Fix panic for `ByteArray#` arguments in CApiFFI foreign imports

Declarations such as

  foreign import capi  unsafe "string.h strlen"
      c_strlen_capi :: ByteArray# -> IO CSize

  foreign import capi  unsafe "string.h memset"
      c_memset_capi :: MutableByteArray# s -> CInt -> CSize -> IO ()

would cause GHC to panic because the CApiFFI c-wrapper generator didn't
know what C type to use for `(Mutable)ByteArray#` types (unlike the
`ccall` codepath).

This addresses #9274

Reviewed By: bgamari

Differential Revision: https://phabricator.haskell.org/D4092

1 files changed, 6 insertions, 0 deletions

diff --git a/compiler/deSugar/DsForeign.hs b/compiler/deSugar/DsForeign.hs
index 01173c932d..492d353cc0 100644
--- a/compiler/deSugar/DsForeign.hs
+++ b/compiler/deSugar/DsForeign.hs
@@ -717,6 +717,12 @@ toCType = f False
            -- through one layer of type synonym etc.
            | Just t' <- coreView t
               = f voidOK t'
+           -- This may be an 'UnliftedFFITypes'-style ByteArray# argument
+           -- (which is marshalled like a Ptr)
+           | Just byteArrayPrimTyCon        == tyConAppTyConPicky_maybe t
+              = (Nothing, text "const void*")
+           | Just mutableByteArrayPrimTyCon == tyConAppTyConPicky_maybe t
+              = (Nothing, text "void*")
            -- Otherwise we don't know the C type. If we are allowing
            -- void then return that; otherwise something has gone wrong.
            | voidOK = (Nothing, text "void")