[GHC] #12395: Misleading GHCi errors when package is installed

[GHC]

#12395: Misleading GHCi errors when package is installed
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        Reporter:  crockeea          |                Owner:
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:
       Component:  GHCi              |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  warning at compile-time            |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #11536            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by crockeea):

 My current workflow requires using `cabal install`, and I'm not aware of
 another option (though I'm open to suggestions. I'm not sure if this
 problem occurs with stack or not, but either way stack still doesn't have
 an LTS resolver for GHC 8.0.) I wrote a library, and also a separate
 program which depends on that library. Thus the library must be cabal-
 installed to build the second program (this is true even if I use `add-
 source` in cabal). Then when I go back to make changes to the library, the
 error above can occur.

 Note that in this workflow, it is never necessary to `ghc-pkg unregister`
 the library: if I build with cabal, it detects the changed source and
 automatically rebuilds/installs, and if I use ghci it uses the source
 code.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12395#comment:4>
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