runInterpreter regression in 0.9.0.6 for GHC < 9.2

[brandon-leapyear]

runInterpreter in 0.9.0.6 with GHC < 9.2 on a module that fails to compile will send errors to stderr and return Left (UnknownError "Got no error message") instead of Left (WontCompile ...).

This currently fails with vanilla lts-19.11, but I wanted to verify across GHC versions as well. This is the script I used to test this:

for hint_version in 0.9.0.5 0.9.0.6; do
  for ghc_version in 8.10 9.0 9.2; do
    echo "##########################"
    echo "hint: ${hint_version}, ghc: ${ghc_version}";
    echo -e "import Language.Haskell.Interpreter\nrunInterpreter $ loadModules [\"Foo.hs\"]" | stack ghci --resolver lts-19.11 --package hint-${hint_version} --compiler ghc-${ghc_version}
  done
done

on this file:

x :: Int
x = ()

##########################
hint: 0.9.0.5, ghc: 8.10
[...]
Left (WontCompile [GhcError {errMsg = "Foo.hs:2:5: error:\n    \8226 Couldn't match expected type \8216Int\8217 with actual type \8216()\8217\n    \8226 In the expression: ()\n      In an equation for \8216x\8217: x = ()"},GhcError {errMsg = "Foo.hs:2:5: error:\n    \8226 Couldn't match expected type \8216Int\8217 with actual type \8216()\8217\n    \8226 In the expression: ()\n      In an equation for \8216x\8217: x = ()"}])
[...]
##########################
hint: 0.9.0.5, ghc: 9.0
[...]
Left (WontCompile [GhcError {errMsg = "Foo.hs:2:5: error:\n    \8226 Couldn't match expected type \8216Int\8217 with actual type \8216()\8217\n    \8226 In the expression: ()\n      In an equation for \8216x\8217: x = ()"},GhcError {errMsg = "Foo.hs:2:5: error:\n    \8226 Couldn't match expected type \8216Int\8217 with actual type \8216()\8217\n    \8226 In the expression: ()\n      In an equation for \8216x\8217: x = ()"}])
[...]
##########################
hint: 0.9.0.5, ghc: 9.2
[...]
Left (WontCompile [GhcError {errMsg = "Foo.hs:2:5: error:\n    \8226 Couldn't match expected type \8216Int\8217 with actual type \8216()\8217\n    \8226 In the expression: ()\n      In an equation for \8216x\8217: x = ()"},GhcError {errMsg = "Foo.hs:2:5: error:\n    \8226 Couldn't match expected type \8216Int\8217 with actual type \8216()\8217\n    \8226 In the expression: ()\n      In an equation for \8216x\8217: x = ()"}])
[...]
##########################
hint: 0.9.0.6, ghc: 8.10
[...]
Foo.hs:2:5: error:
    • Couldn't match expected type ‘Int’ with actual type ‘()’
    • In the expression: ()
      In an equation for ‘x’: x = ()
  |
2 | x = ()
  |     ^^

Foo.hs:2:5: error:
    • Couldn't match expected type ‘Int’ with actual type ‘()’
    • In the expression: ()
      In an equation for ‘x’: x = ()
  |
2 | x = ()
  |     ^^
Left (UnknownError "Got no error message")
[...]
##########################
hint: 0.9.0.6, ghc: 9.0
[...]
Foo.hs:2:5: error:
    • Couldn't match expected type ‘Int’ with actual type ‘()’
    • In the expression: ()
      In an equation for ‘x’: x = ()
  |
2 | x = ()
  |     ^^

Foo.hs:2:5: error:
    • Couldn't match expected type ‘Int’ with actual type ‘()’
    • In the expression: ()
      In an equation for ‘x’: x = ()
  |
2 | x = ()
  |     ^^
Left (UnknownError "Got no error message")
[...]
##########################
hint: 0.9.0.6, ghc: 9.2
[...]
Left (WontCompile [GhcError {errMsg = "Foo.hs:2:5: error:\n    \8226 Couldn't match expected type \8216Int\8217 with actual type \8216()\8217\n    \8226 In the expression: ()\n      In an equation for \8216x\8217: x = ()"},GhcError {errMsg = "Foo.hs:2:5: error:\n    \8226 Couldn't match expected type \8216Int\8217 with actual type \8216()\8217\n    \8226 In the expression: ()\n      In an equation for \8216x\8217: x = ()"}])
[...]