When printing type signatures of types, GHC always prints ASCII double colon and never prints Unicode proportion symbol.

Summary

I have the setting -fprint-unicode-syntax switched on. However, GHC still prints type signatures of types with the ASCII double semicolon. It would print Unicode stars ★ and Unicode arrows → on the same very line, so this is specific to the double semicolon.

Steps to reproduce

Start ghci and type :set -fprint-unicode-syntax then :info IO. You shall see:

λ :info IO
type IO :: ★ → ★
…

(ellipsis mine)

This is wrong!

Expected behavior

λ :info IO
type IO ∷ ★ → ★
…

(ellipsis mine)

Environment

GHC version used: 9.2.8, 9.6.2.

Optional:

Operating System: Linux
System Architecture: x86_64

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