Overall we're quite close to being able to build with GHC 9.
After this patch the biggest obstacle is that
regex-compat-tdfa doesn't build:
https://hub.darcs.net/shelarcy/regex-compat-tdfa/issue/2
1 patch for repository darcs-unstable@darcs.net:screened:
patch 821fbe1391f263d5becc87e1dea077a46f1eb2ba
Author: Ganesh Sittampalam <ganesh@earth.li>
Date: Sat May 15 15:55:25 BST 2021
* fix GHC 9.0 compile error
I suspect that it was caused by the changes to
impredicativity in GHC 9.