John Ericson authored Feb 02, 2020 and Marge Bot committed Feb 03, 2020

I found the old control flow a bit hard to follow; I rewrote it to first
decide whether to desugar, and then use that choice when computing
whether to simplify / what sort of interface file to write.

I hope eventually we will always write post-tc interface files, which
will make the logic of this function even simpler, and continue the
thrust of this refactor.