/usr/share/doc/r-cran-rlang/tests/testthat/fixtures/rlanglibtest/src/Makevars is in r-cran-rlang 0.2.0-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1
PKG_CPPFLAGS = -I./lib/