Variable constraints not handled properly in TH

When I compile

{-# LANGUAGE TemplateHaskell, ConstraintKinds #-}

module Scratch where

import Data.Proxy

foo :: $( [t| a b => Proxy a -> b -> b |] )
foo = undefined

I get

    Illegal type constructor or class name: ‛a’
    When splicing a TH type:
      forall a_0 b_1 . a_0 b_1 => Data.Proxy.Proxy a_0 -> b_1 -> b_1
    In the splice: $([t| a b => Proxy a -> b -> b |])

Trac metadata

Trac field	Value
Version	7.9
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Template Haskell
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