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

[GHC]

#9693: Reloading GHCi with Template Haskell names can panic GHC
-------------------------------------+-------------------------------------
              Reporter:  maxs        |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Template    |          Version:  7.8.3
  Haskell                            |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:  GHC         |  Related Tickets:
  rejects valid program              |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
-------------------------------------+-------------------------------------
Changes (by thomie):

 * status:  infoneeded => new
 * component:  Compiler => Template Haskell


Comment:

 I am able to reproduce with 7.8.3 and recent HEAD, on Linux, following
 these steps:

 * ghci thbug.hs
 * ignore the error
 * comment out the newName, uncomment the mkName in Fun.hs
 * :r

 This is the result:
 {{{
 $ ghc-7.9.20141108 --interactive thbug.hs
 GHCi, version 7.9.20141108: http://www.haskell.org/ghc/  :? for help
 [1 of 2] Compiling Fun              ( Fun.hs, interpreted )
 [2 of 2] Compiling Main             ( thbug.hs, interpreted )

 thbug.hs:4:1:
     Duplicate exact Name ‘X’
       Probable cause: you used a unique Template Haskell name (NameU),
       perhaps via newName, but bound it multiple times
       If that's it, then -ddump-splices might be useful
 Failed, modules loaded: Fun.

 ...
 Comment out the newName, uncomment the mkName in Fun.hs.
 ...

 *Fun> :r
 [1 of 2] Compiling Fun              ( Fun.hs, interpreted )
 [2 of 2] Compiling Main             ( thbug.hs, interpreted )
 ghc: panic! (the 'impossible' happened)
   (GHC version 7.9.20141108 for x86_64-unknown-linux):
         kcLookupKind APromotionErr RecDataConPE
 }}}

 So the first 'duplicate exact name X' error leaves GHCi in some
 inconsistent state.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9693#comment:2>
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