Weird parsing in presence of ExtendedLiterals

Summary

I was thinking how various language extensions change the tokenization and parsing of e.g. 123#Int from Haskell2010 to Magic# to the new ExtendedLiterals. Especially if you also turn on RequiredTypeArguments, nowadays the first two can be made to type-check. So I experimented and was surprised to uncover this:

Steps to reproduce

{-# LANGUAGE MagicHash, ExtendedLiterals, RequiredTypeArguments #-}

module Ex where

import GHC.Exts (Int#)

f :: Int# -> forall t -> ()
f _ _ = ()


x = f 0x80#Int
x3 = f 0x80#Int3
--x8 = f 0x80#Int8

With GHC 9.10.1, the above program compiles with no errors. Note there is no type Int3 nor Int3# in scope or anywhere at all, so this should fail even before type-checking. The last line if uncommented does trigger a proper error, saying the expression is of type GHC.Prim.Int8#.

Expected behavior

Report an error for the first line, something like There is no type Int3# in scope. It's not clear if the first line should type-check or not, so it would be nice to have that clarified in the user guide.

Environment

• GHC version used: 9.10.1