[GHC] #14175: Panic repSplitTyConApp_maybe

[GHC]

#14175: Panic repSplitTyConApp_maybe
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        Reporter:  dfeuer            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.2.2
       Component:  Compiler (Type    |              Version:  8.2.1
  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:  #13910            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"8bf865d3db69c6f4a09f3e5e3880c087c0a7c7f0/ghc"
 8bf865d3/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="8bf865d3db69c6f4a09f3e5e3880c087c0a7c7f0"
 Tidying could cause ill-kinded types

 I found (Trac #14175) that the tidying we do when reporting
 type error messages could cause a well-kinded type to become
 ill-kinded. Reason: we initialised the tidy-env with a
 completely un-zonked TidyEnv accumulated in the TcLclEnv
 as we come across lexical type-varialbe bindings.

 Solution: zonk them.

 But I ended up refactoring a bit:

 * Get rid of tcl_tidy :: TidyEnv altogether

 * Instead use tcl_bndrs :: TcBinderStack
   This used to contain only Ids, but now I've added those
   lexically scoped TyVars too.

 * Change names:
      TcIdBinderStack -> TcBinderStack
      TcIdBinder      -> TcBinder
      extendTcIdBndrs -> extendTcBinderStack

 * Now tcInitTidyEnv can grab those TyVars from the
   tcl_bndrs, zonk, and tidy them.

 The only annoyance is that I had to add TcEnv.hs-boot, to
 break the recursion between the zonking code and the
 TrRnMonad functions like addErrTc that call tcInitTidyEnv.
 Tiresome, but in fact that file existed already.
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14175#comment:7>
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