[GHC] #15977: Restructure typechecking modules

[GHC]

#15977: Restructure typechecking modules
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           Reporter:  goldfire       |             Owner:  (none)
               Type:  task           |            Status:  new
           Priority:  normal         |         Milestone:  8.6.3
          Component:  Compiler       |           Version:  8.6.2
           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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 Some of the kind-checking and type-checking modules have become unruly.

 Simon and I propose the new structure:

 - KcTyClsDecls will handle kind-checking and generalization of datatype
 declarations. (That is, `kcTyClGroup` and children, including related
 functions in TcHsType)

 - TcInstBinds will handle `tcInstDecls2` and children

 - TcTyConValidity will handle `checkValidTyCon` and children

 - Fold the rest of TcInstDecls (essentially, `tcInstDecls1`) into what's
 left of TcTyClsDecls. TcInstDecls is removed.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15977>
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