Hmm, really weird. It was a complete fresh checkout. Created a new directory, new src, imported the repositories and ran ament. When I do the same thing with beta1 (different workspace, but clean checkout as well), everything compiles fine. However master fails with the error above.
I’m using cmake version 3.5.1
python: Python 2.7.12
python3: Python 3.5.2
vcs status --hide shows nothing …