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

[GHC]

#14365: Panic with (bogus?) deriving in hs-boot: newTyConEtadArity
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           Reporter:  happykitten    |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 {{{
 $ cat A.hs
 module Main where

 import {-# SOURCE #-} B

 main = return ()
 $ cat B.hs
 module B where

 data Foo a = Foo a
   deriving (Functor)
 $ cat B.hs-boot
 module B where

 data Foo a
   deriving (Functor)
 $ ghc --make A.hs
 [1 of 3] Compiling B[boot]          ( B.hs-boot, B.o-boot )
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.2.1 for i386-unknown-linux):
         newTyConEtadArity
   Foo
   Call stack:
       CallStack (from HasCallStack):
         prettyCurrentCallStack, called at
 compiler/utils/Outputable.hs:1133:58 in ghc:Outputable
         callStackDoc, called at compiler/utils/Outputable.hs:1137:37 in
 ghc:Outputable
         pprPanic, called at compiler/types/TyCon.hs:2149:27 in ghc:TyCon

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 }}}

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