[GHC] #14597: Consider removing uses of unsafeGlobalDynFlags for -dppr-debug

[GHC]

#14597: Consider removing uses of unsafeGlobalDynFlags for -dppr-debug
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           Reporter:  bgamari        |             Owner:  (none)
               Type:  task           |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.1
           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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 Currently various functions in `Outputable` use `unsafeGlobalDynFlags` to
 get the state of `-dppr-debug`. `unsafeGlobalDynFlags` is rather ugly,
 being a blob of global state spanning both module compilations and GHC API
 sessions. Consequently, we might consider removing it.

 On the other hand, `-dppr-debug` is strictly a debug flag and removing
 `unsafeGlobalDynFlags` would likely require a lot more piping around of
 `DynFlags`. Consequently I suspect our current compromise of using
 `unsafeGlobalDynFlags` is the right solution. Nevertheless, I thought I
 would jot down the task.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14597>
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