These issues mentions that it works but it still does not in 4.15 for me:

https://bugreports.qt.io/browse/QTCREATORBUG-21060

https://bugreports.qt.io/browse/QTCREATORBUG-21452

• The analysis panel does not show header files.
• They aren't analyzed on the fly when opening / editing a header file either.

I attached a repro.
To see it in action :

• Enable clang-tidy config-file based checks in Qt Creator
• main.cpp : there is a warning

• main.hpp : there isn't

Both files are added as source files to CMake and are seen as project files.