[GHC] #11219: Implement fine-grained `-Werror=...` facility

[GHC]

#11219: Implement fine-grained `-Werror=...` facility
-------------------------------------+-------------------------------------
           Reporter:  hvr            |             Owner:  quchen
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:  8.2.1
          Component:  Compiler       |           Version:
           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:  Design/Warnings
-------------------------------------+-------------------------------------
 ...copied from Design/Warnings:

 Introduce variant of `-Werror` (c.f. GCC's `-Werror=*`) which allows to
 specify the individual warnings to be promoted to errors, e.g.

      - `-Wall -Werror=orphans` would only promote `-Worphans` warnings
 into errors
      - `-Wall -Werror -Wno-error=missing-methods` would promote all
 warnings //except// `-Wmissing-methods` into errors

 TODO: specify semantics a bit more exactly (the basic idea is to follow
 gcc/clang as much as sensible, and only deviate where it's necessary)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11219>
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