[GHC] #15862: Typeable panic with promoted rank-2 kind (initDs)

[GHC]

#15862: Typeable panic with promoted rank-2 kind (initDs)
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.6.1
      Resolution:                    |             Keywords:  Typeable
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 Replying to [comment:1 goldfire]:
 > I would fix the missing impredicativity check before worrying about
 `initDs`.

 In case you didn't notice this, I deliberately enabled
 `ImpredicativeTypes` in this program :)

 I, too, am surprised that this panics, though. Especially since
 `typeIsTypeable` appears to
 [http://git.haskell.org/ghc.git/blob/1a3b9bd0b674ad16a41b942c738b8f34564bcd8d:/compiler/typecheck/TcTypeable.hs#l440
 already answer "no"] when a type contains a nested `forall` like this:

 {{{#!hs
 typeIsTypeable (ForAllTy{})         = False
 }}}

 It's possible that something else is going wrong, though.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15862#comment:2>
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