Infinite loop during error reporting (ignores SIGINT/SIGTERM, then OOMs)

Compiling the repro snippet produces the following incomplete output and hangs GHC:

$ ghc repro.hs
[1 of 1] Compiling Main             ( repro.hs, repro.o )

repro.hs:16:22: error:

The GHC process ignores SIGINT -- so it must be killed with SIGKILL. The memory usage grows, until it consumes all memory (~30G RAM + swap) and is terminated by the OOM killer.

This minimal snippet depends on generics-sop (tested with version 0.4.0.0). Sadly I didn't find a constraint in base to cause this behavior..

{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE TypeFamilies #-}

import Generics.SOP (HasDatatypeInfo)

data family   TF i a :: *
data instance TF i a = R

class C i a where
  method :: TF i a

instance C i () where

instance HasDatatypeInfo a => C i a where
  method = undefined function

function :: C i a => TF i a
function = method

main = undefined

Affects 8.4.3 and 8.6.1.

Not tested on 8.6.2 & 8.6.3.