[GHC] #999: Misattributed parse error in do block

[GHC]

#999: Misattributed parse error in do block
--------------------------------+-------------------------------------------
 Reporter:  red5_2 at hotmail.com  |          Owner:                  
     Type:  bug                 |         Status:  new             
 Priority:  normal              |      Milestone:  _|_             
Component:  Compiler (Parser)   |        Version:  6.4.2           
 Severity:  normal              |     Resolution:                  
 Keywords:                      |     Difficulty:  Moderate (1 day)
 Testcase:                      |   Architecture:  Unknown         
       Os:  Unknown             |  
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Changes (by simonmar):

  * difficulty:  Unknown => Moderate (1 day)
  * milestone:  => _|_

Comment:

 This happens because the closing bracket ends the layout for the do-block,
 via Haskell's parse-error layout convention.  This causes the do-block to
 be checked, before getting back to parsing the rest of the file.

 If you use `-ferror-spans`, then you get the position of the start and end
 of the statement.

 To fix this we would probably have to postpone checking the syntax of a
 do-expression until the renamer.  This isn't easy, because the `HsDo`
 constructor already has separate fields for statements and "body"
 (although I'm not sure why).

 This bug is very closely related to #984.  I'll leave it low prio for now.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/999>
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