fvProv falls into a hole (instead of detecting missing type argument) (regression from -rc1 to -rc2)

This program has an error (T is missing an argument)

data T a ; class C t ; instance C s => C T

which makes 8-rc2 fall into a hole:

/opt/ghc/ghc-8.0.0.20160204/bin/ghc -c Bug.hs
ghc: panic! (the 'impossible' happened)
  (GHC version 8.0.0.20160204 for x86_64-unknown-linux):
	fvProv falls into a hole {ap6}

It is detected by 8-rc1:

/opt/ghc/ghc-8.0.0.20160111/bin/ghc -c Bug.hs

Bug.hs:1:40: error:
    • Illegal instance declaration for ‘C T’
        (All instance types must be of the form (T a1 ... an)
         where a1 ... an are *distinct type variables*,
         and each type variable appears at most once in the instance head.
         Use FlexibleInstances if you want to disable this.)
    • In the instance declaration for ‘C T’

Bug.hs:1:42: error:
    • Expecting one more argument to ‘T’
      Expected a type, but ‘T’ has kind ‘* -> *’
    • In the first argument of ‘C’, namely ‘T’
      In the instance declaration for ‘C T’

Trac metadata

Trac field	Value
Version	8.0.1-rc2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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