Panic in tcSimplifyRuleLhs

With this module, both 6.8.3 and the HEAD panic in tcSimplifyRuleLhs:

{-# LANGUAGE Rank2Types, ScopedTypeVariables #-}
module Foo where

foo :: (forall m. Monad m => Maybe (m a) -> Maybe (m a)) -> Maybe a -> Maybe a
foo _ x = x

{-# RULES

"foo/foo"
  forall (f :: forall m. Monad m => Maybe (m a) -> Maybe (m a))
         (g :: forall m. Monad m => Maybe (m b) -> Maybe (m b)) x.
  foo f (foo g x) = foo (f . g) x
 #-}

Note that the rule is incorrectly typed; with the correct types, no panic happens.

Incidentially, I'm not sure if ScopedTypeVariables should be required here.

Trac metadata

Trac field	Value
Version	6.8.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown
Architecture	Unknown