[GHC] #13414: shebang + literate haskell causes line numbering skew

[GHC]

#13414: shebang + literate haskell causes line numbering skew
-------------------------------------+-------------------------------------
           Reporter:  slyfox         |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  low            |         Milestone:
          Component:  Compiler       |           Version:  8.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Incorrect
  Unknown/Multiple                   |  error/warning at compile-time
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 Noticed on doctest's Setup.lhs file. Minimal example:
 {{{#!hs
 #!/usr/bin/env runhaskell
 > main = return ()
 }}}

 {{{
 $ inplace/bin/ghc-stage2 -fforce-recomp -Wall Setup
 [1 of 1] Compiling Main             ( Setup.lhs, Setup.o )

 Setup.lhs:1:3: warning: [-Wmissing-signatures]
     Top-level binding with no type signature: main :: IO ()
   |
 1 | #!/usr/bin/env runhaskell
   |   ^^^^
 }}}

 Notice how it points 4 characters a line before '''main'''.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13414>
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