy::Fill);
     left_container->set_preferred_size(48, 0);
     left_container->set_layout(make<GBoxLayout>(Orientation::Vertical));
@@ -28,7 +28,7 @@ GAboutDialog::GAboutDialog(const StringView& name, const GraphicsBitmap* icon, C
     icon_label->set_preferred_size(40, 40);
     left_container->layout()->add_spacer();
 
-    auto right_container = GWidget::construct(widget);
+    auto right_container = GWidget::construct(widget.ptr());
     right_container->set_layout(make<GBoxLayout>(Orientation::Vertical));
     right_container->layout()->set_margins({ 0, 4, 4, 4 });
 
@@ -46,7 +46,7 @@ GAboutDialog::GAboutDialog(const StringView& name, const GraphicsBitmap* icon, C
 
     right_container->layout()->add_spacer();
 
-    auto button_container = GWidget::construct(right_container);
+    auto button_container = GWidget::construct(right_container.ptr());
     button_container->set_size_policy(SizePolicy::Fill, SizePolicy::Fixed);
     button_container->set_preferred_size(0, 20);
     button_container->set_layout(make<GBoxLayout>(Orientation::Horizontal));
diff --git a/Libraries/LibGUI/GApplication.cpp b/Libraries/LibGUI/GApplication.cpp
index a2172fe552..1c404225c9 100644
--- a/Libraries/LibGUI/GApplication.cpp
+++ b/Libraries/LibGUI/GApplication.cpp
@@ -110,7 +110,6 @@ void GApplication::hide_tooltip()
 {
     if (m_tooltip_window) {
         m_tooltip_window->hide();
-        delete m_tooltip_window;
         m_tooltip_window = nullptr;
     }
 }
diff --git a/Libraries/LibGUI/GFilePicker.cpp b/Libraries/LibGUI/GFilePicker.cpp
index ab60cb58a4..efe1f6444a 100644
--- a/Libraries/LibGUI/GFilePicker.cpp
+++ b/Libraries/LibGUI/GFilePicker.cpp
@@ -57,11 +57,11 @@ GFilePicker::GFilePicker(Mode mode, const StringView& file_name, const StringVie
     horizontal_container->set_fill_with_background_color(true);
     horizontal_container->set_background_color(Color::WarmGray);
 
-    auto vertical_container = GWidget::construct(horizontal_container);
+    auto vertical_container = GWidget::construct(horizontal_container.ptr());
     vertical_container->set_layout(make<GBoxLayout>(Orientation::Vertical));
     vertical_container->layout()->set_spacing(4);
 
-    auto upper_container = GWidget::construct(vertical_container);
+    auto upper_container = GWidget::construct(vertical_container.ptr());
     upper_container->set_layout(make<GBoxLayout>(Orientation::Horizontal));
     upper_container->layout()->set_spacing(4);
     upper_container->set_size_policy(SizePolicy::Fill, SizePolicy::Fixed);
@@ -118,13 +118,13 @@ GFilePicker::GFilePicker(Mode mode, const StringView& file_name, const StringVie
     });
     toolbar->add_action(*mkdir_action);
 
-    auto lower_container = GWidget::construct(vertical_container);
+    auto lower_container = GWidget::construct(vertical_container.ptr());
     lower_container->set_layout(make<GBoxLayout>(Orientation::Vertical));
     lower_container->layout()->set_spacing(4);
     lower_container->set_size_policy(SizePolicy::Fill, SizePolicy::Fixed);
     lower_container->set_preferred_size(0, 60);
 
-    auto filename_container = GWidget::construct(lower_container);
+    auto filename_container = GWidget::construct(lower_container.ptr());
     filename_container->set_size_policy(SizePolicy::Fill, SizePolicy::Fixed);
     filename_container->set_preferred_size(0, 20);
     filename_container->set_layout(make<GBoxLayout>(Orientation::Horizontal));
@@ -132,7 +132,7 @@ GFilePicker::GFilePicker(Mode mode, const StringView& file_name, const StringVie
     filename_label->set_text_alignment(TextAlignment::CenterLeft);
     filename_label->set_size_policy(SizePolicy::Fixed, SizePolicy::Fill);
     filename_label->set_preferred_size(60, 0);
-    m_filename_textbox = GTextBox::construct(filename_container);
+    m_filename_textbox = GTextBox::construct(filename_container.ptr());
     if (m_mode == Mode::Save) {
         m_filename_textbox->set_text(file_name);
         m_filename_textbox->set_focus(true);
@@ -155,7 +155,7 @@ GFilePicker::GFilePicker(Mode mode, const StringView& file_name, const StringVie
         set_preview(path);
     };
 
