I have checked d73e736 on one of my projects:

• Works well with Python 3.7
• Works well with Python 3.6 + pip install dataclasses

FYI, the mkdocs* versions:

mkdocs                       1.1.2      
mkdocs-codeinclude-plugin    0.1.0-local
mkdocs-macros-plugin         0.4.20     
mkdocs-macros-test           0.1.0      
mkdocs-material              6.1.2      
mkdocs-material-extensions   1.0.1      

Thanks for update - I was almost writing a custom plugin, when I find yours, then almost starting to impl. this, when I saw the PR.

Thanks @LajosCseppento - I've tested it myself and been happy with it, and it's great to have your additional input.

I'll merge and release.