[GHC] #16347: GHC HEAD regression: piResultTys1

[GHC]

#16347: GHC HEAD regression: piResultTys1
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:
       Component:  Compiler (Type    |              Version:  8.7
  checker)                           |
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by goldfire):

 In conversation, Simon and I uncovered an unstated invariant: the
 `tyVarKind` of occurrences of a bound tyvar must share the `tyVarKind` of
 the binding site. In this example, that is not the case, because the kind
 of the tyvar contains a metavariable; it is zonked at an occurrence but
 not at the binding site.

 The fix is easy: do an extra zonk in `kcLHsQTyVars_NonCusk`, but fixing
 #16344 will also make this problem melt away.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16347#comment:4>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler