Since there's still not support for gch-mod to work with GHC 8.2.1, this is a stack.yaml configuration that makes it work in Atom.
Make sure your resolver is set to:
resolver: lts-11.17
Add the following to extra-deps in stack.yaml:
extra-deps:
- https://hackage.haskell.org/package/ghc-mod-5.9.0.0/candidate/ghc-mod-5.9.0.0.tar.gz
- cabal-helper-0.8.0.2
- extra-1.5.3
- monad-journal-0.7.2
- optparse-applicative-0.13.2.0
- either-4.4.1.1
- free-4.12.4
- haskell-src-exts-1.19.1
- hlint-2.0.9
- haskell-src-exts-util-0.2.1
Then run:
$ stack build ghc-mod
and suddenly the Haskell linter in Atom should start working again.