Combining Windows and Linux results?

I’m using codecov to report on coverage.py itself: https://codecov.io/gh/nedbat/coveragepy

But all of my “if WINDOWS:” code is shown as uncovered, even though my AppVeyor builds succeed and are shown on the builds page: https://codecov.io/gh/nedbat/coveragepy/commit/822953106a01aaf1f88bc5e5a63fe693d42c0c00/builds

Do I need to create a codecov.yml file with “fixes” for Windows paths? Searching around other projects, I don’t see people doing that. The codecov docs mention “built in” rules for mapping disparate paths together, but I couldn’t find details of those.

What do people do to make this work?

Thanks.