Example:

• Have a foo.cpp file that includes foo.h that includes bar.h
• Have foo.cpp #include "foo.moc"

Currently if bar.h is changed, automoc will not rerun moc on foo.cpp. This is because automoc doesn't transfer the dependencies of foo.cpp to foo.moc, nor does it run the preprocessor on foo.moc to figure out the dependencies.

We will need this when doing feature re-configuration (for example you build qtbase with opengl feature enabled, and then you reconfigure with opengl feature disabled).

Currently moc is not rerun, and you get build failures.

Upstream issue
https://gitlab.kitware.com/cmake/cmake/issues/19058
https://gitlab.kitware.com/cmake/cmake/issues/17750