[GHC] #13746: Typeable changes in base-4.10 break ChasingBottoms's test suite

[GHC]

#13746: Typeable changes in base-4.10 break ChasingBottoms's test suite
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           Reporter:  refold         |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:                 |           Version:  8.2.1-rc2
  libraries/base                     |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Runtime crash
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 When compiled against base-4.10, `ChasingBottoms`'s test suite fails with:

 {{{
 Approx:
 ChasingBottomsTestSuite: typeRepTyCon: FunTy
 CallStack (from HasCallStack):
   error, called at libraries/base/Data/Typeable/Internal.hs:308:33 in
 base:Data.Typeable.Internal
 }}}

 This is due to the use of `error` in the following function in
 [https://github.com/ghc/ghc/blob/master/libraries/base/Data/Typeable/Internal.hs#L308
 `Data.Typeable.Internal`]:

 {{{#!hs
 -- | Observe the type constructor of a type representation
 typeRepTyCon :: TypeRep a -> TyCon
 typeRepTyCon (TrTyCon _ tc _) = tc
 typeRepTyCon (TrApp _ a _)    = typeRepTyCon a
 typeRepTyCon (TrFun _ _ _) = error "typeRepTyCon: FunTy" -- TODO
 }}}

 `ChasingBottoms`'s test suite works fine when compiled with GHC 8.0.2. It
 seems to me that the change in behaviour constitutes a bug or a breaking
 change (for which there is no mention in the changelog).

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13746>
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