[GHC] #9693: Reloading GHCi with Template Haskell names can panic GHC

[GHC]

#9693: Reloading GHCi with Template Haskell names can panic GHC
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        Reporter:  maxs              |                Owner:
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:
       Component:  Template Haskell  |              Version:  7.8.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 Still reproducible on HEAD, but you'll need a different `Fun.hs`:

 {{{#!hs
 module Fun where
 import Language.Haskell.TH

 stuff = do
   -- let x = mkName "X"
   x <- newName "X"
   sequence $ [dataD (return []) x [] Nothing [
       normalC x []
     ] []]
 }}}

 And you'll get a slightly different error message:

 {{{
 λ> :r
 [1 of 2] Compiling Fun              ( Fun.hs, interpreted )
 [2 of 2] Compiling Main             ( thbug.hs, interpreted )
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.1.20161010 for x86_64-unknown-linux):
         kcLookupTcTyCon
   APromotionErr RecDataConPE
   Call stack:
       CallStack (from HasCallStack):
         prettyCurrentCallStack, called at
 compiler/utils/Outputable.hs:1076:58 in ghc:Outputable
         callStackDoc, called at compiler/utils/Outputable.hs:1080:37 in
 ghc:Outputable
         pprPanic, called at compiler/typecheck/TcHsType.hs:1656:27 in
 ghc:TcHsType

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

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9693#comment:6>
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