GHC shows core with error

The following code intentionally does not compile:

{-# LANGUAGE DataKinds, KindSignatures, PolyKinds #-}

data Proxy (p :: k) = Proxy
data Tagged (t :: k) s = Tagged s

proxy :: Tagged t s -> Proxy t -> s
proxy = undefined

bar :: Tagged (gad :: *) Int
bar = undefined

foo :: Int
foo = proxy bar (Proxy::Proxy 'True)

but it produces the following output with GHC and GHCi:

[1 of 1] Compiling Main             ( Bug.hs, interpreted )
RAE1
  [W] cobox_aLM :: t0_aK4[tau:1] ~ 'True (CNonCanonical)
  t0_aK4[tau:1]
  'True
  False

Bug.hs:13:18:
    Couldn't match kind ‘Bool’ with ‘*’
    Expected type: Proxy t0
      Actual type: Proxy 'True
    In the second argument of ‘proxy’, namely ‘(Proxy :: Proxy True)’
    In the expression: proxy bar (Proxy :: Proxy True)
    In an equation for ‘foo’: foo = proxy bar (Proxy :: Proxy True)
Failed, modules loaded: none.

This ticket is about the first block printed out. It seems to be a random section of core, and is completely useless to debugging the problem.

Trac metadata

Trac field	Value
Version	7.10.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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