[GHC] #12390: List rules for `Coercible` instances

[GHC]

#12390: List rules for `Coercible` instances
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:  newcomer
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 tellah):

 Newcomer here who has been poking around this a bit. From my initial
 impressions of the `:info` code, it would appear that the only place such
 an info string could be stored is in the TyThing. This is because the
 input string is converted String -> Name -> TyThing, and then the TyThing
 is converted to an IfaceDecl for printing.

 So then the question is: where does the suggested info string come from? I
 have some basic code that can store arbitrary text for `:info` but I am
 not sure what the front end for this should look like.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12390#comment:5>
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