[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:"bb5afd3c274011c5ea302210b4c290ec1f83209c/ghc" bb5afd3/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="bb5afd3c274011c5ea302210b4c290ec1f83209c"
 Print which warning-flag controls an emitted warning

 Both gcc and clang tell which warning flag a reported warning can be
 controlled with, this patch makes ghc do the same. More generally, this
 allows for annotated compiler output, where an optional annotation is
 displayed in brackets after the severity.

 This also adds a new flag `-f(no-)show-warning-groups` to control
 whether to show which warning-group (such as `-Wall` or `-Wcompat`)
 a warning belongs to. This flag is on by default.

 This implements #10752

 Reviewed By: quchen, bgamari, hvr

 Differential Revision: https://phabricator.haskell.org/D1943
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10752#comment:15>
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