[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
      Resolution:                    |         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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Description changed by tibbe:

Old description:

> 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.)

New description:

 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#comment:2>
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