When working on the darwin stdenv I did not find the composition of the stages obvious. To help understand what is built and when I created this method of showing which packages are contributed by each phase.
The report contains all the of the derivations in the closure for
nix-instantiate -A hello grouped by the stdenv that built them. It's a rough
hueristic but succifiently effective.
It's not with some quirks, for example each stdenv appears twice. Once for
stdenv and once for stdenvNoCC.
See example-report.md.