controller-gen treats the file as a package, which causes error. This command works in v0.7.0. I think it's due to #663
Specifically this part
https://github.com/kubernetes-sigs/controller-tools/pull/663/files#diff-19effe657639f31c4b607076be411e82add5f6cc176fc7c26555020ff9663cbdR562