Unreadable unicode in type-level literals

[dpwiz]

Your environment

• ghcup-compiled LSP from a recent-ish master
• VS Code extension v2.2.1
• GHC 9.2.4
• Ubuntu

Steps to reproduce

type family (label :: Symbol) ::: a where
  label ::: a = a

type Example = "привет" ::: Int

x :: Example
x = 4

Hover over 4 to see its type.

Expected behaviour

The label should be preserved since it's a valid Haskell symbol: _ :: "привет" ::: Int.

Actual behaviour

The label escaped into _ :: "\1087\1088\1080\1074\1077\1090" ::: Int.

[michaelpj]

Our handling of unicode is pretty broken in general, but we should at least render it properly in hovers. I have a suspicion that this may ultimately be https://gitlab.haskell.org/ghc/ghc/-/issues/20027, however. So the solution may mean replacing some deep usage of Show with something better behaved... probably from text.

[dpwiz]

20027 was superceded then withdrawn. I'd expect no improvement from the Show side.

[kokobd]

I located the line producing the message:

haskell-language-server/ghcide/src/Development/IDE/Spans/AtPoint.hs

Line 254 in 5b229b6

HieFresh -> printOutputable t

printOutputable indirectly calls this function in ghc: https://hackage.haskell.org/package/ghc-9.2.4/docs/src/GHC.Iface.Type.html#pprIfaceTyLit

pprIfaceTyLit :: IfaceTyLit -> SDoc
pprIfaceTyLit (IfaceNumTyLit n) = integer n
pprIfaceTyLit (IfaceStrTyLit n) = text (show n)
pprIfaceTyLit (IfaceCharTyLit c) = text (show c)

You see, it calls show on a FastString. Show for FastString is defined by converting to String then call show on String.