[GHC] #11786: Need -fno-print-explicit-runtime-reps to work on IfaceType, else RuntimeRep leaks

[GHC]

#11786: Need -fno-print-explicit-runtime-reps to work on IfaceType, else RuntimeRep
leaks
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           Reporter:  simonpj        |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  7.10.3
           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:
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 After #11549, we are suppose not to show `RuntimeRep` to users, when
 `-fno-print-explicit-runtime-reps` is on.  But we do:
 {{{
 :info ($)
 Prelude> :i ($)
 ($) ::  forall (r :: GHC.Types.RuntimeRep) a (b :: TYPE r).
         (a -> b) -> a -> b
         -- Defined in ‘GHC.Base’
 }}}
 This happens because the runtime-rep-suppression happens on `Type`, but
 for `:info` we use `pprInfo` which uses `tyThingToIfaceDecl` and then
 prints it. And `tyThingToIfaceDecl` doesn't know about the `-fprint-
 explicit-runtime-reps` flag; and I'd like to keep it that way.

 We want to change `pprType` to convert to `IfaceType` and then print
 anyway.

 I suppose that this means that the pretty-printer for `IfaceType` needs to
 know about this runtime-rep suppression.  That's a bit tiresome, but not
 impossible, especially since there is no shadowing to worry about.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11786>
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