LibGUI: Add Widget::has_focus_within()

This returns true if the widget has focus, or if one of its descendant
widgets does. Use this in StackWidget and TabWidget.

This also fixes HackStudio crashing on startup in StackWidget, due to
running before the window has a focused widget.

4 files changed, 18 insertions, 2 deletions

diff --git a/Libraries/LibGUI/StackWidget.cpp b/Libraries/LibGUI/StackWidget.cpp
index 8af53e00a9..531346195e 100644
--- a/Libraries/LibGUI/StackWidget.cpp
+++ b/Libraries/LibGUI/StackWidget.cpp
@@ -43,7 +43,7 @@ void StackWidget::set_active_widget(Widget* widget)
     if (widget == m_active_widget)
         return;
 
-    bool active_widget_had_focus = m_active_widget && window() && (window()->focused_widget() == m_active_widget || m_active_widget->is_ancestor_of(*window()->focused_widget()));
+    bool active_widget_had_focus = m_active_widget && m_active_widget->has_focus_within();
 
     if (m_active_widget)
         m_active_widget->set_visible(false);
diff --git a/Libraries/LibGUI/TabWidget.cpp b/Libraries/LibGUI/TabWidget.cpp
index 69d8914f97..4bafddd049 100644
--- a/Libraries/LibGUI/TabWidget.cpp
+++ b/Libraries/LibGUI/TabWidget.cpp
@@ -88,12 +88,13 @@ void TabWidget::update_focus_policy()
         policy = FocusPolicy::NoFocus;
     set_focus_policy(policy);
 }
+
 void TabWidget::set_active_widget(Widget* widget)
 {
     if (widget == m_active_widget)
         return;
 
-    bool active_widget_had_focus = m_active_widget && window() && (window()->focused_widget() == m_active_widget || m_active_widget->is_ancestor_of(*window()->focused_widget()));
+    bool active_widget_had_focus = m_active_widget && m_active_widget->has_focus_within();
 
     if (m_active_widget)
         m_active_widget->set_visible(false);
diff --git a/Libraries/LibGUI/Widget.cpp b/Libraries/LibGUI/Widget.cpp
index b3997db3c3..69327e5c50 100644
--- a/Libraries/LibGUI/Widget.cpp
+++ b/Libraries/LibGUI/Widget.cpp
@@ -989,4 +989,16 @@ Widget* Widget::find_descendant_by_name(const String& name)
     });
     return found_widget;
 }
+
+bool Widget::has_focus_within() const
+{
+    auto* window = this->window();
+    if (!window)
+        return false;
+    if (!window->focused_widget())
+        return false;
+    auto& effective_focus_widget = focus_proxy() ? *focus_proxy() : *this;
+    return window->focused_widget() == &effective_focus_widget || is_ancestor_of(*window->focused_widget());
+}
+
 }
diff --git a/Libraries/LibGUI/Widget.h b/Libraries/LibGUI/Widget.h
index e494f6f81f..10d3366cfc 100644
--- a/Libraries/LibGUI/Widget.h
+++ b/Libraries/LibGUI/Widget.h
@@ -165,6 +165,9 @@ public:
     bool is_focused() const;
     void set_focus(bool, FocusSource = FocusSource::Programmatic);
 
+    // Returns true if this widget or one of its descendants is focused.
+    bool has_focus_within() const;
+
     Widget* focus_proxy() { return m_focus_proxy; }
     const Widget* focus_proxy() const { return m_focus_proxy; }
     void set_focus_proxy(Widget*);