Misleading function arity mismatch error with TypeApplications

{-# LANGUAGE TypeApplications #-}

f :: a -> a
f x = x

g :: Int
g = f @Int 42 5

GHCi, version 8.3.20170614: http://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /home/rgscott/.ghci
[1 of 1] Compiling Main             ( Bug.hs, interpreted )

Bug.hs:7:5: error:
    • Couldn't match expected type ‘Integer -> Int’
                  with actual type ‘Int’
    • The function ‘f’ is applied to three arguments,
      but its type ‘Int -> Int’ has only one
      In the expression: f @Int 42 5
      In an equation for ‘g’: g = f @Int 42 5
  |
7 | g = f @Int 42 5
  |     ^^^^^^^^^^^

That error message is quite confusing to read, since it reports that:

• f is applied to three arguments, which //includes// a visible type application
• f only has one argument, which //excludes// the visible type application

We ought to be able to do better. My suggestion would be to report this instead:

    • The expression ‘f @Int’ is applied to two arguments,
      but its type ‘Int -> Int’ has only one
      In the expression: f @Int 42 5
      In an equation for ‘g’: g = f @Int 42 5

Although I'm sure there are other ways the same information could be conveyed (e.g., The function ‘f’ is applied to two value arguments).