[GHC] #11648: assertPprPanic, called at compiler/types/TyCoRep.hs:1932

[GHC]

#11648: assertPprPanic, called at compiler/types/TyCoRep.hs:1932
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        Reporter:  thomie            |                Owner:  goldfire
            Type:  bug               |               Status:  merge
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
                                     |  polykinds/T11648{,b}
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 A few comments for posterity on the commit above:

 A lot of the changes are due to moving decisions out from kcHsTyVarBndrs,
 and thus the need to store information in the AST:
 - It turned out to be more convenient to decide if a data decl has a CUSK
 in the renamed than on the fly. (It could be done on the fly, but it would
 have been a bit hairy and duplicated code in the renamer.) See the new bit
 in the manual for a description of what's going on here.
 - There also needed to be a decision about whether to use `Anon` or
 `Named` when building the `TcTyBinder`s of a tycon's kind. Previous to
 this patch, this was done in `kcHsTyVarBndrs`, but -- as Simon pointed out
 to me -- this was bogus (it looked at the free variables of a not-yet-
 solved-or-zonked type). So it's now done via a simple syntactic check in
 the renamer. But then the result of the check must be put in the AST,
 causing knock-on changes. See `Note [Dependent LHsQTyVars]` in !TcHsType
 and also a new bit in the manual.
 - One of this issues brought up in the ticket is the handling of CUSKs for
 associated type families. An associated type/data family's CUSKness must
 be inherited from the enclosing class. Previously, all associated families
 had CUSKs, but this was wrong. So the CUSK check is a bit more intricate
 to allow for this relationship.
 - Along the way, I made `(->)`, when used in a kind, have type `* -> * ->
 *`, instead of being polymorphic in `RuntimeRep`s. We don't have type-
 level representation polymorphism.
 - Also incidental to this patch, I made kind variables have kind `*` when
 `-XTypeInType` is not in effect. Not doing this earlier was an oversight.
 The check isn't perfect, as it's sometimes hard to tell what's a kind
 variable and what isn't; currently, only variables used in kinds in tycon
 `LHsQTyVars` are affected, and these are surely kind variables. (This is
 `mk_kv_kinds` in `kcHsTyVarBndrs`.)
 - There is a new function `anonymiseTyBinders`. This was necessary in an
 earlier version of this patch but is now redundant (and harmless). I will
 remove.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11648#comment:22>
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