Trying to use latest mbed feature branch does not work

I am trying to use the latest mbed feature branch for Nordic targets.
I cloned ot into the packages folder and moved the .json and platformIO folder from the old one to the freshly cloned one.
but somehow I keep getting the error:

ImportError: cannot import name merge_region_list:

even if I reert my changes, this error will persist. I have to reinstall platformIO to get rid of it.
what am I doing wrong?


We support only stable version of mbed OS.

so there is no possibility to use a feature branch with PIO? not even unsupported ways?

You can try to go into your <home dir>/.platformio/platforms/nordicnrf52/platform.json and do the same change as in Update mbed framework to 5.12.2 · platformio/platform-ststm32@80701df · GitHub to get mbed-os 5.12.2. No idea if it will actually result in a functioning binary.

We added support for mbed OS 5.12.2 yesterday. Please switch to upstream version Nordic nRF52 — PlatformIO latest documentation