[R] Extra features not found when Arrow is detected with pkg

[westonpace]

Describe the bug, including details regarding any error messages, version, and platform.

I am well beyond my depth here but I was having trouble getting R to detect that my Arrow build had the datasets feature enabled (I don't normally build R but built it recently to debug an issue and ran into this).

I get the message echo "*** Arrow C++ libraries found via pkg-config at $FOUND_LIB_DIR" so R is finding Arrow that way. However, later, it seems to want to find the extra features in this way:

  # Check for features
  ARROW_OPTS_CMAKE="$LIB_DIR/cmake/Arrow/ArrowOptions.cmake"

  arrow_built_with() {
    # Function to check cmake options for features
    grep -i 'set('"$1"' "ON")' $ARROW_OPTS_CMAKE >/dev/null 2>&1
  }

Since LIB_DIR is unset it does not find the ArrowOptions.cmake file (even though I have one and it is installed). I have a fix that sets LIB_DIR in the pkg-config path and will create a PR but I have no idea if that is the best fix.

Component(s)

R