[GHC] #14365: Panic with (bogus?) deriving in hs-boot: newTyConEtadArity

[GHC]

#14365: Panic with (bogus?) deriving in hs-boot: newTyConEtadArity
-------------------------------------+-------------------------------------
        Reporter:  happykitten       |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:  deriving
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4102
       Wiki Page:                    |
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Changes (by RyanGlScott):

 * status:  new => patch
 * keywords:   => deriving
 * differential:   => Phab:D4102


Comment:

 Well that's embarrassing. The
 [http://git.haskell.org/ghc.git/blob/317aa966b3d89e45227a5870feba339e34d77a18:/docs/users_guide/separate_compilation.rst#l731
 GHC users' guide] states that you can't have derived instances in `.hs-
 boot` files, but clearly we weren't checking for this in practice.
 Phab:D4102 is an attempt to do so.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14365#comment:1>
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