Agressive name shadowing warning

Using current master (1b1a92bd), the following code

module Repro where

foo x = res
  where
    blah = case x of
        [] -> []
        xs -> hh
          where
            hh = xs
    hh = blah -- Shadowing the `hh` introduced on the line above
    res = hh

complains that hh is shadowed as per the comments.