ghc-8.0.1: panic! (the 'impossible' happened) filterImports/combine (double import)

It's a distilled example or repa-devil-0.3.2.6 build failure:

-- Cursored.hs:
{-# LANGUAGE TypeFamilies #-}
module Cursored where

class Source r where
    data Array r

instance Source () where
    data Array () = F { f :: Int }

-- Bug.hs:
module DevIL () where

import Cursored (Array(..), Source(..))

[1 of 2] Compiling Cursored         ( Cursored.hs, Cursored.o )
[2 of 2] Compiling DevIL            ( Bug.hs, Bug.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 8.0.1 for x86_64-unknown-linux):
        filterImports/combine
  (Array, Array{Array, F, f}, Nothing)
  (Array, Source{Source, Array}, Nothing)

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

The error is the same as #11959 (closed) but involved entities are slightly different.

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed weight to 5

added Tbug Trac import labels

changed milestone to %8.0.2

changed weight to 7

Regression from GHC 7.10.3.

Trac metadata

Trac field	Value
Priority	normal → high

mentioned in issue #12216 (closed)

mentioned in commit 393928db

Simple fix, could merge.

simon

Trac metadata

Trac field	Value
Test case	- → rename/should_compile/T12127

added 1 deleted label

closed

Merged to ghc-8.0 as 8736625f.

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed

removed 1 deleted label

mentioned in issue #12604 (closed)

mentioned in issue #13089 (closed)

added Phigh label