[GHC] #13598: role annotation for newtype (partially?) ignored?

[GHC]

#13598: role annotation for newtype (partially?) ignored?
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        Reporter:  edsko             |                Owner:  (none)
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1-rc2
      Resolution:  invalid           |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by facundo.dominguez):

 To be fair, someone pointed to me recently that the haddock documentation
 of the [https://www.stackage.org/haddock/lts-8.12/ghc-prim-0.5.0.0/GHC-
 Types.html#t:Coercible Coercible] class already says something with
 respect to this:
 {{{
 The third kind of instance exists for every newtype NT = MkNT T and comes
 in two variants, namely

 instance Coercible a T => Coercible a NT
 instance Coercible T b => Coercible NT b

 This instance is only usable if the constructor MkNT is in scope.
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13598#comment:7>
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