Pattern synonym type signatures

Currently, the only way to specify a type signature for a pattern synonym is by adding type annotations to the right-hand side, like this:

{-# LANGUAGE PatternSynonyms, ScopedTypeVariables #-}

pattern Single x = ([x] :: [Int])

Bespoke syntax for adding type signatures for pattern synonyms would probably be useful.

Link to PatternSynonyms for pattern synonym signatures for specification.