add_build_file_dep()function is used to mark a parse-time dependency onto another file, to make sure the Buck's internal caches invalidate build files correctly if that file is modified.
- The first and only argument is a path. As with
include_defs(), it looks similar to a build target because it starts with
//(indicating the root of the project), but is not a proper build target because it identifies a file relative to the root of the project rather than a build rule.