1. Create a new Qt Widgets Application using build system CMake.
2. Open the project's file mainwindow.ui in Design mode.
3. Drag a Push Button onto the Window preview.
4. Open the project's file mainwindow.cpp.
5. In the ctor of MainWindow, add the line:

   ui->
   

   and wait for the proposal popup.
   There will be no such popup.

When using qmake instead of CMake, the proposal popup will appear and show "pushButton".

Found and tested by Squish test tst_designer_autocomplete.