[GHC] #15857: Need for better warnings arising from StarIsType extension

[GHC]

#15857: Need for better warnings arising from StarIsType extension
-------------------------------------+-------------------------------------
           Reporter:  jrp            |             Owner:  (none)
               Type:  feature        |            Status:  new
  request                            |
           Priority:  low            |         Milestone:
          Component:  Compiler       |           Version:  8.6.1
           Keywords:  StarIsType     |  Operating System:  Unknown/Multiple
  NoStarIsType                       |
       Architecture:                 |   Type of failure:  Poor/confusing
  Unknown/Multiple                   |  error message
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 If I redefine `type (*) = (,)` I am given not given a warning that it
 doesn't do what I expect, when building with cabal new-repl or cabal new-
 build, because the `StarIsType` extension is now enabled by default.
 Instead or a warning, I get (correct but confusing) error messages.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15857>
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