Commit 1998b95adc6b5a9aef336e45955a01575bd898f1 “haskellPackages: update default compiler from ghc 8.10.2 to version 8.10.3” broke Agda because Agda.cabal incorrectly declares a transformers dependency only for ghc < 8.10.3: if impl(ghc >= 8.6.4) && impl(ghc < 8.10.3) build-depends: transformers == 0.5.6.2 if impl(ghc >= 8.4) && impl(ghc < 8.6.4) build-depends: transformers == 0.5.5.0 if impl(ghc < 8.4) build-depends: transformers == 0.5.2.0 leading to this error: src/full/Agda/Utils/Maybe.hs:13:1: error: Could not load module ‘Control.Monad.Trans.Maybe’ It is a member of the hidden package ‘transformers-0.5.6.2’. Perhaps you need to add ‘transformers’ to the build-depends in your .cabal file. Use -v (or `:set -v` in ghci) to see a list of the files searched for. | 13 | import Control.Monad.Trans.Maybe | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Signed-off-by: Anders Kaseorg <andersk@mit.edu>