Typeable solver regression

This bug is known and fixed in master. Simon and Austin and Iavor are all aware of it. This ticket exists to ensure that the fix doesn't get lost.

This code breaks under the Typeable solver in 7.10.1-rc3 and is fixed in master.

The relevant commit in master is 3a0019e3 : Improve Typeable solver.

{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE FlexibleContexts #-}
module Bug where

import Data.Typeable

newtype V n a = V [a]

class    Typeable a                   => C a
instance (Typeable (V n), Typeable a) => C (V n a)

-- Bug.hs:13:10:
--  Could not deduce (Typeable (V n a))
--    arising from the superclasses of an instance declaration
--  from the context (Typeable (V n), Typeable a)
--    bound by the instance declaration at Bug.hs:13:10-50
--  In the instance declaration for ‘C (V n a)’

Trac metadata

Trac field	Value
Version	7.10.1-rc3
Type	Bug
TypeOfFailure	OtherFailure
Priority	highest
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	diatchki
Operating system
Architecture