[GHC] #11755: Seed unsafeGlobalDynFlags with enough information to use ppr

[GHC]

#11755: Seed unsafeGlobalDynFlags with enough information to use ppr
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        Reporter:  bgamari           |                Owner:  bgamari
            Type:  task              |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D2036
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"4e98b4ff98e127aa9ef4fa1e85bdf0efa41f0902/ghc" 4e98b4f/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="4e98b4ff98e127aa9ef4fa1e85bdf0efa41f0902"
 DynFlags: Initialize unsafeGlobalDynFlags enough to be useful

 Previously unsafeGlobalDynFlags would bottom if used prior to
 initialization. This meant that any attempt to use the pretty-printer
 early in the initialization process of the compiler would fail. This is
 quite inconvenient.

 Here we initialize unsafeGlobalDynFlags with defaultDynFlags, bottoming
 only if settings is accessed.

 See #11755.

 Test Plan: Validate

 Reviewers: austin

 Reviewed By: austin

 Subscribers: thomie, gridaphobe

 Differential Revision: https://phabricator.haskell.org/D2036

 GHC Trac Issues: #11755
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11755#comment:2>
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