[GHC] #9009: Confusing error message when loading package with TH

[GHC]

#9009: Confusing error message when loading package with TH
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       Reporter:  jstolarek         |             Owner:
           Type:  bug               |            Status:  new
       Priority:  normal            |         Milestone:
      Component:  Package system    |           Version:  7.8.2
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  Other
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
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 I got this error message when compiling a file that calls Template Haskell
 function from `singletons` package:

 {{{
 [1 of 1] Compiling Splices          ( Splices.hs, Splices.o )
 Loading package ghc-prim ... linking ... done.
 Loading package integer-gmp ... linking ... done.
 Loading package base ... linking ... done.
 Loading package transformers-0.3.0.0 ... linking ... done.
 Loading package pretty-1.1.1.1 ... linking ... done.
 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 mtl-2.1.2 ... linking ... done.
 Loading package template-haskell ... linking ... done.
 Loading package syb-0.4.1 ... linking ... done.
 Loading package th-desugar-1.4.0 ... linking ... done.
 Loading package singletons-1.0 ... <command line>: can't load .so/.DLL
 for: /home/killy/.cabal/lib/x86_64-linux-
 ghc-7.8.2/singletons-1.0/libHSsingletons-1.0-ghc7.8.2.so
 (/home/killy/.cabal/lib/x86_64-linux-
 ghc-7.8.2/singletons-1.0/libHSsingletons-1.0-ghc7.8.2.so: undefined
 symbol:
 singletonszm1zi0_DataziSingletonsziSingleziMonad_lookupProxy1_info)
 }}}

 After some investigation it turned out that the module
 Data.Singletons.Single.Monad was not listed in singletons.cabal file -
 neither under exported-modules nor other-modules - when the package was
 installed. The error message is mostly confusing. It would be good to at
 least get a hint on the possible cause.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9009>
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