Gui: implement a workaround for MSYS2 to access QUiLoader via its Python interface

src/Ext/freecad/CMakeLists.txt

@@ -3,16 +3,18 @@ EXECUTE_PROCESS(COMMAND ${PYTHON_EXECUTABLE} -c
 OUTPUT_VARIABLE python_libs OUTPUT_STRIP_TRAILING_WHITESPACE )
 SET(PYTHON_MAIN_DIR ${python_libs})
 
-set(NAMESPACE_INIT "${CMAKE_BINARY_DIR}/Ext/freecad/__init__.py")
+set(NAMESPACE_DIR "${CMAKE_BINARY_DIR}/Ext/freecad")
+set(NAMESPACE_INIT "${NAMESPACE_DIR}/__init__.py")
 if (WIN32)
-	get_filename_component(FREECAD_LIBRARY_INSTALL_DIR "${CMAKE_INSTALL_BINDIR}"
+    get_filename_component(FREECAD_LIBRARY_INSTALL_DIR "${CMAKE_INSTALL_BINDIR}"
                        REALPATH BASE_DIR "${CMAKE_INSTALL_PREFIX}")
-	set( ${CMAKE_INSTALL_BINDIR})
+    set( ${CMAKE_INSTALL_BINDIR})
 else()
-	set(FREECAD_LIBRARY_INSTALL_DIR ${CMAKE_INSTALL_LIBDIR})
+    set(FREECAD_LIBRARY_INSTALL_DIR ${CMAKE_INSTALL_LIBDIR})
 endif()
 
 configure_file(__init__.py.template ${NAMESPACE_INIT})
+configure_file(UiTools.py ${NAMESPACE_DIR}/UiTools.py)
 
 if (INSTALL_TO_SITEPACKAGES)
     SET(SITE_PACKAGE_DIR ${PYTHON_MAIN_DIR}/freecad)
@@ -23,6 +25,7 @@ endif()
 INSTALL(
     FILES
         ${NAMESPACE_INIT}
+        UiTools.py
     DESTINATION
         ${SITE_PACKAGE_DIR}
 )

src/Ext/freecad/UiTools.py

@@ -0,0 +1,21 @@
+# (c) 2021 Werner Mayer LGPL
+
+from PySide2 import QtUiTools
+from PySide2 import QtCore
+import FreeCADGui as Gui
+
+
+class QUiLoader(QtUiTools.QUiLoader):
+    """
+    This is an extension of Qt's QUiLoader to also create custom widgets
+    """
+    def __init__(self, arg = None):
+        super(QUiLoader, self).__init__(arg)
+        self.ui = Gui.PySideUic
+    
+    def createWidget(self, className, parent = None, name = ""):
+        widget = self.ui.createCustomWidget(className, parent, name)
+        if not widget:
+            widget = super(QUiLoader, self).createWidget(className, parent, name)
+        return widget
+