KDE runs a tool that checks cdoe for common potential errors or provides recommendations on make code cleaner.

You can find the issues for KDE's PIM libraries here: EBN Krazy Issues for KDE PIM libraries

Note: some valid issues can not be fixed at the time because of API stability guarantees. One example is adding the "explicit" keyword to constructors of classes in public API, i.e. headers that get installed (See "install" sections in the respective CMakeLists.txt files)

The task is to fix 31 of any of those and submit them as a review request for group "kdepimlibs" on KDE Review Board

Go here for additional pointers