UI/Qt: Make TabWidget responsible for new-tab button positioning

Makes use of the fact that QTabWidget automatically reserves space
for "corner widgets", and gives us the ability to override their
location with a custom style.

Also, determine the height of the new-tab button using the height of the
tab bar, instead of a hard-coded 32px which was too tall on MacOS.

Ladybird/Qt/BrowserWindow.cpp

@@ -3,6 +3,7 @@
  * Copyright (c) 2022, Matthew Costa <ucosty@gmail.com>
  * Copyright (c) 2022, Filiph Sandström <filiph.sandstrom@filfatstudios.com>
  * Copyright (c) 2023, Linus Groh <linusg@serenityos.org>
+ * Copyright (c) 2024, Sam Atkins <sam@ladybird.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -679,6 +680,7 @@ BrowserWindow::BrowserWindow(Vector<URL::URL> const& initial_urls, WebView::Cook
     m_new_tab_button_toolbar->setMovable(false);
     m_new_tab_button_toolbar->setStyleSheet("QToolBar { background: transparent; }");
     m_new_tab_button_toolbar->setIconSize(QSize(16, 16));
+    m_tabs_container->setCornerWidget(m_new_tab_button_toolbar, Qt::TopRightCorner);
 
     setCentralWidget(m_tabs_container);
     setContextMenuPolicy(Qt::PreventContextMenu);
@@ -693,20 +695,6 @@ void BrowserWindow::set_current_tab(Tab* tab)
     }
 }
 
-void BrowserWindow::update_new_tab_button()
-{
-    if (m_new_tab_button_toolbar == nullptr || m_tabs_container == nullptr || m_tabs_container->count() < 1)
-        return;
-    QSize tab_bar_size = m_tabs_container->tabBar()->sizeHint();
-    int window_width = this->rect().width();
-    QRect new_rect;
-    new_rect.setX(qMin(tab_bar_size.width(), window_width - 32));
-    new_rect.setWidth(32);
-    new_rect.setHeight(32);
-    m_tabs_container->tabBar()->setMaximumWidth(window_width - 32);
-    m_new_tab_button_toolbar->setGeometry(new_rect);
-}
-
 void BrowserWindow::debug_request(ByteString const& request, ByteString const& argument)
 {
     if (!m_current_tab)
@@ -854,8 +842,6 @@ void BrowserWindow::initialize_tab(Tab* tab)
     tab->set_navigator_compatibility_mode(navigator_compatibility_mode());
     tab->set_enable_do_not_track(Settings::the()->enable_do_not_track());
     tab->view().set_preferred_color_scheme(m_preferred_color_scheme);
-
-    update_new_tab_button();
 }
 
 void BrowserWindow::activate_tab(int index)
@@ -869,8 +855,6 @@ void BrowserWindow::close_tab(int index)
     m_tabs_container->removeTab(index);
     tab->deleteLater();
 
-    update_new_tab_button();
-
     if (m_tabs_container->count() == 0)
         close();
 }
@@ -1197,7 +1181,6 @@ void BrowserWindow::resizeEvent(QResizeEvent* event)
     for_each_tab([&](auto& tab) {
         tab.view().set_window_size({ frameSize().width() * m_device_pixel_ratio, frameSize().height() * m_device_pixel_ratio });
     });
-    update_new_tab_button();
 }
 
 void BrowserWindow::moveEvent(QMoveEvent* event)

Ladybird/Qt/BrowserWindow.h

@@ -184,8 +184,6 @@ private:
     Web::CSS::PreferredColorScheme m_preferred_color_scheme;
     void set_preferred_color_scheme(Web::CSS::PreferredColorScheme color_scheme);
 
-    void update_new_tab_button();
-
     QTabWidget* m_tabs_container { nullptr };
     Tab* m_current_tab { nullptr };
     QMenu* m_zoom_menu { nullptr };

Ladybird/Qt/TabBar.cpp

@@ -1,6 +1,7 @@
 /*
  * Copyright (c) 2024, Tim Flynn <trflynn89@serenityos.org>
  * Copyright (c) 2024, Jamie Mansfield <jmansfield@cadixdev.org>
+ * Copyright (c) 2024, Sam Atkins <sam@ladybird.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -12,6 +13,7 @@
 #include <QContextMenuEvent>
 #include <QEvent>
 #include <QPushButton>
+#include <QStylePainter>
 
 namespace Ladybird {
 
@@ -50,6 +52,8 @@ TabWidget::TabWidget(QWidget* parent)
     setMovable(true);
     setTabsClosable(true);
 
+    setStyle(new TabStyle(this));
+
     installEventFilter(parent);
 }
 
@@ -70,4 +74,27 @@ bool TabBarButton::event(QEvent* event)
     return QPushButton::event(event);
 }
 
+TabStyle::TabStyle(QObject* parent)
+{
+    setParent(parent);
+}
+
+QRect TabStyle::subElementRect(QStyle::SubElement sub_element, QStyleOption const* option, QWidget const* widget) const
+{
+    // Place our add-tab button (set as the top-right corner widget) directly after the last tab
+    if (sub_element == QStyle::SE_TabWidgetRightCorner) {
+        auto* tab_widget = verify_cast<TabWidget>(widget);
+        auto tab_bar_size = tab_widget->tabBar()->sizeHint();
+        auto new_tab_button_size = tab_bar_size.height();
+        return QRect {
+            qMin(tab_bar_size.width(), tab_widget->width() - new_tab_button_size),
+            0,
+            new_tab_button_size,
+            new_tab_button_size
+        };
+    }
+
+    return QProxyStyle::subElementRect(sub_element, option, widget);
+}
+
 }

Ladybird/Qt/TabBar.h

@@ -1,12 +1,14 @@
 /*
  * Copyright (c) 2024, Tim Flynn <trflynn89@serenityos.org>
  * Copyright (c) 2024, Jamie Mansfield <jmansfield@cadixdev.org>
+ * Copyright (c) 2024, Sam Atkins <sam@ladybird.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
 #pragma once
 
+#include <QProxyStyle>
 #include <QPushButton>
 #include <QTabBar>
 #include <QTabWidget>
@@ -45,4 +47,13 @@ protected:
     virtual bool event(QEvent* event) override;
 };
 
+class TabStyle : public QProxyStyle {
+    Q_OBJECT
+
+public:
+    explicit TabStyle(QObject* parent = nullptr);
+
+    virtual QRect subElementRect(QStyle::SubElement, QStyleOption const*, QWidget const*) const override;
+};
+
 }