[GHC] #10019: GHCi cannot reify a custom data constructor with Template Haskell on the first attempt

[GHC]

#10019: GHCi cannot reify a custom data constructor with Template Haskell on the
first attempt
-------------------------------------+-------------------------------------
              Reporter:              |             Owner:
  RyanGlScott                        |            Status:  new
                  Type:  bug         |         Milestone:
              Priority:  normal      |           Version:  7.8.4
             Component:  Template    |  Operating System:  Unknown/Multiple
  Haskell                            |   Type of failure:  GHC rejects
              Keywords:              |  valid program
          Architecture:              |        Blocked By:
  Unknown/Multiple                   |   Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
-------------------------------------+-------------------------------------
 I've uncovered an unusual bug with Template Haskell inside of GHCi. To
 duplicate it, load GHCi, create a data type, then attempt to reify one of
 its constructors. It will fail the first time, but succeed the second
 time.

 {{{
 $ ghci -XTemplateHaskell
 GHCi, version 7.8.4: http://www.haskell.org/ghc/  :? for help
 Loading package ghc-prim ... linking ... done.
 Loading package integer-gmp ... linking ... done.
 Loading package base ... linking ... done.
 λ> import Language.Haskell.TH
 λ> data Option a = Some a | None
 λ> $(reify 'Some >>= stringE . show)
 Failed to load interface for ‘Ghci1’
 no package matching ‘interactive’ was found
 λ> $(reify 'Some >>= stringE . show)
 Loading package array-0.5.0.0 ... linking ... done.
 Loading package deepseq-1.3.0.2 ... linking ... done.
 Loading package containers-0.5.5.1 ... linking ... done.
 Loading package pretty-1.1.1.1 ... linking ... done.
 Loading package template-haskell ... linking ... done.
 "DataConI Ghci1.Some (ForallT [PlainTV a_1627392303] [] (AppT (AppT ArrowT
 (VarT a_1627392303)) (AppT (ConT Ghci1.Option) (VarT a_1627392303))))
 Ghci1.Option (Fixity 9 InfixL)"
 }}}

 Curiously, this doesn't happen when you reify a data constructor in
 {{{base}}}, such as {{{Just}}}:

 {{{
 $ ghci -XTemplateHaskell
 GHCi, version 7.8.4: http://www.haskell.org/ghc/  :? for help
 Loading package ghc-prim ... linking ... done.
 Loading package integer-gmp ... linking ... done.
 Loading package base ... linking ... done.
 λ> import Language.Haskell.TH
 λ> $(reify 'Just >>= stringE . show)
 Loading package array-0.5.0.0 ... linking ... done.
 Loading package deepseq-1.3.0.2 ... linking ... done.
 Loading package containers-0.5.5.1 ... linking ... done.
 Loading package pretty-1.1.1.1 ... linking ... done.
 Loading package template-haskell ... linking ... done.
 "DataConI Data.Maybe.Just (ForallT [PlainTV a_1627398816] [] (AppT (AppT
 ArrowT (VarT a_1627398816)) (AppT (ConT Data.Maybe.Maybe) (VarT
 a_1627398816)))) Data.Maybe.Maybe (Fixity 9 InfixL)"
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10019>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler