Fix backpack typechecking with -j
Motivation
Currently, backpack typechecking is not supported with -j
as seen here.
This rather drastically increases compile times for large projects using backpack. It has not been revisited since the original backpack merge.
Proposal
Enable backpack typechecking with -j
, addressing whatever attendant issues caused this initial restriction. @ezyang expressed willingness to help out at least at a mentor level.