[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:  (none)
            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 Ben Gamari <ben@…>):

 In [changeset:"fbe162f58caa31df445d9edbf0b0919810687011/ghc"
 fbe162f5/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="fbe162f58caa31df445d9edbf0b0919810687011"
 Add a broken test for lingering state from TH unique names #9693

 The stderr output is

 ```
 Loading with T9693_initial.hs

 T9693_main.hs:4:1:
     Same exact name in multiple name-spaces:
       type constructor or class ‘X’, declared at: T9693_main.hs:4:1
       data constructor ‘X’, declared at: T9693_main.hs:4:1
       Probable cause: you bound a unique Template Haskell name (NameU),
       perhaps via newName, in different name-spaces.
       If that's it, then -ddump-splices might be useful
 Reloading with T9693_modified.hs

 T9693_main.hs:1:1:
     Data constructor ‘X’ used as a type constructor
 ```

 The strange thing is that the modified version uses (mkName "X"), which
 should
 be fine for simultaneous use in both a data constructor and type
 constructor.
 Indeed, on a fresh load, the modified version works fine. So there is some
 sort
 of state left over from the prior load when (newName "X") was used.

 Test Plan: testsuite/tests/th/T9693.script

 Reviewers: bgamari, sighingnow, RyanGlScott

 Reviewed By: sighingnow, RyanGlScott

 Subscribers: RyanGlScott, sighingnow, rwbarton, thomie, carter

 Differential Revision: https://phabricator.haskell.org/D4926
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9693#comment:10>
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