[GHC] #12361: Add -dppr-ribbon-cols

[GHC]

#12361: Add -dppr-ribbon-cols
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           Reporter:  ezyang         |             Owner:
               Type:  feature        |            Status:  new
  request                            |
           Priority:  low            |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:  easy           |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Right now, users can control the width of GHC error messages (`-dppr-
 ribbons-per-line`) but not the ratio of line length to ribbon length. The
 latter would be useful, because in some contexts a user might prefer error
 messages to be as densely packed as possible (ratio of 1.0).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12361>
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