[GHC] #9114: Invalid UTF8 not round-tripped correctly

[GHC]

#9114: Invalid UTF8 not round-tripped correctly
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       Reporter:  nomeata           |             Owner:
           Type:  bug               |            Status:  new
       Priority:  normal            |         Milestone:
      Component:  libraries/base    |           Version:  7.6.3
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
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 As reported by Robert Bihlmeyer at http://bugs.debian.org/748125, the
 promised round-tripping of invalid UTF8 sequences in filenames through
 String does not work:

 ```
 $ mkdir foo
 $ touch foo/$(echo -e '\xC0\xB7.txt')
 $ ghc -e 'System.Directory.getDirectoryContents "foo" >>= print . last'
 "7.txt"
 ```

 The sequence 0xC8B7 is an (invalid) encoding of 37, i.e. `'7'`, so if it
 is mapped to `'7'`, no round-tripping is possible. (Other invalid byte
 sequences are round-tripped.)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9114>
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