[GHC] #6016: On Windows, runhaskell hits an error on UTF-8 files with a BOM

[GHC]

#6016: On Windows, runhaskell hits an error on UTF-8 files with a BOM
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              Reporter:  vsajip      |            Owner:
                  Type:  bug         |           Status:  patch
              Priority:  normal      |        Milestone:  7.10.1
             Component:  Compiler    |          Version:  7.0.4
  (Parser)                           |         Keywords:  BOM
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:  GHC         |  Related Tickets:  #1744
  rejects valid program              |
             Test Case:              |
              Blocking:              |
Differential Revisions:  Phab:D176   |
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Comment (by Austin Seipp <austin@…>):

 In [changeset:"9e939403241b758a685834c9ff62edcd3172a2cf/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="9e939403241b758a685834c9ff62edcd3172a2cf"
 StringBuffer should not contain initial byte-order mark (BOM)

 Summary:
 Just skipping over a BOM, but leaving it in the Stringbuffer, is not
 sufficient. The Lexer calls prevChar when a regular expression starts
 with '^' (which is a shorthand for '\n^'). It would never match on the
 first line, since instead of '\n', prevChar would still return '\xfeff'.

 Test Plan: validate

 Reviewers: austin, ezyang

 Reviewed By: austin, ezyang

 Subscribers: simonmar, ezyang, carter

 Differential Revision: https://phabricator.haskell.org/D176

 GHC Trac Issues: #6016
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/6016#comment:7>
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