haskell-process-load-file on a file with a relative import and a type error fails with "Unexpected response from haskell process" instead of showing the error

[rntz]

How to replicate: Make a directory with two files, A.hs and B.hs, like so:

-- In A.hs:
module A where {}
-- In B.hs:
import A
x = unbound -- or any other code that shouldn't typecheck

Then visit B.hs and run C-c C-l, that is, haskell-process-load-file.

Expected result: I get a nice error message in *haskell* telling me Variable not in scope: unbound.

Actual result: I get a message in the minibuffer saying: Haskell process command errored with: (error "Unexpected response from haskell process."), and no error message in *haskell*, so I am left not knowing what went wrong or how to fix it.

[rntz]

Revisiting this after 5 years, the example in the original post fails to reproduce the bug for me. However, other very similar cases generate the same problem. For instance:

import Data.Map
x = unbound

This may be the root cause of #1621 as well.

[rntz]

this may be fixed by #1850