If you make a typo like a missing quote: DEBUG_OPTIMIZATION = "-Og ${DEBUG_LEVELFLAG} then bitbake-layers add-layer hangs, e.g.: https://autobuilder.yoctoproject.org/typhoon/#/builders/83/builds/7129 which ran for an hour running: bitbake-layers add-layer ${BUILDDIR}/../meta-selftest
I took the revision that failed and tried to reproduce this and was not able to. I can only assume it is python version dependent and fixed in newer python versions...