[GHC] #13664: Ill formatted warning about tabulators

[GHC]

#13664: Ill formatted warning about tabulators
-------------------------------------+-------------------------------------
           Reporter:  Lemming        |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.1-rc1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 GHC-8.2.0.20170505 does not format warnings about tabulators very well.
 It seems to use the tab character for formatting, which yields too few
 spaces when formatted,
 and in turn too many characters are colored.
 (It is hard to present the problem in this ticket, though.)
 {{{
 $ cat Tabulator.hs
 module Tabulator where

 x :: Int
 x =
         1*2*3*4*5*6*7*8*9
 -- we use a tab for indentation here

 $ ghc-8.2.0.20170505 -Wall Tabulator.hs
 [1 of 1] Compiling Tabulator        ( Tabulator.hs, Tabulator.o )

 Tabulator.hs:5:1: warning: [-Wtabs]
     Tab character found here.
     Please use spaces instead.
   |
 5 |     1*2*3*4*5*6*7*8*9
   | ^^^^^^^^
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13664>
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