[GHC] #10752: Print which warning-flag controls/enabled an emitted warning

[GHC]

#10752: Print which warning-flag controls/enabled an emitted warning
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        Reporter:  hvr               |                Owner:  barrucadu
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:
      Resolution:                    |             Keywords:
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):  Phab:D1943
       Wiki Page:  Design/Warnings   |
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Comment (by Herbert Valerio Riedel <hvr@…>):

 In [changeset:"b6c61e372a1a783b32f1bbd1ceb446e89478a138/ghc"
 b6c61e37/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="b6c61e372a1a783b32f1bbd1ceb446e89478a138"
 Print which flag controls emitted SafeHaskell warnings

 This is extends bb5afd3c274011c5ea302210b4c290ec1f83209c to cover
 SafeHaskell warnings.

 This implements yet another part of #10752
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10752#comment:19>
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