[GHC] #12660: singletons doesn't compile with GHC 8.0.2 snapshot

[GHC]

#12660: singletons doesn't compile with GHC 8.0.2 snapshot
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        Reporter:  bgamari           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.0.2
       Component:  Compiler          |              Version:
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Trying to reproduce this.  But when I try `cabal install singletons` (with
 the HEAD ghc) I get
 {{{
 [3 of 8] Compiling Language.Haskell.TH.Desugar.Core (
 Language\Haskell\TH\Desugar\Core.hs,
 dist\build\Language\Haskell\TH\Desugar\Core.o )

 Language\Haskell\TH\Desugar\Core.hs:713:21: error:
     Ambiguous occurrence    Newtype
     It could refer to either    Language.Haskell.TH.Syntax.Newtype   ,
                              imported from    Language.Haskell.TH.Syntax
 at Language\Haskell\TH\Desugar\Core.hs:18:1-47
                           or    Language.Haskell.TH.Desugar.Core.Newtype
 ,
                              defined at
 Language\Haskell\TH\Desugar\Core.hs:108:18

 Language\Haskell\TH\Desugar\Core.hs:764:25: error:
     Ambiguous occurrence    Newtype
     It could refer to either    Language.Haskell.TH.Syntax.Newtype   ,
                              imported from    Language.Haskell.TH.Syntax
 at Language\Haskell\TH\Desugar\Core.hs:18:1-47
                           or    Language.Haskell.TH.Desugar.Core.Newtype
 ,
                              defined at
 Language\Haskell\TH\Desugar\Core.hs:108:18
 }}}
 What am I doing wrong?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12660#comment:5>
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