[GHC] #11551: Get doctests into testsuite

[GHC]

#11551: Get doctests into testsuite
-------------------------------------+-------------------------------------
        Reporter:  lwm               |                Owner:
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Core Libraries    |              Version:  7.10.3
      Resolution:                    |             Keywords:
                                     |  documentation, doctest
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Documentation     |  Unknown/Multiple
  bug                                |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by phadej):

 you have to compile doctests against the same compiler you are testing
 with.

 - A compiled ghc master
 - patched ghc-paths: https://github.com/simonmar/ghc-paths/pull/9 (not
 sure if actually necessary)
 - compiled doctest using just compiled ghc
 - `.../build/doctest/doctest libraries/base/Data/Maybe.hs`
 - profit

 {{{
 Examples: 44  Tried: 44  Errors: 0  Failures: 0
 }}}

 Maybe, Char and Either pass, Functor got:

 {{{
 ### Failure in libraries/base/Data/Functor.hs:49: expression `show <$>
 Nothing'
 expected: "Nothing"
  but got: ""
           "\ESC[;1m<interactive>:31:6: \ESC[;1m\ESC[31merror:\ESC[;1m"
           "    Ambiguous occurrence \8216<$>\8217"
           "    It could refer to either \8216Data.Functor.<$>\8217,"
           "                             defined at
 libraries/base/Data/Functor.hs:73:1"
           "                          or \8216Prelude.<$>\8217,"
           "                             imported from \8216Prelude\8217
 (and originally defined in \8216Data.Functor\8217)\ESC[0m"
 }}}

 nasty colorcodes!

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11551#comment:4>
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