-    auto button_container = GWidget::construct(lower_container);
+    auto button_container = GWidget::construct(lower_container.ptr());
     button_container->set_size_policy(SizePolicy::Fill, SizePolicy::Fixed);
     button_container->set_preferred_size(0, 20);
     button_container->set_layout(make<GBoxLayout>(Orientation::Horizontal));
diff --git a/Libraries/LibGUI/GInputBox.cpp b/Libraries/LibGUI/GInputBox.cpp
index 483cb12045..521e2c0911 100644
--- a/Libraries/LibGUI/GInputBox.cpp
+++ b/Libraries/LibGUI/GInputBox.cpp
@@ -42,12 +42,12 @@ void GInputBox::build()
     m_text_editor->set_size_policy(SizePolicy::Fill, SizePolicy::Fixed);
     m_text_editor->set_preferred_size(0, 19);
 
-    auto button_container_outer = GWidget::construct(widget);
+    auto button_container_outer = GWidget::construct(widget.ptr());
     button_container_outer->set_size_policy(SizePolicy::Fill, SizePolicy::Fixed);
     button_container_outer->set_preferred_size(0, 20);
     button_container_outer->set_layout(make<GBoxLayout>(Orientation::Vertical));
 
-    auto button_container_inner = GWidget::construct(button_container_outer);
+    auto button_container_inner = GWidget::construct(button_container_outer.ptr());
     button_container_inner->set_layout(make<GBoxLayout>(Orientation::Horizontal));
     button_container_inner->layout()->set_spacing(8);
 
diff --git a/Libraries/LibGUI/GMessageBox.cpp b/Libraries/LibGUI/GMessageBox.cpp
index c074d65210..d59c03bd25 100644
--- a/Libraries/LibGUI/GMessageBox.cpp
+++ b/Libraries/LibGUI/GMessageBox.cpp
@@ -64,7 +64,7 @@ void GMessageBox::build()
 
     ObjectPtr<GWidget> message_container = widget;
     if (m_type != Type::None) {
-        message_container = GWidget::construct(widget);
+        message_container = GWidget::construct(widget.ptr());
         message_container->set_layout(make<GBoxLayout>(Orientation::Horizontal));
         message_container->layout()->set_margins({ 8, 0, 8, 0 });
         message_container->layout()->set_spacing(8);
@@ -80,7 +80,7 @@ void GMessageBox::build()
     label->set_size_policy(SizePolicy::Fill, SizePolicy::Fixed);
     label->set_preferred_size(text_width, 16);
 
-    auto button_container = GWidget::construct(widget);
+    auto button_container = GWidget::construct(widget.ptr());
     button_container->set_layout(make<GBoxLayout>(Orientation::Horizontal));
     button_container->layout()->set_spacing(5);
     button_container->layout()->set_margins({ 15, 0, 15, 0 });
diff --git a/Libraries/LibGUI/GWidget.cpp b/Libraries/LibGUI/GWidget.cpp
index 66ff1eed53..1aa678c846 100644
--- a/Libraries/LibGUI/GWidget.cpp
+++ b/Libraries/LibGUI/GWidget.cpp
@@ -325,13 +325,13 @@ Rect GWidget::screen_relative_rect() const
 GWidget* GWidget::child_at(const Point& point) const
 {
     for (int i = children().size() - 1; i >= 0; --i) {
-        if (!is<GWidget>(*children()[i]))
+        if (!is<GWidget>(children()[i]))
             continue;
-        auto& child = to<GWidget>(*children()[i]);
+        auto& child = to<GWidget>(children()[i]);
         if (!child.is_visible())
             continue;
         if (child.relative_rect().contains(point))
-            return &child;
+            return const_cast<GWidget*>(&child);
     }
     return nullptr;
 }
@@ -492,7 +492,7 @@ void GWidget::move_to_front()
     parent->children().remove_first_matching([this](auto& entry) {
         return entry == this;
     });
-    parent->children().append(this);
+    parent->children().append(*this);
     parent->update();
 }
 
@@ -506,7 +506,7 @@ void GWidget::move_to_back()
     parent->children().remove_first_matching([this](auto& entry) {
         return entry == this;
     });
-    parent->children().prepend(this);
+    parent->children().prepend(*this);
     parent->update();
 }
 
@@ -515,7 +515,7 @@ bool GWidget::is_frontmost() const
     auto* parent = parent_widget();
     if (!parent)
         return true;
-    return parent->children().last() == this;
+    return &parent->children().last() == this;
 }
 
 bool GWidget::is_backmost() const
@@ -523,7 +523,7 @@ bool GWidget::is_backmost() const
     auto* parent = parent_widget();
     if (!parent)
         return true;
-    return parent->children().first() == this;
+    return &parent->children().first() == this;
 }
 
 GAction* GWidget::action_for_key_event(const GKeyEvent& event)