[GHC] #9821: DeriveAnyClass support for higher-kinded classes + some more comments

[GHC]

#9821: DeriveAnyClass support for higher-kinded classes + some more comments
-------------------------------------+-------------------------------------
       Reporter:  dreixel            |                   Owner:  dreixel
           Type:  bug                |                  Status:  new
       Priority:  normal             |               Milestone:  7.10.1
      Component:  Compiler           |                 Version:  7.9
       Keywords:                     |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Unknown            |         Type of failure:
     Blocked By:                     |  None/Unknown
Related Tickets:  #5462              |               Test Case:
                                     |                Blocking:
                                     |  Differential Revisions:
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 #5462 was merged before a few final fixes were done. This ticket serves to
 record that. Left to address are:

 https://phabricator.haskell.org/D476?id=1443#inline-3652

 https://phabricator.haskell.org/D476?id=1443#inline-3648

 https://phabricator.haskell.org/D476?id=1443#inline-3646

 Also, `DeriveAnyClass` currently panics at higher-kinded classes (like
 `((* -> *) -> *) -> Constraint`).

 I'll fix this.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9821>
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