[GHC] #11464: Type casts cause confusing error

[GHC]

#11464: Type casts cause confusing error
-------------------------------------+-------------------------------------
        Reporter:  simonpj           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"b2e6350fb23403f1c88c5cfed5270d78dbdb6573/ghc" b2e6350/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="b2e6350fb23403f1c88c5cfed5270d78dbdb6573"
 Strip casts in checkValidInstHead

 This patch addresses Trac #11464.

 The fix is a bit crude (traverse the type to remove CastTys),
 but it's also simple.

 See Note [Casts during validity checking] in TcValidity
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11464#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler