undo.pro Example File
tools/undo/undo.pro
  QT += widgets
  requires(qtConfig(undoview))
  SOURCES += main.cpp mainwindow.cpp commands.cpp document.cpp
  HEADERS += mainwindow.h commands.h document.h
  FORMS += mainwindow.ui
  build_all:!build_pass {
      CONFIG -= build_all
      CONFIG += release
  }
  RESOURCES += undo.qrc
  # install
  target.path = $$[QT_INSTALL_EXAMPLES]/widgets/tools/undo
  INSTALLS += target