Bad error message if we use TypeApplications with an identifier that doesn't exist

{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE DataKinds #-}
module BadError where

foo :: Int
foo = doesNotExist @123

{-
[1 of 1] Compiling BadError         ( BadError.hs, BadError.o )

BadError.hs:6:7: error:
    • Cannot apply expression of type ‘t1’
      to a visible type argument ‘123’
    • In the expression: doesNotExist @123
      In an equation for ‘foo’: foo = doesNotExist @123
  |
6 | foo = doesNotExist @123
-}

What I would expect is for it to say that doesNotExist is not bound as one might reasonably expect. This is very, very confusing and easy to hit in real life. If you are exposing a function f, using it somewhere with f @123 but then later decide to remove or rename f, the error message doesn't suggest at all that f has disappeared and leaves the user scratching their head.

Trac metadata

Trac field	Value
Version	8.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed weight to 5

added Tbug Trac import labels

closed

Thanks for the bug report. This is "fixed" in GHC 8.8 in the sense that it will at least report that doesNotExist is not in scope:

[1 of 1] Compiling BadError         ( Bug.hs, interpreted )

Bug.hs:6:7: error: Variable not in scope: doesNotExist
  |
6 | foo = doesNotExist @123
  |       ^^^^^^^^^^^^

Bug.hs:6:7: error:
    • Cannot apply expression of type ‘t1’
      to a visible type argument ‘123’
    • In the expression: doesNotExist @123
      In an equation for ‘foo’: foo = doesNotExist @123
  |
6 | foo = doesNotExist @123
  |       ^^^^^^^^^^^^^^^^^

Of course, there's still the confusing "Cannot apply expression" part. That has previously been reported as #13834 (closed), so to avoid ticket duplication, I'll close this ticket in favor of that one.

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedDuplicate
Related	- → #13834 (closed)

added Pnormal label