[GHC] #14710: GHC 8.4.1-alpha allows the use of kind polymorphism without PolyKinds

[GHC]

#14710: GHC 8.4.1-alpha allows the use of kind polymorphism without PolyKinds
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler (Type    |              Version:  8.4.1-alpha1
  checker)                           |
      Resolution:                    |             Keywords:  PolyKinds
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC accepts       |  Unknown/Multiple
  invalid program                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 You'll need to make a few changes to fix this:

 - `TcHsType.tcLHsKindSig` should really call `checkValidType`. This was an
 oversight from likely long ago.

 - The `tc_infer_hs_type` case that deals with `HsKindSig` should, in turn,
 use `tcLHsKindSig`.

 - `checkValidType` will need to know whether it's checking a kind. If it
 is, and if `-XPolyKinds` isn't on (which is implied by `-XTypeInType`, so
 you don't need a separate `-XTypeInType` check), then complain about
 variables.

 Alternatively, you could conceivably catch this in the renamer.
 `RnTypes.rnHsTyKi` knows when it's renaming a kind (vs. a type). In the
 `HsTyVar` case, you could bleat with `-XNoPolyKinds` and spotting a
 variable whose name is in the type variable namespace (as opposed to a
 tycon, recalling tat `HsTyVar` includes both).

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14710#comment:7>
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