Warn projects not to use it because PUBLIC_LIBRARIES don't make sense for executable targets and it also led to some issues in the internal functions where some of them did not expect to receive PUBLIC_LIBRARIES. To ensure builds don't needlessly break, treat PUBLIC_LIBRARIES values as regular LIBRARIES. In the future we might add an error instead. Using PUBLIC_LIBRARIES in qt_internal_add_app, etc, accidentally worked because the option name and the values following it were parsed as values of the "previous" option, like SOURCES or INCLUDE_DIRECTORIES or LIBRARIES, and when those got passed through to qt_internal_extend_target, things magically worked. We have a lot of projects using PUBLIC_LIBRARIES, mostly due to the way qmake pro files were written and how pro2cmake converted them. We'll have to clean up each repo. Change-Id: I69e09d34afdf98f0d47c08d324643fc986f8131c Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>