[GHC] #15123: mg_arg_tys in MatchGroup should be a PostTc field

[GHC]

#15123: mg_arg_tys in MatchGroup should be a PostTc field
-------------------------------------+-------------------------------------
           Reporter:  mpickering     |             Owner:  (none)
               Type:  task           |            Status:  new
           Priority:  normal         |         Milestone:  8.6.1
          Component:  Compiler       |           Version:  8.2.2
           Keywords:  newcomer       |  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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 It appears that `mg_arg_tys` is only populated after typechecking but the
 type does not indicate this.

 Instead of

 {{{
 mg_arg_tys :: [PostTc p Type]
 }}}

 the type should be

 {{{
 mg_arg_tys :: PostTc p [Type]
 }}}

 All that needs doing is modifying this type in compiler/HsSyn/HsExpr.hs
 and then fixing the resulting compiler errors.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15123>
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