Is

from pants.base.build_environment import get_buildroot

a Pants™ approved way of getting the root of the monorepo in a plugin?

Thats the old v1 way For here, you will want to put the type

BuildRoot

in your

@rule

signature. See https://github.com/pantsbuild/pants/blob/c98ee3696818bc9945968ba94a14180d9466a6e7/src/python/pants/backend/project_info/filedeps.py#L82 and line 118