[GHC] #13254: Confusing error message from GHCI - "defined in multiple files" shows the same file

9 Feb 2017

      #13254: Confusing error message from GHCI - "defined in multiple files" shows the
same file
-------------------------------------+-------------------------------------
           Reporter:  ocharles       |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  GHCi           |           Version:  8.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 I just had the following very confusing exchange with GHCI:

 {{{
 λ :load
 Ok, modules loaded: none.

 λ :load src/Application/Aws.hs
 Ok, modules loaded: Application.Aws (dist/build/Application/Aws.o).

 λ private
 <interactive>:3:1: error: Variable not in scope: private

 λ :m *Application.Aws
 module 'Application.Aws' is not interpreted; try ':add *Application.Aws'
 first

 λ :add *Application.Aws
 <no location info>: error:
     module ‘circuithub-api-0.0.4-EeGo4QUTODrB58BZrr3htj:Application.Aws’
 is defined in multiple files: src/Application/Aws.hs
 src/Application/Aws.hs
 Failed, modules loaded: Application.Aws (dist/build/Application/Aws.o).

 λ :! ghc --version
 The Glorious Glasgow Haskell Compilation System, version 8.1.20161115
 }}}

 This can really be simplified to

 {{{
 λ :load src/Application/Aws.hs
 Ok, modules loaded: Application.Aws (dist/build/Application/Aws.o).

 λ :add *Application.Aws
 <no location info>: error:
     module ‘circuithub-api-0.0.4-EeGo4QUTODrB58BZrr3htj:Application.Aws’
 is defined in multiple files: src/Application/Aws.hs
 src/Application/Aws.hs
 Failed, modules loaded: Application.Aws (dist/build/Application/Aws.o).
 }}}

 For the record, here is Application.Aws:

 {{{#!hs
 {-# LANGUAGE DeriveDataTypeable #-}

 module Application.Aws
   ( AwsExtra(..)
   ) where

 import           Prelude

 import           Data.Data (Data)
 import           Data.ByteString.Char8
 import           Data.Text

 data AwsExtra = AwsExtra
   { awsKey            :: ByteString
   , awsSecret         :: ByteString
   , awsS3AssetsBucket :: Text
   } deriving (Show,Data)

 private :: Int
 private = 42
 }}}

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13254
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler