If I understand correctly and, let's suppose, libQtFoo 5.10.2 is built with a patched compat 12, then all applications rebuilt against 5.10.2 would require at very least 5.10.2 even if symbols files allowed it to depend on a minor version.
If this is true is more or less what we are currently forcing with any package that B-Ds on qtbase5-dev, although this would also mean that packages that just B-D on qtbase5-private-dev will get the same behavior (even if they do not list qtbase5-dev as a B-D and not taking into account the qtbase-abi-x-y-z dependency). The only thing I don't know from this is iif symbols files dependency info is totally discarded or the dependency on qtbase-abi-x-y-z would still be get trough them for packages using private API. Niels: like in [1] we use dpkg-symbols' "alternative-dependency.template" to track packages using private API. As long as this is kept then the change, I think, should be ok. [1] <https://salsa.debian.org/qt-kde-team/qt/qtbase/blob/master/debian/libqt5core5a.symbols> -- Lisandro Damián Nicanor Pérez Meyer http://perezmeyer.com.ar/ http://perezmeyer.blogspot.com/
