[GHC] #12955: Confusing error (module is not loaded) when more hsigs provided than -instantiated-with

[GHC]

#12955: Confusing error (module is not loaded) when more hsigs provided than
-instantiated-with
-------------------------------------+-------------------------------------
           Reporter:  ezyang         |             Owner:  ezyang
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.2.1
          Component:  Compiler       |           Version:  8.1
           Keywords:  backpack       |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 Steps to reproduce:

 1. Create an `A.hsig` file with `signature A where`
 2. Try to build it with `ghc --make A.hsig`

 Expected: Some error indicating an unexpected signature (you need to
 specify `-instantiated-with`

 Actual: This error:

 {{{
 [1 of 1] Compiling A[sig]           (.hsig -> .o)
 attempting to use module ‘main:A’ (A.hsig) which is not loaded
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12955>
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