Suppress focus loss on opening combobox popup in wxGTK

Make GTKHandleFocusOut() virtual and override it in wxChoice in order to
avoid generating wxEVT_KILL_FOCUS events when the combobox dropdown
button is clicked.

This is important because it allows fatal problems when using a
combobox-based in-place editor in wxDataViewCtrl as getting these events
totally broke the UI before.

See #17034.

docs/changes.txt

@@ -206,6 +206,7 @@ wxGTK:
 - Implement XYToPosition() for single-line wxTextCtrl.
 - Implement ShowPosition() for single-line wxTextCtrl.
 - Improve wx{Client,Paint,Screen,Window}DC::GetPPI() (GTK+ 3).
+- Suppress focus loss events for wxChoice and wxComboBox on opening popup.
 
 wxMSW:
 

include/wx/gtk/choice.h

@@ -101,6 +101,7 @@ protected:
     virtual void DoClear() wxOVERRIDE;
     virtual void DoDeleteOneItem(unsigned int n) wxOVERRIDE;
 
+    virtual bool GTKHandleFocusOut() wxOVERRIDE;
     virtual GdkWindow *GTKGetWindow(wxArrayGdkWindows& windows) const wxOVERRIDE;
     virtual void DoApplyWidgetStyle(GtkRcStyle *style) wxOVERRIDE;
 

include/wx/gtk/window.h

@@ -197,7 +197,7 @@ public:
     GdkWindow* GTKGetDrawingWindow() const;
 
     bool GTKHandleFocusIn();
-    bool GTKHandleFocusOut();
+    virtual bool GTKHandleFocusOut();
     void GTKHandleFocusOutNoDeferring();
     void GTKHandleDeferredFocusOut();
 

src/gtk/choice.cpp

@@ -111,6 +111,23 @@ wxChoice::~wxChoice()
  #endif // __WXGTK3__
 }
 
+bool wxChoice::GTKHandleFocusOut()
+{
+    if ( wx_is_at_least_gtk2(10) )
+    {
+        gboolean isShown;
+        g_object_get( m_widget, "popup-shown", &isShown, NULL );
+
+        // Don't send "focus lost" events if the focus is grabbed by our own
+        // popup, it counts as part of this window, even though wx doesn't know
+        // about it (and can't, because GtkComboBox doesn't expose it).
+        if ( isShown )
+            return true;
+    }
+
+    return wxChoiceBase::GTKHandleFocusOut();
+}
+
 void wxChoice::GTKInsertComboBoxTextItem( unsigned int n, const wxString& text )
 {
 #ifdef __WXGTK3__