[GHC] #3384: Add HsSyn prettyprinter tests

[GHC]

#3384: Add HsSyn prettyprinter tests
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        Reporter:  igloo             |                Owner:
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:  ⊥
       Component:  Test Suite        |              Version:
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by alanz):

 Updating https://github.com/alanz/ghc-exactprint/blob/no-
 annotations/tests/Test/NoAnnotations.hs#L119 to be

 {{{#!hs
   let !printed = pragmaStr ++ "\n" ++ (showSDoc_ $ GHC.ppr parsedOrig)
 }}}

 i.e. to simply `ppr` the `ParsedSource` and compare the resulting re-
 parsed AST.

 The initial results are for ghc-8.0.1, of the 823 test cases in ghc-
 exactprint, the straight GHC ppr fails to roundtrip 106 where it cannot be
 reparsed, and another 84 where the re-parsed AST does not match the
 original.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3384#comment:7>
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