Unfortunately my first attempt in f14b6ea broke the evaluation and was
therefore reverted in 4419a31. I couldn't reproduce the error locally
but as @grahamc noted I shouldn't have imported from a derivation.
Thanks @joachifm and @grahamc for spotting the evaluation error and
reverting f14b6ea.
This reverts commit f14b6ea81f1739a90c208fbbdd1ed6f948434693.
This commit added IFD to Nixpkgs, where
Nixpkgs should be IFD-free. (Import
from derivation.)