[GHC] #8710: Overlapping patterns warning misplaced

[GHC]

#8710: Overlapping patterns warning misplaced
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        Reporter:  goldfire          |                Owner:
            Type:  bug               |               Status:  new
        Priority:  low               |            Milestone:
       Component:  Compiler          |              Version:  7.7
      Resolution:                    |             Keywords:
                                     |  PatternMatchWarnings
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  warning at compile-time            |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by gkaracha):

 Replying to [comment:3 thomie]:
 > I would maybe prefer separate warnings, such that even for a single
 redundant clause, the warning message doesn't have to mention two
 different line numbers (one for the location of the whole match, and one
 for the location of the redundant clause).
 >
 > I don't know if there is precedent for multiple line numbers in a
 warning message.
 >
 > Either way is fine though.

 I created a small patch for this (Phab:D1910). If we print a separate
 warning for every redundant
 clause it may become overwhelming so I thought that it would be best to
 keep them all in the same
 warning. The patch has the following behavior:
 {{{
 Bug.hs:22:3: warning:
     Pattern match(es) are overlapped
     In an equation for ‘show’:
         len _     = ... (at Bug.hs:24:3)
         len _     = ... (at Bug.hs:25:3)
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8710#comment:5>
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