assertPprPanic, called at compiler/types/TyCoRep.hs:1932

As mentioned in https://mail.haskell.org/pipermail/ghc-devs/2016-February/011455.html, the following tests currently hit an assert when the compiler is built with -DDEBUG:

   patsyn/should_compile  MoreEx [exit code non-0] (normal)
   patsyn/should_compile  T11224b [exit code non-0] (normal)
   polykinds              MonoidsTF [exit code non-0] (normal)
   polykinds              T11480b [exit code non-0] (normal)
   polykinds              T11523 [exit code non-0] (normal)

Compile failed (status 256) errors were:
ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 8.1.20160218 for x86_64-unknown-linux):
ASSERT failed!
  CallStack (from HasCallStack):
  assertPprPanic, called at compiler/types/TyCoRep.hs:1932:56 in ghc:TyCoRep
  checkValidSubst, called at compiler/types/TyCoRep.hs:1991:17 in
ghc:TyCoRep
  substTys, called at compiler/types/TyCoRep.hs:2012:14 in ghc:TyCoRep
  substTheta, called at compiler/typecheck/TcPatSyn.hs:255:20 in
ghc:TcPatSyn
  in_scope InScope {d_ap0 c_apv}
  tenv [ap1 :-> c_apv[tau:5]]
  tenvFVs [aps :-> t_aps[tau:1], apv :-> c_apv[tau:5]]
  cenv []
  cenvFVs []
  tys []
  cos []

D1951 contained a stopgap patch, but since it wasn't accepted, I'll just mark the tests as expect_broken for this ticket, so that other developers aren't bothered by this issue.

The offending commit is b5292557.

Trac metadata

Trac field	Value
Version	8.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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