Fix window enter/leave events generation for wxChoice in wxGTK3

We need to connect these events to the internal GtkToggleButton taking
up the widget area and not the parent widget itself, which never gets
these events.

Closes #24295.

src/gtk/choice.cpp

@@ -17,6 +17,7 @@
 #endif
 
 #include "wx/gtk/private.h"
+#include "wx/gtk/private/event.h"
 #include "wx/gtk/private/eventsdisabler.h"
 #include "wx/gtk/private/list.h"
 #include "wx/gtk/private/value.h"
@@ -33,6 +34,26 @@ gtk_choice_changed_callback( GtkWidget *WXUNUSED(widget), wxChoice *choice )
     choice->SendSelectionChangedEvent(wxEVT_CHOICE);
 }
 
+#ifdef __WXGTK3__
+
+static gboolean
+wx_gtk_choice_enter_notify(GtkWidget* widget,
+                           GdkEventCrossing* gdk_event,
+                           wxChoice *choice)
+{
+    return wxGTKImpl::WindowEnterCallback(widget, gdk_event, choice);
+}
+
+static gboolean
+wx_gtk_choice_leave_notify(GtkWidget* widget,
+                           GdkEventCrossing* gdk_event,
+                           wxChoice* choice)
+{
+    return wxGTKImpl::WindowLeaveCallback(widget, gdk_event, choice);
+}
+
+#endif // __WXGTK3__
+
 }
 
 //-----------------------------------------------------------------------------
@@ -104,6 +125,35 @@ bool wxChoice::Create( wxWindow *parent, wxWindowID id,
     g_signal_connect_after (m_widget, "changed",
                             G_CALLBACK (gtk_choice_changed_callback), this);
 
+#ifdef __WXGTK3__
+    // Internal structure of GtkComboBoxText is complicated: it contains a
+    // GtkBox which contains a GtkToggleButton which contains another GtkBox
+    // which, in turn, contains GtkCellView (and more).
+    //
+    // And it's this internal GtkToggleButton which receives the mouse events
+    // and not the main widget itself, so find it and connect to its events.
+
+    // We could find it either by using gtk_container_forall() to get the box
+    // inside GtkComboBoxText and then get its only child, or by doing what we
+    // do here and getting GtkCellView directly and then getting its parent,
+    // which is simpler because GtkComboBoxText sets things up in such a way
+    // that its only child is the GtkCellView (even if, again, this is not how
+    // things really are internally).
+    auto cellView = gtk_bin_get_child(GTK_BIN(m_widget));
+    wxCHECK_MSG( cellView, true, "No cell view in GtkComboBoxText?" );
+
+    auto box = gtk_widget_get_parent(cellView);
+
+    auto button = gtk_widget_get_parent(box);
+    wxCHECK_MSG( GTK_IS_TOGGLE_BUTTON(button), true,
+                 "Unexpected grandparent of GtkCellView in GtkComboBoxText" );
+
+    g_signal_connect(button, "enter_notify_event",
+                     G_CALLBACK(wx_gtk_choice_enter_notify), this);
+    g_signal_connect(button, "leave_notify_event",
+                     G_CALLBACK(wx_gtk_choice_leave_notify), this);
+#endif // __WXGTK3__
+
     return true;
 }