[GHC] #13601: GHC errors but hangs

[GHC]

#13601: GHC errors but hangs
-------------------------------------+-------------------------------------
        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:  TypeInType,
                                     |  LevityPolymorphism
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by simonpj):

 I know roughly what is happening here.

 * When checking kinds we call `solveEqualities` which immediately reports
 type errors

 * The offending kind-equality constraint in this case has a `TypeEqOrigin`
 whose `uo_thing` is built by `checkExpectedKind`.

 * That `uo_thing` is printed as part of the error message.  Alas it
 contains a type (not a kind); and that type involves some knot-tied
 `TyCons`.  Result: black hole.

 The exact details are still hazy to me.  The entire `uo_thing` stuff seems
 pretty grim.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13601#comment:3>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler