[GHC] #9823: --show-iface panics with HEAD

[GHC]

#9823: --show-iface panics with HEAD
-------------------------------------+-------------------------------------
       Reporter:  jstolarek          |                   Owner:
           Type:  bug                |                  Status:  new
       Priority:  normal             |               Milestone:  7.10.1
      Component:  Driver             |                 Version:  7.9
       Keywords:                     |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Moderate (less     |         Type of failure:  GHC
  than a day)                        |  doesn't work at all
     Blocked By:                     |               Test Case:
Related Tickets:                     |                Blocking:
                                     |  Differential Revisions:
-------------------------------------+-------------------------------------
 Let's say I compile an empty module:

 {{{#!hs
 module Foo where
 }}}

 Now, this works:
 {{{
 ghc-stage2 --show-iface Foo.hi
 }}}
 But this panics:
 {{{
 ghc-stage2 Foo.hi --show-iface

 ghc-stage2: panic! (the 'impossible' happened)
   (GHC version 7.9.20141120 for x86_64-unknown-linux):
         ghc-stage2: panic! (the 'impossible' happened)
   (GHC version 7.9.20141120 for x86_64-unknown-linux):
         v_unsafeGlobalDynFlags: not initialised

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 }}}
 Does not happen with 7.8.3. I guess one of recent DynFlags changes must
 have caused this.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9823>
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