-Wall-missed-specialisations warnings not fatal with -Werror

When compiling a program with GHC 8.4.3, vector 0.12.0.1 (with a dependency on primitive 0.6.4.0) and -Wall-missed-specialisations -Werror, warnings are produced, but they aren't fatal. -Werror should make them fatal but doesn't.

A somewhat-minimal example:

{-# OPTIONS_GHC -Wall-missed-specialisations -Werror #-}
{-# LANGUAGE MultiParamTypeClasses, TypeFamilies #-}

module Warnings3 where

import GHC.Base (liftM)
import qualified Data.Vector.Generic.Base as G (Vector, basicUnsafeFreeze,
  basicUnsafeThaw, basicLength, basicUnsafeSlice, basicUnsafeIndexM,
  basicUnsafeCopy, elemseq)
import qualified Data.Vector.Generic.Mutable.Base as GM (MVector, basicLength,
  basicUnsafeSlice, basicOverlaps, basicUnsafeNew, basicInitialize,
  basicUnsafeReplicate, basicUnsafeRead, basicUnsafeWrite, basicClear, basicSet,
  basicUnsafeCopy, basicUnsafeMove, basicUnsafeGrow)
import qualified Data.Vector.Unboxed as U (Unbox, Vector)
import qualified Data.Vector.Unboxed.Mutable as U (MVector)

newtype T = T () deriving (Show, Eq, Ord)
newtype C = C (U.Vector T) deriving (Show, Eq, Ord)

instance U.Unbox T

newtype instance U.MVector s T = MV_T (U.MVector s ())
instance GM.MVector U.MVector T where
  basicLength (MV_T mv) = GM.basicLength mv
  basicUnsafeSlice i l (MV_T mv) = MV_T (GM.basicUnsafeSlice i l mv)
  basicOverlaps (MV_T mv1) (MV_T mv2) = GM.basicOverlaps mv1 mv2
  basicUnsafeNew l = MV_T `liftM` GM.basicUnsafeNew l
  basicInitialize (MV_T mv) = GM.basicInitialize mv
  basicUnsafeReplicate l _ = MV_T `liftM` GM.basicUnsafeReplicate l ()
  basicUnsafeRead (MV_T mv) i = const (T ()) `liftM` GM.basicUnsafeRead mv i
  basicUnsafeWrite (MV_T mv) i _ = GM.basicUnsafeWrite mv i ()
  basicClear (MV_T mv) = GM.basicClear mv
  basicSet (MV_T mv) x = GM.basicSet mv ()
  basicUnsafeCopy (MV_T mv1) (MV_T mv2) = GM.basicUnsafeCopy mv1 mv2
  basicUnsafeMove (MV_T mv1) (MV_T mv2) = GM.basicUnsafeMove mv1 mv2
  basicUnsafeGrow (MV_T mv) l = MV_T `liftM` GM.basicUnsafeGrow mv l

newtype instance U.Vector T = V_T (U.Vector ())
instance G.Vector U.Vector T where
  basicUnsafeFreeze (MV_T mv) = V_T `liftM` G.basicUnsafeFreeze mv
  basicUnsafeThaw (V_T v) = MV_T `liftM` G.basicUnsafeThaw v
  basicLength (V_T v) = G.basicLength v
  basicUnsafeSlice i l (V_T v) = V_T (G.basicUnsafeSlice i l v)
  basicUnsafeIndexM (V_T v) i = const (T ()) `liftM` G.basicUnsafeIndexM v i
  basicUnsafeCopy (MV_T mv) (V_T v) = G.basicUnsafeCopy mv v
  elemseq (V_T v) _ = G.elemseq v ()

The warnings are:

src/Warnings3.hs: warning:
    Could not specialise imported function ‘Data.Vector.Unboxed.$w$cshowsPrec’
      when specialising ‘Data.Vector.Unboxed.$fShowVector_$cshowsPrec’
    Probable fix: add INLINABLE pragma on ‘Data.Vector.Unboxed.$w$cshowsPrec’

src/Warnings3.hs: warning:
    Could not specialise imported function ‘Data.Vector.Unboxed.$fOrdVector_$cmin’
    Probable fix: add INLINABLE pragma on ‘Data.Vector.Unboxed.$fOrdVector_$cmin’

src/Warnings3.hs: warning:
    Could not specialise imported function ‘Data.Vector.Unboxed.$fOrdVector_$cmax’
    Probable fix: add INLINABLE pragma on ‘Data.Vector.Unboxed.$fOrdVector_$cmax’

Trac metadata

Trac field	Value
Version	8.4.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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