[GHC] #14880: GHC panic: updateRole

[GHC]

#14880: GHC panic: updateRole
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        Reporter:  RyanGlScott       |                Owner:  goldfire
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.8.1
       Component:  Compiler (Type    |              Version:  8.2.2
  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:  #15076            |  Differential Rev(s):  Phab:D4769
       Wiki Page:                    |
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Comment (by simonpj):

 > But Simon's approach applied to your patch doesn't

 Gah! This zombie keeps rising from the dead.

 I suggest

 '''Step 1''': improve `tyCoVarsOfType`.

 * Apply my patch to HEAD, with the fix in `ty_co_vars_of_co_var`.
 * Check that it's a win -- generally perf should improve slightly
 * Commit

 Now move on to this ticket

 '''Step 2:''' deal with `Note [Closing over free variable kinds]` (this
 note is in Richard's original patch).

 This is a change that fixes an outright bug, albeit one that has not been
 reported.  I think it is nothing to do with the original `updateRole`
 problem.

 * Invite Richard to implement `Note [Closing over free variable kinds]` in
 `TyCoRep`, based on his patch.  This will take him (or me) 20 mins.  I
 think the only changes are in `TyCoRep`.
 * Do perf tests.

 '''Step 3'''. Back to this ticket and `updateRole`:

 * Apply the rest of Richard's patch, ''except'' the stuff in `TyCoRep`
 * Test

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14880#comment:108>
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